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Guideline on validation of test methods for food and cosmetics of import and export - Part 2: Chemical method
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Basic data
| Standard ID | SN/T 5326.2-2020 (SN/T5326.2-2020) |
| Description (Translated English) | Guideline on validation of test methods for food and cosmetics of import and export - Part 2: Chemical method |
| Sector / Industry | Commodity Inspection Standard (Recommended) |
| Classification of Chinese Standard | X04 |
| Word Count Estimation | 13,192 |
| Date of Issue | 30/12/2020 |
| Date of Implementation | 1/7/2021 |
| Regulation (derived from) | Announcement No. 136 (2020) of the General Administration of Customs |
| Issuing agency(ies) | General Administration of Customs |
SN/T 5326.2-2020: Guideline on validation of test methods for food and cosmetics of import and export - Part 2: Chemical method
---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/SNT5326.2-2020
Guideline on validation of test methods for food and cosmetics
of import and export
Part 2: Chemical method
Preface
The standard “Validation Procedures of Professional Analysis Methods for Import and Export Food and
Cosmetics Products” consists of the following 6 parts:
— Part 1: General guideline
— Part 2: Chemical methods
— Part 3: Traditional microbiological methods
— Part 4: Molecular biology methods
— Part 5: Immunological methods
— Part 6: Radioactive analysis methods
This section is the Part 2 of the series of standards written in accordance with the rules given in GB/T 1.1— 2009
“Standardization Guidelines Section 1: Standard Structure and Writing Rules”.
Please note that some contents of this section may involve patents and the publishing department of this section
is responsible for identifying these patents.
This part is proposed and managed by General Administration of Customs, People’s Republic of China.
This part was drafted by the following institutions: Shenzhen Inspection and Quarantine Research Institute,
Shenzhen Customs District P. R. China, Shanghai Customs District P. R. China, Nanjing Customs District P. R.
China, Tianjin Customs District P. R. China, Fuzhou Customs District P. R. China, Hangzhou Customs District P.
R. China, and Hefei Customs District P. R. China.
This part was mainly drafted by the following people: Zhenfeng Yue, Chengui Xiao, Feng Xiao, Jian Zhu, Tao
Ding, Wenjie Zheng, Fang Yang, Qinting Jiang and Fang Han.
Guideline on validation of test methods for import and export food
and cosmetics
Section 2: Chemical methods
1 Scope
Section II provides guidelines for validating the standard chemical analysis methods. It is the specific
requirements and supplementation of validating the standard chemical analysis methods in Section I.
This section is suitable for validating the methods used in the process for establishing the standard chemical
analysis methods regardless they are new ones, revised ones, or the ones equivalent to or the adopted revisions
of the international standards. In addition, when the laboratory adopts non-standard methods and independently
developed new methods, it can also refer to this procedure to validate the applicability of these methods.
2 Normative references
The following documentations are indispensable for the application of this guideline. For all dated references,
only the dated version applies to this guideline. For all undated references, the latest version (including all
amendments) applies to this guideline.
GB/T 6379.1— 2014 Accuracy of measurement methods and results (trueness and precision), Part I: General
Rules and Definitions
GB/T 27417— 2017 Conformity assessment: Guideline on Confirmation/Validation of Chemical Analysis
Methods
GB/T 32467— 2015 Chemical Analysis Methods Confirmation/Validation and Internal Quality Control: Terms
and Definitions
SN/T 0001— 2016 Basic Rules of Standard Physical and Chemical Measurement Methods for Import and Export
Foods and Cosmetics
CNAS-GL03 Guideline for Evaluating Homogeneity and Stability of the Validation Sample
3 Terms and definitions
The terms and definitions defined in GB/T 6379.1—2004, GB/T 32467—2015, GB/T 27417—2017, SN/T
0001— 2016 and the following apply to this document.
3.1 Qualitative methods are the analytical methods for substances identification based on their chemical,
biological or physical properties [GB/T 27417— 2017, Definition 3.5]
3.2 Quantitative methods are the analytical methods for determining the mass or mass fraction of an analyte.
The results can be expressed as numerical values in appropriate units [GB/T 27417— 2017, Definition 3.6]
3.3 Screening methods are the methods able to efficiently process a large qantity of samples and determine the
presence or absence of a substance or a group of substances at the concentration level of interest [GB/T 27417—
2017, Defination 3.8]
3.4 Confirmatory methods are the methods that can provide all or part of the target’s information. Based on the
information, one can qualitatively or if necessary, quantitatively determine the presence or absence of certain
substances at the level of interest [GB/T 27417— 2017, Definition 3.7].
3.5 Specificity/selectivity is the ability of a method to distinguish a target analyte from other compounds such
as other analytes, matrix components and other possible interferents in the sample.
3.6 Limit of detection (LOD) is the minimum concentration at which an analyte can be detected, that is, within
a certain confidence, the minimum concentration of the analyte in the sample can be qualitatively detected using
a certain method [SN/T 0001— 2016, definition 3.1].
3.7 Limit of quantification (LOQ) is the lowest concentration or the lowest amount at which the measured
component of the sample can be quantified. The analysis results should ensure a certain degree of accuracy and
precision [GB/T 27417— 2017, definition 3.14].
3.8 Permitted limit (PL) is the material limit specified and required for a quantitative property such as
the maximum residue limit, highest permitted concentration or other maximum permitted amount, etc. [GB/T
27417— 2017, definition 3.9].
3.9 Level of interest is a decisive concentration such as permitted limit concentration for determining whether
a substance or analyte in the sample meets the regulations and requirements [GB/T 27417— 2017, definition
3.10].
3.10 Determination range is the interval between the highest and lowest concentrations or amounts of an
analyte in a sample that the method can quantify under certain trueness and precision.
3.11 Trueness is the degree of agreement between the average obtained from a large number of test results and
the accepted reference value [GB/T 6379.1— 2004, definition 3.7].
3.12 Precision is the degree of consistency between independent test results under the specified conditions [GB/
T 6379.1— 2004, definition 3.12].
3.13 Repeatability is the precision under repetitive conditions [GB/T 6379.1— 2004, definition 3.13].
3.14 Repeatability condition is the test condition for the same object in independent tests operated by the same
operator using the same equipment in the same laboratory within a short period [GB/T 6379.1— 2004, definition
3.14].
3.15 Reproducibility is the precision under reproducible conditions [GB/T 6379.1— 2004, definition 3.17].
3.16 Reproducibility condition is the test condition for the same object in independent tests operated by
different operators using different equipment in different laboratory [GB/T 6379.1— 2004, definition 3.18].
3.17 Ruggedness/robustness is the sensitivity of an analytical method to small changes in laboratory conditions
that generally are unable to deliberately controlled or maintained to be completely consistent [GB/T 32467—
2015, definition, 9.15].
3.18 Certified reference materials (CRMs) are materials with one or more properties able to be traced back
using a traceability procedure to the measurement units that are accurately reproduced to represent the specific
property and each standard value is accompanied by an uncertainty at a given level of confidence.
3.19 Matrix is the materials or components that are not analytes for analytical studies [SN/T 0001— 2016,
definition 3.10].
4 Provisions of performance parameters of the analysis methods
4.1 Selection of validation parameters
4.1.1 Method drafting party shall select appropriate parameters based on the intended use of the developed
method and establish a laboratory validation program. Typical validation parameters include specificity,
limit of detection, limit of quantification, determination range, sensitivity, robustness, trueness and precision,
repeatability and reproducibility. For different types of chemical detection methods, the selected validation
parameters are shown in Table 1.
4.1.2 For qualitative methods, intra-laboratory validation and independent laboratory validation parameters
should include at least the method’s specificity, limit of detection, robustness, and other technical parameters
and inter-laboratory validation parameters should include at least the method’s limit of detection and specificity.
4.1.3 For quantitative methods, intra-laboratory validation and independent laboratory validation parameters
should include at least the method’s specificity, limit of detection, limit of quantification, determination range,
trueness, repeatability, robustness and other technical parameters and inter-laboratory validation parameters
should include at least the method’s limit of quantification, determination range, trueness and reproducibility.
4.2 Specific specifications for performance parameters of chemical analysis methods
The specific specifications for performance parameters of chemical analysis methods can be found in SN/T
0001— 2016.
5 Validation of performance parameters of chemical analysis methods
5.1 Preparation of samples used for validation
5.1.1 For testing the applicable sample matrices and testing compounds that meet the requirements of the
validation technique, (for example that only a few types of testing sample matrices and compounds are suitable
for the validation methods and stable enough to satisfy the long-haul cold chain transport requirements), the
validation samples can be prepared as follows:
a) The method drafting party shall prepare the validation samples, homogenize the samples, and test their
homogeneity and stability. The homogeneity and stability evaluation shall be conducted referring to
CNAS-GL03. After the test is completed, the evaluation results should be submitted to the secretariat
and the secretariat will organize the experts to review the results.
b) Sample level: For a sample matrix, it is generally required to use 5 different levels of sample. In
addition, the type and number of samples for inter-laboratory validation also depend on the difficulty
and cost of sample obtaining, processing, and distribution as well as the time and cost required to
conduct the test. The sample selection should ensure that it represents those samples can be normally
measured and that the intended use of the method should be fulfilled. An inter-laboratory validation
test should select a minimum of 3 samples to represent different test levels and contain the lowest
concentration level (limit of quantification), concentration of interest and the highest concentration
level of the method’s determination range.
c) Number of samples: When deciding the number of samples required for the test, it should be
considered that operational errors occur occasionally when certain test results are obtained, and
additional samples are required. The number of samples to be prepared should be sufficient for the
test and allow for proper redundancy. However, providing too many samples should be avoid to prevent
excessively testing due to some reasons in a laboratory to “selectively” report certain test results,
thereby artificially increasing the precision of the laboratory test. Therefore, the number of samples is
usually 2-5 times of the amount of the required test samples.
d) The accepted reference value of the sample used in the process of trueness validation can be used as
the agreed true value. The standard sample could be: 1) a certified reference sample; 2) a sample
produced according to the purpose of known property test; and 3) a sample whose characteristics
are measured according to another measurement method with negligible bias. To assess the bias of a
standard test method, certified reference samples should be used whenever possible. In the cases that
the certified reference samples or control samples are unable to obtain or production of the certified
reference samples is particularly expensive, it is permitted to add a known concentration of reference
material into the blank sample matrix.
5.1.2 For the test method that applicable sample matrices and test compounds cannot meet the requirements
of the validation testing technology (the methods that require multiple types of sample matrices to be validated,
methods for many types of test compounds, methods for samples with poor stability, etc.), co-validation
laboratories are allowed to prepare standard addition samples according to the concentration levels specified
in the work instructions. However, the standard addition samples should be prepared at least 24 hours before
the test to ensure that the standard solution and the sample are fully adsorbed to mimic the actual sample state
as much as possible. For a sample matrix, at least 3 concentration levels should be added including the lowest
concentration level (limit of quantification), concentration level of interest, and the highest concentration level
of the method’s determination range.
5.2 Validation of method performance parameters
5.2.1 Specificity
5.2.1.1 Validation requirements
The specificity should be investigated during the establishment of methods such as residue analysis, component
identification, impurity detection, and principal component determination. It is advisable to use a variety of
samples to study the specificity of the method including the pure target analyte and the mixture with a complex
matrix. In each case, the separation of the studied analyte should be determined and the effects of suspicious
interference should be fully explained. If the specificity of the adopted method does not meet the requirements
of the test, multiple methods should be used to supplement it. Any limitation on method specificity should be
documented.
5.2.1.2 Validation methods
5.2.1.2.1 Specificity of residue analysis methods
For residue analysis methods, the ability to distinguish between target analytes and similar substances (isomers,
metabolites, degradation products, endogenous substances, matrix components, etc.) is crucial. In general,
interference should be examined using the following two methods in combination: a) Analyze a certain number of
representative blank samples to check for interference (signals, peaks, etc.) in the area where the target analyte
appears; b) Add a certain concentration of qualitative and/or quantitative substances that may interfere with the
analyte into the representative blank samples.
5.2.1.2.2 Specificity of component identification methods
The component identification methods should be able to distinguish compounds that may have similar structures.
The discrimination process can be confirmed by testing the sample containing the analyte to obtain a positive
result and testing the sample without the analyte to obtain a negative result (eg., compared to the known
reference material). In addition, using the method to test similar substances or substances with structure similar
to the analyte should not yield a positive result. The selection of potential interferers should be based on the
reasonable scientific judgments with consideration of possible interfering substances.
5.2.1.2.3 Specificity of content and impurity determination methods
A s a purity and impurity content test, the adopted analysis method should ensure that the content of impurities
in the analyte can be detected, such as related substances, heavy metals, etc. Therefore, the analysis method is
required to have certain specificity. In the case where impurities are available, a certain amount of impurities
can be added to the test sample to prove that the impurities and coexisting substances can be separated and
detected at appropriate trueness and precision. In the cases where impurities are not available, specificity can be
determined by comparing the results with another method that has different principle of isolation or detection and
been validated, or that has high specificity.
For example, for chromatographic analysis, a representative chromatogram should be given to illustrate
the specificity of the method, and individual components should be identified in the figure. The typical
chromatographic separation should be examined at a suitable concentration level, and the method specificity
can be demonstrated by the degree of resolution of the two compounds that have been diluted to similar
concentrations. If necessary, the purity of the chromatographic peaks should be examined to show that the
chromatographic peaks of the test components do not contain other components. If the specificity of the method
does not meet the requirements, additional methods are required to demonstrate specificity. Other separation
methods should also be considered similarly.
5.2.2 Limit of detection
5.2.2.1 Validation requirements
For detection methods and qualitative detection methods that the presence of the target compound or the
permitted limit of the target compound in the sample is zero, the limit of detection of the method must be
validated. Many methods can be used for determining the limit of detection. To ensure the reliability and
reproducibility of the limit of detection, the validation procedure uses probabilistic statistics. When the
probability that a target substance is reliably detected in a certain sample matrix is above 95%, the level of
concentration is the limit of detection of the method for the sample matrix.
The limit of detection for each representative sample matrix needs to be independently validated.
5.2.2.2 Validation method
5.2.2.2.1 Based on the preliminary sensitivity of the methods learned during the development of the method,
the standard setter should prepare the certified reference materials, quality control samples, or standard addition
samples at a series of concentrations, and use the test procedures in the draft of standard method for testing. The
concentration level that can be effectively detected is used as the reference concentration. The concentration
of 1 time~2 times (eg. 1.5 times) of that level can be used as the reference limit of detection (LODR) to
independently detect more than 6 certified reference materials, quality control samples, or standard addition
samples. The test results are subjected to statistical analysis to obtain the standard deviation (SD).
5.2.2.2.2 In the case of testing 20 certified reference materials, quality control samples, or standard addition
samples at LODR-3SD, LODR and LODR+3SD levels, the level that 19 samples can be detected is the limit of
detection of the method. Table 2 shows an example of validation data for determining the limit of detection for
clenbuterol in pork using liquid chromatography-mass spectrometry/mass spectrometry.
5.2.2.2.3 If the above concentration level is set too high or too low, one needs to appropriately reduce or
increase the concentration of the reference limit of detection (LODR) and repeat step 5.2.2.2.2 until exactly 19
samples can be effectively detected at a concentration level.
...