QUANTITATIVE CHEMICAL ANALYSIS, determination of the quantitative content of the components of the analyte; one of the main types of chemical analysis. Based on the nature of the particles being determined, there are isotopic analysis, elemental analysis, molecular analysis, phase analysis, structural group (functional) analysis, and other types of analysis. The content of the determined component (analyte) is characterized by the following quantities: amount of substance, mass, mass fraction, mole fraction, concentration, molar or mass ratios of components. The main characteristic is the amount of substance (v, mol). More often, the mass fraction of the analyte (ω, %) is determined proportional to the amount of substance.
Quantitative chemical analysis is a type of indirect measurement (see the article Metrology of chemical analysis). Quantitative chemical analysis is fundamentally different from conventional measurements in the absence of a standard unit of quantity of a substance (mole). In addition, non-measuring stages (sampling, sample preparation, identification) play an important role in quantitative chemical analysis, so the error of the analysis result is higher than the total error of the initial measurements (mass, volume, etc.). Achieving the uniformity of measurements in quantitative chemical analysis is difficult and is implemented in specific ways - using standard samples of the composition, as well as by comparing the results obtained in different laboratories.
For quantitative chemical analysis, chemical, physicochemical, physical, as well as biochemical and biological methods are used. Their relative importance varied: in the 18th and 19th centuries gravimetry and titrimetry were the main ones, in the middle of the 20th century - spectral analysis, photometric analysis and electrochemical methods of analysis. At the turn of the 20th and 21st centuries, chromatography, various types of spectroscopy and mass spectrometry play a leading role. The general theoretical and metrological foundations of quantitative chemical analysis are rapidly developing, chemometric methods have begun to be applied, computerization and automation of analysis continues, and attention to economic aspects is growing.
The analysis technique specifies the chosen method and regulates the sequence, methods and conditions for performing all operations when analyzing objects of a known type into given components. The analyte must be previously detected and identified by qualitative chemical analysis methods. It is desirable to know in advance the approximate content of the analyte, as well as substances that may interfere with the analysis. The technique is characterized by the lower limit of the determined contents (LLI), that is, the minimum content of the analyte, at which the relative error of the analysis remains below the specified limit with a probability of 0.95. Usually, NGOS is an order of magnitude higher than the detection limit - the minimum content of the analyte required for its detection by this method with a given reliability. There are also upper limits of determined contents.
Most methods of quantitative chemical analysis include the following stages: sampling, sample preparation (grinding, decomposition, dissolution, separation or masking of interfering substances, transformation of the analyte into a new form), measurement of the analytical signal, calculation of the analyte content. Some methods (for example, using chemical sensors or chemical analysis test methods) do not require sampling or sample preparation. To calculate the content of the analyte, the analytical signal (I) is measured - a physical quantity that is functionally related to the content of the analyte in the sample (in semi-quantitative methods, the signal is evaluated visually). The nature of the analytical signal is different: in gravimetry it is the mass of the reaction product, in titrimetry it is the volume of the titrant, in potentiometry it is the electrode potential, in atomic emission spectral analysis it is the radiation intensity at a certain wavelength. The measurement of an analytical signal is often combined with a chemical reaction (physico-chemical methods of analysis) or with separation of components (hybrid methods of analysis).
The calculation of the analyte content (c) usually requires knowledge of the calibration characteristic - the dependence of the form I = f(c). In relative methods of quantitative chemical analysis (most methods), this dependence is set using reference samples for which the analyte content is precisely known, and analytical signals are measured by the same means and under the same conditions as in subsequent analyses. In absolute methods (for example, gravimetry, titrimetry, coulometry), reference samples are usually not used, and calibration characteristics are obtained based on general chemical information (reaction stoichiometry, the law of equivalents, Faraday's law, etc.).
The results of quantitative chemical analysis are subjected to mathematical processing, which includes the rejection of gross errors, the assessment of the compatibility of the results of repeated analyzes, their averaging to reduce the influence of random errors, the exclusion of systematic errors, the calculation of a confidence interval in which, with a probability P (usually P = 0.95), get the actual content of the analyte. When processing the results of quantitative chemical analysis, comparing them with each other or with technical standards, the statistical distribution of the results of repeated analyzes is taken into account.
When choosing and evaluating methods of quantitative chemical analysis, high accuracy is important (random and systematic errors should be as small as possible), high sensitivity (characterized by the slope of the calibration characteristic dl / de), absence or constancy of the background (signal arising in the absence of an analyte), high selectivity (the signal should not depend on the content of other components of the sample), rapidity (the duration of the analysis should be as short as possible). Other characteristics of the technique are also important (sample weight, cost and complexity of equipment, labor intensity of analysis, the possibility of automating analysis, continuous signal recording, and simultaneous determination of a number of analytes). Continuous automated quantitative chemical analysis is essential for effective process control, environmental monitoring, and more.
Lit .: Fundamentals of analytical chemistry: In 2 books. / Under the editorship of Yu. A. Zolotov. M., 2004; Zolotov Yu. A., Vershinin VI History and methodology of analytical chemistry. 2nd ed. M., 2008.
R 50.2.008-2001
State support system
unity of measurements
TECHNIQUES FOR QUANTITATIVE
CHEMICAL ANALYSIS
GOSSTANDART OF RUSSIA
Moscow
Foreword
1 DEVELOPED by the State Unitary Enterprise All-Russian Research Institute of Metrology. DI. Mendeleev State Standard of Russia
INTRODUCED by the Department of Metrology of the State Standard of Russia
2 ADOPTED AND INTRODUCED BY Decree of the State Standard of Russia dated June 20, 2001 No. 244-st
3 INTRODUCED FOR THE FIRST TIME
R 50.2.008-2001
State system for ensuring the uniformity of measurements
QUANTITATIVE CHEMICAL ANALYSIS TECHNIQUES
Introduction date 2002-01-01
1 area of use
These recommendations are intended for state scientific metrological centers conducting metrological examination of documents for methods of quantitative chemical analysis (hereinafter referred to as metrological examination of the MKCA) in accordance with GOST R 8.563.
2 Normative references
GOST 8.221-76 State system for ensuring the uniformity of measurements. Moisture and hygrometry. Terms and Definitions
a) a document or a draft document regulating the ICCA;
b) terms of reference for the development of the ICA or another document containing the initial data for development (except when the relevant data are contained in state, interstate or international standards applicable to the analyzed object);
c) a copy of the certificate of metrological certification of the ICCA (if it was carried out). At the same time, the Applicant may submit additional materials: the program and results (in the form of reports, protocols) of the experimental or computational evaluation of the metrological characteristics of the MKCA, regulatory documents (including departmental ones) regulating the control of the accuracy of measurement results, etc. In addition, additional materials are submitted Applicant at the request of the SSMC conducting the examination (see).
If the Applicant considers it necessary to formulate questions for examination, they must be set out in writing (for example, in a cover letter to the SSMC).
5 Contents of the metrological examination of the ICCA
5.1 In the general case, during the metrological examination, the MKCA is subjected to critical analysis (evaluate):
The correctness of the names of the measured quantities and the designations of their units;
Choice of measuring instruments (including standard samples);
Compliance of the metrological characteristics of the MKCA with the specified requirements;
Procedures for monitoring the error of measurement results;
Completeness of statement of requirements, rules and operations;
Correctness of metrological terms.
5.2 At the request of the Applicant or in connection with the peculiarities of the purpose of the ICCA, other aspects can be considered during the metrological examination, for example: the metrological level of this technique in relation to other methods of a similar purpose, the prospects for standardization of the ICCA, the rationality of the choice of the method of analysis.
6 The procedure for the metrological examination of the ICCA
6.1 The metrological examination of the MKCA is carried out by an expert or a group of experts authorized by the head (deputy head) of the SSMC.
An expert can be an employee of the SSMC who has worked in it for at least three years, has experience in attestation (development) of at least five IACs, and is familiar with domestic and international regulatory documents related to ensuring the uniformity of measurements. It is preferable that the expert (leader of the group of experts) has a basic higher education in the field of chemistry and is a certified expert of the Accreditation System for Analytical Laboratories (Centers). The expert should be aware of the general principles and methods for estimating the measurement error -, features of CCA as a measuring procedure, specific methods and techniques for ensuring the reliability of CCA results -, the role and place of CCA in monitoring product quality and the state of environmental objects -. The expert should systematically improve his qualifications, in particular, get acquainted with the relevant publications in specialized scientific and technical periodicals.
Experts are responsible for the correct, objective and timely performance of work, as well as for non-dissemination of confidential information. The head of the group of experts formulates tasks for the members of the group, summarizes their assessments and opinions.
6.2 The metrological examination of the MKCA includes the following stages:
Registration of documents submitted for examination;
Preliminary analysis of documents;
Request for additional documents (if necessary), their registration;
Assessing the compliance of the ICCA with metrological requirements;
Drawing up an expert opinion, its approval and transfer to the Applicant.
6.3 Documents received for metrological examination are registered in a journal, the recommended form of which is given in. It is allowed to combine the registration of documents at the ICCA with the registration of other types of documents subject to metrological examination, for example, draft standards.
7.2.5 When presenting the ICCA, which regulate the measurement of several quantities characterizing the chemical composition, their general name is sometimes used: “contenti ]. When examining such ICCA, it is necessary to make sure that the use of a generic name does not lead to a reduction or distortion of measurement information, does not create prerequisites for different interpretations of the ICCA text. A generalizing name should not be used when describing specific measurement tasks, when indicating metrological characteristics, as well as in explanations of calculation formulas and when reporting measurement results.
7.2.6 Units of measured values must comply with GOST 8.417, taking into account the governing document.
7.2.7 Examples of typical errors:
a) “The amount of zinc in 10 cm 3 of a solution is 15 mmol” instead of the correct “Amount of zinc substance in 10 cm 3 of a solution is 15 mmol”;
b) “Dissolved oxygen 60 µmol / dm 3” instead of the correct “Molar concentration of dissolved oxygen 60 µmol, dm 3”;
d) “Number of cadmium ions in the calibration solution 2.00 μg/5 cm 3 ” instead of the correct “Mass of cadmium in 5 cm 3 of the calibration solution 2.00 μg”;
e) "Dry residue in water 5 mg / 100 g" instead of the correct "Mass fraction of dry residue in water 0.05%".
7.3 Evaluation of the choice of measuring instruments
a) conformity of the purposes of application of the selected measuring instrument (including the standard sample) with the purpose fixed in the description of the type or in the technical documents for the measuring instruments;
b) the possibility of using a measuring instrument under specified conditions;
c) achievability of the required accuracy of measurement results when using a measuring instrument with metrological characteristics established for this type;
d) the rationality of the choice of measuring instruments;
e) compliance with the requirements for measuring instruments used in the field of distribution of state metrological control and supervision.
7.3.2 Information about the purpose and main characteristics of measuring instruments of approved types can be borrowed from descriptions of types, from publications in the journals "Izmeritelnaya Tekhnika", "Legislative and Applied Metrology", as well as from databases formed by VNIIMS (for measuring instruments) and UNIIM (for state standard samples).
7.3.3 The achievability of the required accuracy is assessed by calculating the limits of the corresponding instrumental component of the error of the measurement results and comparing the found value with the limits (boundaries) of the error specified in the document for the ICCA. This procedure is sufficient in cases where the instrumental component of the error prevails over the methodological one.
Examples of detected errors:
a) To measure the height of the chromatographic peak, a ruler with a division value of 1 mm is used; tolerance limits ± 0.5 mm. The height of the peak of the determined component, corresponding to the lower limit of the mass concentration of the component in the analyzed object, is» 4 mm. The limits of the relative error of measuring the peak height in this case will be ± 12%, which clearly does not correspond to the assigned error characteristic of the measurement result of the mass concentration of the component ± 10%, indicated in the document for the MKCA.
b) The method for measuring the mass concentration of a component in the emissions of an industrial enterprise involves taking a gas sample using an aspirator (at a constant value of its volumetric flow rate of 4 dm 3 /min) into an absorption solution and subsequent analysis of the solution by the photocolorimetric method. The norm for the limits of the relative error in measuring the mass concentration of a component when monitoring sources of atmospheric pollution is ± 25%. The limits of the relative error in the analysis of the absorbing solution by the photocolorimetric method are usually 10% - 20%. To measure the volumetric flow rate of the gas flow, a rotameter is used with an upper measurement limit of 20 dm 3 /min and the limits of the permissible basic reduced error of ± 5%. The limits of the relative error of volumetric flow measurements (with the introduction of corrections) will be ± 25%. Comparison of the values of the components of the error with the norm indicates the impossibility of achieving the required accuracy when using the selected type of flowmeter.
7.3.4 When evaluating the rationality of the choice of measuring instruments, recommendations , , , as well as GOST R 1.11 can be used.
7.3.5 If the MKCA is intended for use in the field of distribution of state metrological control and supervision, then the expert must make sure that the types of measuring instruments used are registered in the State Register of Approved Types of Measuring Instruments, standard samples - in the State Register of Approved Types of Standard Samples.
7.3.6 It should be borne in mind that the sampling and dosing devices used in the IAC may have either the status of measuring instruments or the status of auxiliary equipment. In the latter case, evaluation is not carried out.
7.3.7 Along with substances and materials that have the status of measuring instruments (standard samples of the composition and properties of substances and materials according to , VNIIM reference materials according to , certified mixtures according to ), pure substances and reagents produced according to standards and specifications can perform the functions of measures in the ICCA. manufacturer's conditions (substances of known composition according to), as well as pure substances, solutions, mixtures obtained according to the procedure regulated in the document for the ICCA.
7.4 Evaluation of the conformity of the metrological characteristics of the MEXA to the specified requirements
a) terms of reference for the development of the ICCA or other documents, the requirements of which apply to this ICCA. (Such documents can be standards, specifications, guidelines, test programs, etc.);
b) GOST R 8.563 - in terms of indicating the measurement range and the form of presentation of the error characteristics.
The task of the expert is also to identify unreliable attributed characteristics of the measurement error or erroneous conclusions about the compliance of the measurement error with the established standards.
7.4.2 The measurement ranges indicated in the document for the MKCA (ranges of values of the measured quantity) and the assigned error characteristics are compared with the requirements given in the documents on, listing a).
Examples : The metrological characteristics of the MKHA of natural and waste waters are compared with the requirements of GOST 27384 and GOST 8.556, the metrological characteristics of the MKHA of atmospheric air are compared with the requirements of GOST 17.2.4.02.
7.4.3 If the requirements for error are not explicitly established, then the limits (limits) of the error specified in the document for the MKCA are compared with a tolerance for a controlled value.
Example . The technical specifications for the chemical product indicate that the mass fraction of the impurity component "B" (WV) should not exceed 0.50%. During the control, it is necessary to reliably distinguish a product of good quality fromWV= 0.50% and product withWV= 0.51%. To do this, it is necessary to obtain measurement results, the error of which does not exceed 0.003% (with appropriate economic justifications - 0.005%).
Useful guidelines for making such comparisons are provided in the recommendations , , ; for chemical analysis, the methodology is described in .
7.4.4 Sometimes the developers of the MKCA do not limit the measurement range from above, referring to the possibility of varying the mass of the sample taken for analysis, its dilution, etc. This practice does not meet the requirements of GOST R 8.563.
Other examples of inconsistencies:
Indication of "limit of detection" instead of the lower limit of the measurement range;
Representation of the characteristics of the measurement error in a form that does not allow specifying its value for each of the values of the measured quantity in the measurement range;
Indication of the characteristics of only the random component of the error;
Indication of the error control standard (without specifying the error characteristic).
7.4.5 If the expert doubts the reliability of the attributed characteristics of the measurement error or the correctness of the conclusions about the compliance of the measurement error with the established standards, then he must approximately calculate the error limits. Sources of doubt can be the personal experience and intuition of an expert, significant differences in the error characteristics from those established for similar ICCA, a clearly simplified data processing algorithm, inconsistency in the characteristics and standards for error control, etc.
In most cases, it is advisable to carry out such a calculation for the smallest (largest) value of the measured quantity. The general calculation methodology is described in , , calculation algorithms are given in , -, in relation to chemical analysis - in the recommendations , . In addition, experts may refer to the EURAHIM document. The expanded uncertainty calculated in accordance with this document (at coverage factors of 2 and 3) is almost equal to the margin of error at a confidence level of 0.95 and 0.99.
When performing calculations, the expert should rely on the experimental data provided by the Applicant, information on the metrological characteristics of measuring instruments, standards for controlling error components (if they are given in the document for the ICCA).
a) the term "error" is used instead of "margin of error" or "margin of error";
b) the term “error characteristic” (or “accuracy indicator”) is used without specifying which characteristic is meant: “error margins”, “error limits” or “standard deviation of error”;
c) the term "margin of error" is used with an indication of a probability other than one;
d) the term "margin of error" is used without indicating the confidence level;
e) the limits of the relative error are indicated with an excessive number of significant figures (for example, ± 19.8% instead of ± 20%);
f) the limit of the measurement range is indicated with an excessive number of significant figures (for example, 100.0 mg/dm 3 instead of 100 mg/dm 3);
g) the limits of the relative measurement error of the mass fraction of the main component in the technical product are indicated without taking into account the limitations imposed by the physical model (± 2.0% for the upper limit of the measurement range of 99.5%);
i) the limits of the relative error of the measurement result of the volume fraction of the impurity component in the technical product are ± 100%;
j) the values of the characteristics of the random component of the error are indicated without explanation of the conditions to which they correspond (for example, conditions of convergence, intra- or inter-laboratory reproducibility);
l) the error characteristic is established only for the simplest model mixture (i.e. without taking into account real accompanying components) or for an unreasonably narrowed range of values of external influencing factors;
l) the error characteristic is established without taking into account the stages of sampling and sample preparation, although these stages are included in the ICA.
7.5 Evaluation of measurement uncertainty control procedures
7.5.1 The expert assesses:
Availability of operational control procedures in the ICCA;
The correct choice of means of control;
Interconnection of control standards and measurement error characteristics.
7.5.2 It should be borne in mind that the control procedure may cover all stages of the ICCA at once (“integrated control”) or only some of them. Methods for comprehensive control of measurement errors (analyses), as well as their convergence and reproducibility, are described in the recommendation. The control of individual stages is carried out in cases where complex control cannot technically be implemented or is irrational. Such control can also be carried out in addition to the complex one; in this case, most often they control the degree of separation or extraction of components, the error in constructing the calibration characteristic and its stability. In all cases when the value of the measured value (including intermediate) is calculated by averaging the results obtained during repeated measurements (determinations), it is advisable to control their convergence.
7.5.3 The document for the MKCA may not describe the error control procedures, but it must contain an indication of the control in accordance with any regulatory document.
Example . When analyzing drinking water, error control can be carried out according to GOST R 51232; when analyzing gold - according to GOST 27973.0; when analyzing mineral raw materials - according to the industry standard; when analyzing natural water in the network laboratories of Roshydromet - according to the guidance document.
7.5.4 When evaluating the correctness of the choice of control means, the expert must pay attention to the ratio of the boundary (limit) of the error of the measurement result according to the MKCA to the boundary (limit) of the error of the control. To ensure the reliability of control, this ratio, as a rule, should be at least 3 (if there is an appropriate justification, at least 2).
If a mixture (solution) is used as a means of control, the method of preparation of which is described in the appendix to the ICA, then the expert must approximately calculate the margins of error with which the content of the analyte in the mixture (solution) is established. In this case, recommendations can be applied.
If a standard sample is used as a means of control, then its category should correspond to the scope of the ICAC.
7.5.5 When evaluating the interdependence of operational control standards and measurement error characteristics, it is advisable to be guided by the recommendation for integrated control, recommendations , - for control of the construction error and stability of the calibration characteristic. The expert should pay attention to the clarity of the formulation of the conditions for the control of intralaboratory reproducibility, since the control standard depends on which of the factors (time, operator, equipment, calibration) vary from analysis to analysis. This dependence also takes place when controlling the error by the method of additions; sample dilution method; a method that combines additive and dilution. If the analysis of the sample without additive and with the additive is carried out under conditions of constancy of the above factors, then the error control standard calculated by the method will be significantly overestimated.
7.5.6 Examples of typical errors:
a) the terms "control of the convergence of the results of determinations", "standard for the control of the convergence of the results of determinations" are used without indicating which parameter is controlled: "the range of the results of the determinations", "deviation of the result of the determination from the arithmetic mean ...", the standard deviation of the results definitions”, “standard deviation of the arithmetic mean...”, etc.;
b) the allowable discrepancy between the two results of the analysis is given without specifying the conditions for obtaining them and the confidence level;
d) the standard for "the range of two results of parallel determinations, referred to the arithmetic mean ( R = 0.95)”, equal to 30%, does not agree with the limits of the relative error of the analysis result ± 10%, R= 0.95 (analysis includes two determinations).
7.6 Evaluation of the completeness of the statement of requirements, rules and operations
7.6.1 The examiner should review the sections of the ICCA document and its appendices in sequence. At the same time, it is advisable to ask the questions: “Is there enough information to conduct an analysis with the required accuracy?”, “Are there any provisions in this section that are not consistent with the requirements of GOST R 8.563, other state standards, or with other provisions of the document for the ICCA?”, “Not does this wording allow for various interpretations that can cause uncontrollable error?
7.6.2 The expert should pay special attention to those requirements (rules, operations) that most affect the quality of the data received. In this case, it is necessary to be guided by the information available in the literature on the limitations and sources of error characteristic of the methods of sampling and analysis being implemented, as well as the estimates obtained when calculating the error limits of the measurement results (see ).
7.6.3 The shortcomings most often found in the documents for the ICCA:
Limitations due to interfering sample components are not specified;
The requirements for the content of the main component in the pure substance used for the preparation of calibration mixtures have not been formulated;
The shelf life of calibration mixtures has not been established;
There are no calibration quality criteria;
The criteria for identification of components, separation criteria (when analyzing multicomponent samples by chromatography, mass spectrometry, spectrophotometry, etc.) are not given;
The term "parallel definitions" is used without specifying exactly which operations must be repeated and which remain common;
The designations of the various measured quantities coincide;
The designations of the quantities included in the formula for calculating the result of the analysis are not deciphered;
There are no requirements for formatting the analysis result.
7.6.4 It is not the task of the expert to eliminate grammatical errors and stylistic inaccuracies present in the document at the ICCA.
7.7 Validation of metrological terms
7.7.1 Metrological terms must comply with GOST R 1.12 and.
7.7.2 In ICCA documents, the terms “analyzed”, “determined”, “measurable”, “controlled” are often used as synonyms, which creates uncertainty in interpretations. When drawing up conclusions, it is advisable for experts to use the following set phrases:
Analyzed sample, analyzed substance (material), object of analysis;
The component being defined;
Measured value;
Controlled parameter, control standard.
7.7.3 In the regulation of the ICCA, which provide for the repeated execution of a sequence of operations, it becomes necessary to use two terms, one of which applies to a single sequence of operations, the other - to the totality of such sequences. In such cases, combinations of terms are used: “observation and measurement”, “single measurement” and “two (three) multiple measurements”, “single measurement” and “multiple measurement” (if the number of measurements is four or more), “single determination” (or "definition") and "analysis". It is necessary to pay attention to the fact that only one of the specified (or similar in meaning) combinations of terms is used in the ICCA document.
7.7.4 The examiner should take into account that chemical analysis often acts as a step in the testing or control procedure, and therefore the relevant terms may be used in the ICCA document. In particular, the measured value can be interpreted as an indicator of product quality, and the result of measurements (analysis) - as a test result or indicator value.
The form of the register of documents received for metrological examination
|
Applicant |
Date of receipt of documents |
List of received documents |
Date of request for additional documents |
Date of receipt of additional documents |
List of additional documents received |
Experts |
Date of approval of the expert opinion |
Additional documents request formHead ________________________________ applicant enterprise REQUEST Based on the results of the preliminary metrological examination _________ number (index) and name of the document (draft document) in which the ICAC is regulated I propose to send to __________________________________ before ________________ name GNMC the following additional documents: _______________________________________ ________________________________________________________________________ The examination is carried out in accordance with _______________________________________ number and date of the letter (contract) Contact phone _____________________ Deputy Director of the SSMC __________________ ____________________________ signature full name |
Form of expert opinion 1)_________________________________________________________________________ __________________________________ organization conducting the review APPROVE ____________________________________ job title ___________ _____________________ signaturedecryption signature ___________________ date CONCLUSION according to the results of metrological examination of the method of quantitative chemical analysis 1), regulated in _____________________________________________________, number (index) and name of the document (draft document), ________________________________________________________________________ organization-developer, its address certified 2) _________________________________________________________ organization that certified the methodology, certificate number The examination was carried out on the basis of __________________________________________ number of the letter (contract), _________________________________________________________________________ organization that submitted the ICCA for examination Additional materials provided by the expert: ________________________ technical task, _________________________________________________________________________ certificate of attestation, reports, protocols, etc. Methodology (Not) designed for use in the areas of distribution of state metrological control and supervision. Conclusions on the compliance of the MKCA with the requirements of GOST R 8.563-96 “State system for ensuring the uniformity of measurements. Measurement methods": a) Names of measured quantities and designations of their units ( with the exception of those indicated in remarks no. ________) meet the requirements of GOST 8.417-81 “State system for ensuring the uniformity of measurements. Units of physical quantities”, ________________________________________________________________ _________________________________________________________________________ other documents b) Choice of measuring instruments ( with the exception of those indicated in remarks No. _______ _) satisfies the conditions of the measurement problem and can be recognized as rational. Types of selected measuring instruments, including standard samples( _____), approved by the State Standard of Russia 3) . c) Measuring range 4) ( Not) meets the requirements of __________________________ technical task, ______________________________________________ (see also note no. ___) 5) . specifications, standard, etc. d) Measurement error characteristics ( Not) comply _________ ____________________________________________ (see also note no. _____) 6) . terms of reference, specifications, standard, etc. e) Measurement accuracy control procedures ( Not) are provided; control standards are linked ( not linked) with measurement error characteristics ( see also note no. _____). e) Requirements, rules and operations ( with the exception of those indicated in remarks no. _____) are presented with sufficient completeness to obtain measurement results, the error of which does not exceed the established limits 7). g) Metrological terms ( with the exception of those indicated in remarks no. _____) correspond to GOST R 1.12-99 “State standardization system of the Russian Federation. Standardization and related activities. Terms and Definitions” and “State System for Ensuring the Uniformity of Measurements. Metrology. Basic terms and definitions”. And) ______________________________________________________________________ other expert assessments Remarks Expert ( s): ________________________________________________________________________ positionsignaturesignature transcript __________ 1 ) Option "Measurement methods". 3) They are given only for the MKCA, intended for use in the areas of distribution of state metrological control and supervision. 4) Variant: "range of measured values". 5) Option: "measurement range not set". 6) Option: "characteristics of the measurement error have not been established." 7) Option: "... established limits." |
Examples of block diagrams of the MKHA
OP- alloy sampling; measure the masses t 1 And t 2, G.
P- sample preparation: dissolution by heating, cooling, dilution.
AND- potentiometric titration of silver with sodium chloride solution,V 1 And V 2 - volumes of solution used for titration, cm 3 .
VR-calculation of the results of determinations; T Na C l / Ag - titer of sodium chloride solution for silver, g/cm 3 ; X 1 And X 2- mass fraction of silver in samples, %.
Control of the convergence of the results of determinations and calculation of the average value of the mass fraction of silver in the alloyXcR(result of analysis).
Alloy test.
titratable solution.
Figure D.1 - Block diagram of the technique for measuring the mass fraction of silver in alloys
OP- gas sampling; during sampling, sample parameters are measured: temperature T, ° WITH; Atmosphere pressure r a, kPa; underpressureDR, kPa; selection timet , min; volume flowQ, dm 3 /min.
PP- extraction of methanol from a gas sample using a sorption tube.
E- extraction of methanol and measurement of the volume of the extractVuh, cm 3 .
AND-introduction of three aliquots of the extract into the evaporator of the chromatograph and obtaining analytical signalsS 1 , S 2 , S 3 .
Monitoring the convergence of analytical signals and calculating the average valueS.
PV- preliminary calculation; Cm- mass concentration of methanol in the extract, mg/cm 3 .
VR- calculation of the measurement result; Hm- mass concentration of methanol in a gas sample at a temperature of 273 K and a pressure of 101.3 kPa, mg/m 3 .
PGR-1 - preparation of calibration solution 1 with mass concentration of methanol, mg/cm 3 .
Lines (2), (3), (4) correspond to calibration solutions 2, 3, 4.
Calculation of calibration coefficients for solutions 1-4, control of convergence of coefficients and calculation of average TO.
Gas sample/
Sorbent with methanol.
Extract and calibration solution
Figure D.2 - Structural diagram of the technique for measuring the mass concentration of methanol in gas emissions by the chromatographic method
Rabinovich S.G. Measurement errors. - L .: Energy, 1978
Semenko N.G., Panova V.I., Lakhov V.M. Standard samples in the system for ensuring the uniformity of measurements. - M.: Publishing house of standards, 1990
Kateman G., Piipers F.V. Quality control of chemical analysis. - Chelyabinsk: Metallurgy, 1989
Dörfel K. Statistics in analytical chemistry. - M.: Mir, 1994
Buytash P., Kuzmin N.M., Leistner L. Quality assurance of chemical analysis results. - M.: Nauka, 1993 RD 50-160-79 Implementation and application of GOST 8.417-81 “State system for ensuring the uniformity of measurements. Units"
OST 52.04.11-82 Atmospheric ozone. Terms, letter designations and definitions of basic quantities
RD 50-674-88 Guidelines. Metrological support for quantitative chemical analysis. Basic provisions
[ 22 ] MI 2377-98 Recommendation. State system for ensuring the uniformity of measurements. Development and certification of measurement methods
[ 27 ] MI 2083-90 Recommendation. State system for ensuring the uniformity of measurements. Measurements are indirect. Determination of measurement results and estimation of their errors
MI 2232-2000 State system for ensuring the uniformity of measurements. Ensuring the efficiency of measurements in process control. Error Estimation with Limited Initial Information
Quantifying uncertainty in analytical measurements. Document Translation EURACHEM. - St. Petersburg: Christmas, 1997
[ 33 ] MI 2552-99 Recommendation. State system for ensuring the uniformity of measurements. Application of the "Guidelines for the expression of measurement uncertainty"
[ 34 ] MI 2335-95 Recommendation. State system for ensuring the uniformity of measurements. Internal quality control of the results of quantitative chemical analysis
[ 37 ] MI 1992-98 Recommendation. State system for ensuring the uniformity of measurements. Metrological certification of standard samples of the composition of substances and materials according to the preparation procedure. Basic provisions
Key words: method of quantitative chemical analysis, metrological examination, state scientific metrological center, analyzed object, determined component, measured value, measuring instrument, measurement result error characteristic
In practice, all the achievements of analytical chemistry as a science are realized in its final product - chemical analysis technique specific object.
There are methods of qualitative chemical analysis and methods of quantitative chemical analysis of the substance of the object of analysis. Qualitative and quantitative chemical analysis procedures can be described sequentially in one method.
Method of chemical analysis substances of the object of analysis - a document in which, in accordance with the method of analysis used, a sequence of operations and rules is described, the implementation of which ensures obtaining chemical analysis result a specific substance of a specific object of analysis with established error characteristics or uncertainty for methods of quantitative analysis, and for methods of qualitative analysis - with established reliability.
The result of chemical analysis can be presented, for example, as follows: according to the method of qualitative analysis, by conducting qualitative reactions, it was established that with a 100% certainty there is iron in the sample of the ore substance of the Bakcharskoe deposit; according to the method of quantitative analysis by dichromatometry, it was established that the iron content in the sample of the ore substance of the Bakcharskoe deposit is (40 ± 1)% with a confidence level of 0.95.
Each method of chemical analysis is based on the use of any one method of chemical analysis.
Examples of names of chemical analysis methods:
Method for measuring the mass concentrations of cadmium, copper and lead ions in drinking, natural and waste waters by stripping voltammetry .
Methodology for performing measurements of mass concentration polychlorinated dibenzo-p-dioxins and dibenzofurans in atmospheric air samples by chromato-mass spectrometry.
Method for measuring the mass fraction of heavy metals in soils and soils using X-ray fluorescence analyzers of the X‑MET type, METOREX (Finland).
Chemical analysis of a substance is a complex multi-stage process, it is carried out in a certain sequence, which is usually described in the analysis methodology specific object.
The analysis of any samples of a substance, including samples of the substance of environmental objects, is carried out in a certain sequence of its stages:
1. Sampling of a substance (in the field in ecology);
2. Obtaining a representative laboratory and analytical sample of the analyte;
3. Preparation of the sample of the analyte for the measurement of the analytical signal;
4. Creation of conditions for measurements and preparation of measuring instruments;
5. Preparation of the reference substance (standard);
6. Carrying out direct measurements of the analytical signal of standards and preparing a method for comparison with the standard when applying physical methods of analysis;
7. Carrying out direct measurements of the analytical signal of the analyzed sample of the substance;
8. Processing the results of direct measurements - identification of components and calculation of the content of the analyte in the sample of the analyte (indirect measurements);
9. Evaluation of the acceptability of the chemical analysis result by checking its precision (repeatability, reproducibility) and correctness;
10. Registration of the results of the chemical analysis of the sample of the substance of the object of analysis.
The ecologist is obliged to use the services analytical laboratories, accredited for the right to perform chemical analysis of environmental substances An accredited laboratory is considered to be a legally independent laboratory whose employees have repeatedly confirmed their technical competence. The methodology should be classified as a national (GOST) or industry (OST) standard or industry document (RD, PND F).
An example of requirements for organizational documents for the protection of atmospheric air in the laboratory of an enterprise to control the negative impact on the environment. The laboratory must have the following documents:
Regulations on the laboratory, its passport;
Documents on accreditation (attestation);
Certificates of verification of measuring instruments by state metrological authorities
Passports for state standard samples of the composition and properties of controlled objects;
Results of internal and external quality control of performed measurements;
Sampling acts and logs of their registration;
Certified measurement methods;
Logs of the results of environmental impact monitoring.
The result of a quantitative chemical analysis of a sample of a substance, including an ecological object, is expressed through mass fraction w (A) or mass concentration of the determined component A, C m (A).
An ecologist, for example, when assessing the pollution of a substance of environmental objects, submits for chemical analysis to an analytical laboratory selected samples of solid, liquid, gaseous, or heterophase substances weighing up to 1 kg. He is interested in the complete chemical composition or the content of one or more components (in the form of atoms, isotopes, ions, molecules, or groups of molecules with the same properties) in the sample of the substance of the object of analysis - in soils, in plants, in bottom sediments, in natural waters , in atmospheric air and other ecological objects.
Mass fraction w (A) component A is the ratio of mass m (A) component A, of the substance present in the sample to the total mass of the sample of the substance m (thing), which went to the analysis:
w (A) \u003d m (A) / m(item), w / r
Mass fraction of the component A in a sample of a substance can be converted into its percentage:
w (A) \u003d × 100,%
Volume fraction of the liquid component A in a sample of a liquid substance or gaseous component A in a sample of a gaseous substance is calculated as:
w (A) \u003d 100,%,
Where V (A) - volume of liquid or gaseous component A in total V total samples of a liquid or gaseous substance;
In international practice, they use the way of expressing the mass fraction as one part of a component into a large number of other parts:
parts per hundred , %, pph, g∙100/kg;
parts per thousand , ‰, ppt, g/kg;
parts per million , ppm, mg/kg, g/t;
parts per billion , ppb, μg/kg, mg/t;
To quantify the content of the component A in liquid and gaseous matter, the concept component concentration A.
Component A concentration (C(A)) is a value that characterizes the relative content of a given component in a multicomponent substance and is defined as the ratio of the number of component particles A(molar concentration of the component A, molar concentration of component equivalent A) or the mass of the component A ( mass concentration of the component A), related to a certain volume of liquid or gaseous substance.
The concentration of a component is always a named value, it makes sense for the component A specific name. This is also reflected in the definition of concentration, which emphasizes that we are talking about the relative content of a given component in the volume of a multicomponent liquid or gaseous substance.
The basic unit of measure for the number of particles of a component (n) in the International System of Units of Physical Quantities (SI system), adopted for use in the USSR in 1984, is 1 mol. 1 mol particles of any component that is of interest to us in the form of such structural chemical units as an atom (element), isotope, functional group, including an ion, or molecule, contains 6.022 × 10 23 such particles in any volume or mass of matter. thousandth part 1 mol(multiple unit) is denoted mmol ( read millimole).
Number of component particles A (n (A)) in any mass of the component A (m(A)) calculated by the formula:
n (A) \u003d m (A) / M (A), mol,
Where m (A) - component mass A, g; M (A) - relative molar mass of the component A, g/mol;
In the international system of units of physical quantities, according to GOST 8.417-2002 “GSI. Units of quantities", the main names for the concentration of components in the volume of a liquid or gaseous substance are molar concentration of the component, mol / m 3, And mass concentration of the component, kg / m 3.
Molar concentration of component A in solution – C m (A) - is the particle number content of the component A n (A) per unit volume V
C m (A) \u003d n (A) / V; or C m (A) \u003d m (A) / [M (A) V . ]
The molar concentration of a component is measured in mol / m 3; mol / dm 3, mmol / dm 3 mol/l.)
An example of a recording form in documents: C m (NaCl) \u003d 0.1 mol / dm 3 \u003d 0.1 mmol / cm 3 (in analytical practice for internal use and use the following form of recording: 0.1 M NaCl).
Both in analytical practice and in various types of professional activities, including ecology, concentration expressed in mass units is used.
Mass concentration of component A is the mass content m (A) component A per unit volume V liquid or gaseous substance, is calculated as:
C m (A) \u003d m (A) / V. ,
The mass concentration of the component is measured in kg / m 3; submultiple units are also used - g / m 3, g / dm 3, mg / dm 3 etc. (for intralaboratory use, a unit is allowed g/l, g/ml).
An example of a recording form: C m (NaCl) \u003d 0.1 g / dm 3, (in analytical practice for internal use the notation form C m (NaCl) \u003d 0.1 g / l \u003d 0.1 mg / ml is allowed).
Knowing the mass concentration of the component A in solution, you can calculate its molar concentration and vice versa.
C m (A) \u003d C m (A) / M (A), If C m (A) expressed in g / dm 3,
C m (A) \u003d C m (A) M (A), If C m (A) expressed in mol / dm 3.
Ways of expressing the concentration of a component in a solution and the relationship between different types of concentration are given in Annex 3.
In ecology, the content of determined components in samples of a liquid substance is usually expressed through mass concentration in units g / dm 3, mg / dm 3, mcg / dm 3, in samples of a gaseous substance - in units g / m 3, mg / m 3 μg / m 3.
The mass of the sample m (thing) can be measured with the required accuracy on an analytical balance, the volume V can be measured with the required accuracy using measuring utensils. Weight of the component A, m (A), or the number of particles of the component A, n (A), it is impossible to directly measure the substances in the sample, they can only be measured indirectly (calculated using the appropriate formula, found from the calibration graph). To this end, various methods of quantitative chemical analysis.
The normative document for the measurement method should regulate how many (one or more) single observations should be made, how they are averaged (arithmetic mean of the results of multiple observations, median or standard deviation) and how they are presented as a measurement result (or test result). It may be necessary to introduce standard corrections (for example, such as bringing the volume of gas to normal temperature and pressure). Thus, the result of measurements (tests) can be presented as a result calculated from several observed values. In the simplest case, the result of measurements (tests) is actually the observed value).
According to "PMG 96-2009 GSI. Results and characteristics of measurement quality. Representation forms”, the measurement result is represented by a named or unnamed number. Together with the measurement result, the characteristics of its error or their statistical estimates are presented. The presentation of measurement results obtained as the arithmetic mean of the results of multiple observations is accompanied by an indication of the number of observations and the time interval during which they were carried out.
The accuracy of the chemical analysis result. Standards for monitoring the accuracy of the result of measuring the content of the controlled component in the sample of the analyte, procedures and frequency of control
According to “GOST R ISO 5725-1-2002 Accuracy (correctness and precision) of measurement methods and results. Part 1. Basic Provisions and Definitions”:
accuracy –With the degree of closeness of the measurement result to the accepted reference value.
accepted reference value - the value that serves as the match for comparison and is obtained as:
a) a theoretical or established value based on scientific principles;
b) an assigned or certified value based on the experimental work of some national or international organization;
c) an agreed or validated value based on collaborative experimental work led by a scientific or engineering team;
d) the expected value of the characteristic being measured, i.e. the mean value of a given set of measurement results - only if a), b) and c) are not available.
The term "accuracy", when referring to a series of measurement (test) results, includes a combination of random components and a total systematic error.
right - the degree of closeness of the average value obtained from a large series of measurement results (or test results) to the accepted reference value. Notes: The indicator of correctness is usually the value of the systematic error.
systematic error is the difference between the mathematical expectation of the measurement results and the true (or, in its absence, the accepted reference) value. Notes: The true value of the quantity is unknown, it is used only in theoretical studies.
As components of the systematic measurement error, a non-excluded systematic error is distinguished, which is a component of the systematic measurement error due to the imperfection of the implementation of the accepted measurement principle, the calibration error of the measuring instrument used), etc.
precision - the degree of closeness to each other of independent measurement results obtained repeatedly in specific regulated conditions. Notes: Precision depends only on random errors and has nothing to do with the true or stated value of the measured quantity. A measure of precision is usually expressed in terms of uncertainty and is calculated as the standard deviation of the measurement results. Less precision corresponds to a larger standard deviation. "Independent results of measurements (or tests)" means results obtained by a method that is not influenced by any previous result obtained from testing the same or similar object. Quantitative values of precision measures significantly depend on the regulated conditions. The extreme cases of sets of such conditions are the repeatability conditions and the reproducibility conditions.
repeatability (synonym convergence) is the precision under repeatability conditions.
repeatability (convergence) conditions- conditions under which independent measurement (or test) results are obtained repeatedly by the same method on identical test objects, in the same laboratory, by the same operator, using the same equipment, within a short period of time .
reproducibility – precision under reproducibility conditions.
reproducibility conditions – conditions under which measurement (or test) results are obtained repeatedly by the same method, on identical test objects, at different times, in different laboratories, by different operators, using different equipment, but reduced to the same measurement conditions (temperature, pressure, humidity, etc.).
Measurement result accuracy control standards are indicators of repeatability (convergence), reproducibility and correctness of the measurement result.
Our laboratory offers a wide range of analyzes required for the following works:
Environment monitoring
Passportization of waste (development of a hazardous waste passport)
Determination of the component composition of production waste
· Calculation of waste hazard class
· Analysis of water, air, products, etc.
When developing a passport for hazardous waste, it is necessary to determine the composition of the waste. A mandatory document when agreeing on a waste passport is the CCA protocol (quantitative chemical analysis), which is done by our laboratory, which is accredited for this type of activity. The CSA protocol is drawn up after the analysis of the sample and contains information about the component composition of the waste.
The composition is indicated in mg/kg of dry matter and in % on dry matter. Also, the CCA protocol contains information on regulatory documents for the measurement procedure. In addition, the protocol of quantitative chemical analysis for hazardous waste contains information about the legal entity or individual entrepreneur (name of organization and legal address), as well as information about the laboratory that performed the analysis of the hazardous waste sample.
When drawing up documents for obtaining a license to carry out activities for the collection, use, neutralization, transportation, disposal of waste of hazard class I-IV, CCA protocols for hazardous waste are also required. In this case, the CCA protocols are used to indicate information about the composition of the wastes of I-IV hazard class declared in the license.
It is very important to take into account the assessment of the quality indicators of quantitative chemical analysis (QCA) methods when conducting QCA.
Protecting the environment from the increasing impact of chemicals is receiving increasing attention around the world. In our country, on the basis of the Law of the Russian Federation "On Ensuring the Uniformity of Measurements", environmental protection belongs to the sphere of state metrological control and supervision.
At the heart of all measures to prevent or reduce environmental pollution is the control of the content of harmful substances. Monitoring is necessary to obtain information about the level of pollution. The assessment of pollution of environmental objects is the maximum permissible concentration (MAC). Normalized MPCs should form requirements for the accuracy of pollution control and regulate the required level of metrological assurance of the state of the environment.
Quantitative chemical analysis (QCA) is the experimental determination of the mass or volume fraction of one or more components in a sample by physical, chemical and physico-chemical methods.
CCA is the main tool for ensuring the reliability of the results of the analysis of environmental objects.
A feature of CCA is that the composition of multicomponent systems is measured. The measurement of the composition is hampered by the effects of the mutual influence of the components, which determines the complexity of the chemical analysis procedure. Characteristic of analysis as a measuring process is that the analyte distributed in the sample matrix is chemically bound to the matrix components.
Other physico-chemical factors of the sample can also influence the result of the measurement and their accuracy. This leads to the need:
firstly, the normalization of the influencing quantities for each technique,
secondly, the use of certified substances that are adequate to the analyzed samples (at the stage of monitoring the accuracy of measurement results).
The main goal of metrological support of measurements in monitoring and controlling the environment is to ensure the unity and required accuracy of the measurement results of pollution indicators.
In the multifaceted and complex work to ensure the uniformity of measurements in the country, the most important place is given to the development and certification of measurement procedures (MPM). This is quite clearly evidenced by the fact that the Law of the Russian Federation "On Ensuring the Uniformity of Measurements" includes a separate Article 9, which reads: "Measurements must be carried out in accordance with the measurement procedures certified in the prescribed manner."
In connection with the introduction of GOST R ISO 5725-2002, changes were made to the state standard of the Russian Federation GOST R 8.563-96 "GSI. Methods for performing measurements", which determines the procedure for the development and certification of methods for performing measurements, including methods for quantitative chemical analysis (QCA). According to the requirements of this standard, organizations must have lists of documents for CCA methods used in the areas of distribution of state metrological control and supervision in this organization, as well as plans for the cancellation and revision of documents for CCA methods that do not meet the requirements of the standard. In addition, these plans should provide for certification and, if necessary, standardization of CCA methods.
The six GOST R ISO 5725-2002 standards detail and specifically (with examples) set out the main provisions and definitions of the accuracy indicators of measurement methods (MP) and measurement results, methods for experimental evaluation of accuracy indicators and the use of accuracy values in practice. Attention should be paid to the new terminology presented in the GOST R ISO 5725 standard.
In accordance with GOST R 5725-1-2002 - 5725-6-2002, three terms are used in describing the accuracy of CCA: precision, correctness and accuracy.
Precision - the degree of closeness to each other of independent measurement results obtained under specific specified conditions. This characteristic depends only on random factors and is not related to the true value or the accepted reference value.
Accuracy - the degree of closeness of the result of the analysis to the true or accepted reference value.
The reference value is the value that serves as the negotiated value. As a reference value can be taken:
theoretical or scientifically established value;
certified value of CO;
certified value of the mixture (AS);
The mathematical expectation of the measured characteristic, i.e. the mean value of a given set of analysis results.
Various factors can influence the variability of the result of a chemical analysis: time (time interval between measurements), calibration, operator, equipment, environmental parameters.
Depending on the influencing factors, the precision of the analysis results includes:
Precision analysis under repeatability conditions - conditions under which the results of the analysis are obtained by the same method in the same laboratory, by the same operator using the same equipment, almost simultaneously (parallel determinations);
· Precision of the analysis under conditions of reproducibility - the conditions under which the results of the analysis are obtained by the same method in different laboratories, varying by various factors (different time, operator, environmental conditions);
· intralaboratory precision of the analysis - the conditions under which the results of the analysis are obtained by the same method in the same laboratory with the variation of various factors (time, operator, different batches of reagents, etc.).
The measure of precision is the standard deviation (RMS):
r - frequency standard deviation;
R - RMS of reproducibility;
Rl - standard deviation of intralaboratory precision).
RMS characterizes the spread of any result from a series of observations relative to the average result of the analysis () and is denoted by S.
Sample S is calculated by the formula:
where i is the result of i - definitions;
- arithmetic mean of the results of parallel determinations;
N is the number of parallel definitions.
The assessment is made by the sample standard deviation S ~ S ,
where is the general set of measurement results.
The qualitative characteristics of the methods and results of the analysis are: accuracy, repeatability, intralaboratory precision, reproducibility, correctness.
It is important for the laboratory to evaluate the quality of the results of the analysis obtained using the technique over a long period of time. With the accumulation of statistical material based on the results of intralaboratory control, it is possible, in accordance with GOST R ISO 5725-6, RMG 76-2004, to control the stability of the standard deviation (RMS) of repeatability, the standard deviation (RMS) of intermediate precision, and the accuracy indicator using Shewhart charts. Stability control is carried out for each composition indicator analyzed in the laboratory in accordance with the applied methodology. Moreover, the control of the stability of the correctness is carried out only for those indicators for which there are sufficiently stable means of control in the form of GSO, OSO, SOP, AS or calibration solutions.
In accordance with the selected algorithm for conducting control procedures, the results of control measurements are obtained and control procedures are formed. Control charts can be built closer to the beginning, middle and end of the range of measured concentrations.
The stability of the RMS of repeatability, RMS of intermediate precision, and accuracy index is evaluated by comparing the discrepancies obtained for a certain period of the results of the analysis of the controlled indicator in the sample with those calculated when building control charts with warning and action limits. The results of stability control using Shewhart control charts are given in GOST R ISO 5725-6.
The measurement technique is considered as a set of operations and rules, the implementation of which ensures the receipt of measurement results with a known error. The guarantee of measurement error is the main, decisive feature of the MVI. Previously, in accordance with the requirements of regulatory documents, each analysis result was assigned an error calculated during the metrological study of the methodology and assigned to the methodology during its certification. GOST R ISO 5725-2002 introduces an additional concept - laboratory error. Thus, the laboratory has the right to evaluate its error for each MVI, and it should not exceed the assigned one and, in accordance with RMG 76-2004, draw up a protocol of established quality indicators for the analysis results when implementing the analysis methodology in the laboratory.
In addition, earlier, to assess the metrological characteristics of analytical measurements of the content of a component in the objects under study, it was sufficient to conduct an intralaboratory experiment. The modern regulations for the certification of quantitative chemical analysis methods prescribe an interlaboratory experiment with the participation of at least eight laboratories under identical measurement conditions (the same methods, homogeneous materials). Only in the case of a metrological study of methods requiring unique equipment, statistical processing of the results of an intralaboratory experiment is allowed.
The methodology must necessarily indicate the characteristics of the error and the values of the repeatability limits (if the methodology provides for parallel determinations) and reproducibility. In the most extreme case, at least one of the components of the error, or the total error, must be indicated. If this is not the case, then the methodology cannot be applied and references to it are not allowed.
But at the same time, in accordance with the requirements of RMG 61-2003, if it is impossible to organize an experiment in different laboratories, it is allowed to obtain experimental data in one laboratory under conditions of intralaboratory precision, varying by as many different factors as possible. In this case, the reproducibility index of the analysis technique in the form of a standard deviation is calculated by the formula:
R = k S Rl,
where SRl is the sample standard deviation of the analysis results obtained under conditions of intralaboratory precision;
k is a coefficient that can take values from 1.2 to 2.0.
In accordance with GOST R 8.563-2009, methods that are intended for use in the field of distribution of state metrological control and supervision must be certified and entered in the Federal Register. The institutions eligible for certification are:
All-Russian Research Institute of Metrology and Certification (VNIIMS),
Ural Research Institute of Metrology (UNIIM),
All-Russian Research Institute of Metrology (VNIIM) named after V.I. Mendeleev (Center for Research and Control of Water Quality (TSIKV, St. Petersburg),
Hydrochemical Institute of the Federal Service for Hydrometeorology and Environmental Monitoring, CJSC "ROSA" (Moscow).
The All-Russian Scientific Research Institute of Metrology and Certification (VNIIMS) is responsible for the state registration of certified methods and for the observance of the copyrights of the developer organization.
Methods that are not used in the areas of distribution of state metrological control and supervision are certified in the manner established at the enterprise. If the metrological service of the enterprise is accredited for the right to perform certification of methods, then it can carry out metrological examination of methods that are used in the field of distribution of state metrological control and supervision.
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