GUIDELINES ON THE ELABORATION AND/OR REVISION OF CODES OF HYGIENIC PRACTICE FOR SPECIFIC COMMODITIES
PRINCIPLES FOR THE ESTABLISHMENT OF CODEX METHODS OF ANALYSIS
ANALYTICAL TERMINOLOGY FOR CODEX USE
PRINCIPLES FOR THE ESTABLISHMENT OR SELECTION OF CODEX SAMPLING PROCEDURES
The establishment of additional food hygiene requirements for specific food items or food groups should be limited to the extent necessary to meet the defined objectives of individual codes.
Codex Codes of Hygienic Practice should serve the primary purpose of providing advice to governments on the application of food hygiene provisions within the framework of national and international requirements.
The Revised Recommended International Code of Practice - General Principles of Food Hygiene (including the Guidelines for the Application of the Hazard Analysis Critical Control Point (HACCP) System) and the Revised Principles for the Establishment and Application of Microbiological Criteria for Foods are the base documents in the field of food hygiene.
All Codex Codes of Hygienic Practice applicable to specific food items or food groups shall refer to the General Principles of Food Hygiene and shall only contain material additional to the General Principles which is necessary to take into account the particular requirements of the specific food item or food group.
Provisions in Codex Codes of Hygienic Practice should be drafted in a sufficiently clear and transparent manner such that extended explanatory material is not required for their interpretation.
The above considerations should also apply to Codex Codes of Practice which contain provisions relating to food hygiene.
PURPOSE OF CODEX METHODS OF ANALYSIS
The methods are primarily intended as international methods for the verification of provisions in Codex standards. They should be used for reference, in calibration of methods in use or introduced for routine examination and control purposes.
METHODS OF ANALYSIS
(A) Definition of types of methods of analysis
(a) Defining Methods (Type I)
Definition: A method which determines a value that can only be arrived at in terms of the method per se and serves by definition as the only method for establishing the accepted value of the item measured.
Examples: Howard Mould Count, Reichert-Meissl value, loss on drying, salt in brine by density.
(b) Reference Methods (Type II)
Definition: A Type II method is the one designated Reference Method where Type I methods do not apply. It should be selected from Type III methods (as defined below). It should be recommended for use in cases of dispute and for calibration purposes.
Example: Potentiometric method for halides.
(c) Alternative Approved Methods (Type III)
Definition: A Type III Method is one which meets the criteria required by the Codex Committee on Methods of Analysis and Sampling for methods that may be used for control, inspection or regulatory purposes.
Example: Volhard Method or Mohr Method for chlorides
(d) Tentative Method (Type IV)
Definition: A Type IV Method is a method which has been used traditionally or else has been recently introduced but for which the criteria required for acceptance by the Codex Committee on Methods of Analysis and Sampling have not yet been determined.
Examples: chlorine by X ray fluorescence, estimation of synthetic colours in foods.
(B) General Criteria for the Selection of Methods of Analysis
(a) Official methods of analysis elaborated by international organizations occupying themselves with a food or group of foods should be preferred.
(b) Preference should be given to methods of analysis the reliability of which have been established in respect of the following criteria, selected as appropriate:
(iii) precision; repeatability intra-laboratory (within laboratory), reproducibility inter-laboratory (within laboratory and between laboratories)
(iv) limit of detection
(vi) practicability and applicability under normal laboratory conditions
(vii) other criteria which may be selected as required.
(c) The method selected should be chosen on the basis of practicability and preference should be given to methods which have applicability for routine use.
(d) All proposed methods of analysis must have direct pertinence to the Codex Standard to which they are directed.
(e) Methods of analysis which are applicable uniformly to various groups of commodities should be given preference over methods which apply only to individual commodities.
RESULT: The final value reported for a measured or computed quantity, after performing a measuring procedure including all subprocedures and evaluations.
1. When a result is given, it should be made clear whether it refers to:
· the indication [signal]
· the uncorrected result
· the corrected result
· and whether several values were averaged.
2. A complete statement of the result of a measurement includes information about the uncertainty of measurement.
SPECIFICITY: The property of a method to respond exclusively to the characteristic or analyte defined in the Codex standard.
1. Specificity may be achieved by many means: It may be inherent in the molecule (e.g., infrared or mass spectrometric identification techniques), or attained by separations (e.g., chromatography), mathematically (e.g., simultaneous equations), or biochemically (e.g., enzyme reactions). Very frequently methods rely on the absence of interferences to achieve specificity (e.g., determination of chloride in the absence of bromide and iodide).
2. In some cases specificity is not desired (e.g., total fat, fatty acids, crude protein, dietary fibre, reducing sugars).
ACCURACY (AS A CONCEPT): The closeness of agreement between the reported result and the accepted reference value.
The term accuracy, when applied to a set of test results, involves a combination of random components and a common systematic error or bias component. When the systematic error component must be arrived at by a process that includes random error, the random error component is increased by propagation of error considerations and is reduced by replication.
ACCURACY (AS A STATISTIC): The closeness of agreement between a reported result and the accepted reference value.
Accuracy as a statistic applies to the single reported final test result; accuracy as a concept applies to single, replicate, or averaged values.
TRUENESS: The closeness of agreement between the average value obtained from a series of test results and an accepted reference value.
1. The measure of trueness is usually expressed in terms of bias.
2. Trueness has been referred to as "accuracy of the mean".
BIAS: The difference between the expectation of the test results and an accepted reference value.
1. Bias is the total systematic error as contrasted to random error. There may be one or more systematic error components contributing to bias. A larger systematic difference from the accepted reference value is reflected by a larger bias value.
2. When the systematic error component(s) must be arrived at by a process that includes random error, the random error component is increased by propagation of error considerations and reduced by replication.
PRECISION: The closeness of agreement between independent test results obtained under stipulated conditions.
1. Precision depends only on the distribution of random errors and does not relate to the true value or to the specified value.
2. The measure of precision is usually expressed in terms of imprecision and computed as a standard deviation of the test results. Less precision is reflected by a larger standard deviation.
3. "Independent test results" means results obtained in a manner not influenced by any previous result on the same or similar test object. Quantitative measures of precision depend critically on the stipulated conditions. Repeatability and reproducibility conditions are particular sets of extreme conditions.
Repeatability [Reproducibility]: Precision under repeatability [reproducibility] conditions.
Repeatability conditions: Conditions where independent test results are obtained with the same method on identical test items in the same laboratory by the same operator using the same equipment within short intervals of time.
Reproducibility conditions: Conditions where test results are obtained with the same method on identical test items in different laboratories with different operators using different equipment.
When different methods give test results that do not differ significantly, or when different methods are permitted by the design of the experiment, as in a proficiency study or a material-certification study for the establishment of a consensus value of a reference material, the term "reproducibility" may be applied to the resulting parameters. The conditions must be explicitly stated.
Repeatability [Reproducibility] standard deviation: The standard deviation of test results obtained under repeatability [reproducibility] conditions.
1. Repeatability [Reproducibility] standard deviation is a measure of the dispersion of the distribution of test results under repeatability [reproducibility] conditions.
2. Similarly "repeatability [reproducibility] variance" and "repeatability [reproducibility] coefficient of variation" could be defined and used as measures of the dispersion of test results under repeatability [reproducibility] conditions.
Repeatability [Reproducibility] limit: The value less than or equal to which the absolute difference between two test results obtained under repeatability [reproducibility] conditions may be expected to be with a probability of 95%.
1. The symbol used is r [R].
2. When examining two single test results obtained under repeatability [reproducibility] conditions, the comparison should be made with the repeatability [reproducibility] limit r [R] = 2.8 sr[sR].
3. When groups of measurements are used as the basis for the calculation of the repeatability [reproducibility] limits (now called the critical difference), more complicated formulae are required that are given in ISO 5725-6:1994, 4.2.1 and 4.2.2.
INTERLABORATORY STUDY: A study in which several laboratories measure a quantity in one or more "identical" portions of homogeneous, stable materials under documented conditions, the results of which are compiled into a single document.
The larger the number of participating laboratories, the greater the confidence that can be placed in the resulting estimates of the statistical parameters. The IUPAC-1987 protocol (Pure & Appl. Chem, 66, 1903-1911(1994)) requires a minimum of eight laboratories for method-performance studies.
Method-Performance Study: An interlaboratory study in which all laboratories follow the same written protocol and use the same test method to measure a quantity in sets of identical test samples. The reported results are used to estimate the performance characteristics of the method. Usually these characteristics are within-laboratory and among-laboratories precision, and when necessary and possible, other pertinent characteristics such as systematic error, recovery, internal quality control parameters, sensitivity, limit of determination, and applicability.
1. The materials used in such a study of analytical quantities are usually representative of materials to be analyzed in actual practice with respect to matrices, amount of test component (concentration), and interfering components and effects. Usually the analyst is not aware of the actual composition of the test samples but is aware of the matrix.
2. The number of laboratories, number of test samples, number of determinations, and other details of the study are specified in the study protocol. Part of the study protocol is the procedure which provides the written directions for performing the analysis.
3. The main distinguishing feature of this type of study is the necessity to follow the same written protocol and test method exactly.
4. Several methods may be compared using the same test materials. If all laboratories use the same set of directions for each method and if the statistical analysis is conducted separately for each method, the study is a set of method-performance studies. Such a study may also be designated as a method-comparison study.
Laboratory-Performance (Proficiency) Study: An interlaboratory study that consists of one or more measurements by a group of laboratories on one or more homogeneous, stable, test samples by the method selected or used by each laboratory. The reported results are compared with those from other laboratories or with the known or assigned reference value, usually with the objective of improving laboratory performance.
1. Laboratory-performance studies can be used to support accreditation of laboratories or to audit performance. If a study is conducted by an organization with some type of management control over the participating laboratories - organizational, accreditation, regulatory, or contractual - the method may be specified or the selection may be limited to a list of approved or equivalent methods. In such situations, a single test sample is insufficient to judge performance.
2. a laboratory-performance study may be used to select a method of analysis that will be used in a method-performance study. If all laboratories, or a sufficiently large subgroup, of laboratories, use the same method, the study may also be interpreted as a method-performance study, provided that the test samples cover the range of concentration of the analyte.
3. laboratories of a single organization with independent facilities, instruments, and calibration materials, are treated as different laboratories.
Material-Certification Study: An interlaboratory study that assigns a reference value ("true value") to a quantity (concentration or property) in the test material, usually with a stated uncertainty.
A material-certification study often utilizes selected reference laboratories to analyze a candidate reference material by a method(s) judged most likely to provide the least-biased estimates of concentration (or of a characteristic property) and the smallest associated uncertainty.
APPLICABILITY: The analytes, matrices, and concentrations for which a method of analysis may be used satisfactorily to determine compliance with a Codex standard.
In addition to a statement of the range of capability of satisfactory performance for each factor, the statement of applicability (scope) may also include warnings as to known interference by other analytes, or inapplicability to certain matrices and situations.
SENSITIVITY: Change in the response divided by the corresponding change in the concentration of a standard (calibration) curve; i.e., the slope, si, of the analytical calibration curve.
This term has been used for several other analytical applications, often referring to capability of detection, to the concentration giving 1% absorption in atomic absorption spectroscopy, and to ratio of found positives to known, true positives in immunological and microbiological tests. Such applications to analytical chemistry should be discouraged.
A method is said to be sensitive if a small change in concentration, c, or quantity, q, causes a large change in the measure, x; that is, when the derivative dx/dc or dx/dq is large.
Although the signal may vary with the magnitude of c, or q,, the slope, si, is usually constant over a reasonable range of concentrations, si may also be a function of the c or q of other analytes present in the sample.
RUGGEDNESS: The ability of a chemical measurement process to resist changes in results when subjected to minor changes in environmental and procedural variables, laboratories, personnel, etc.
PURPOSE OF CODEX METHODS OF SAMPLING
Codex Methods of Sampling are designed to ensure that fair and valid sampling procedures are used when food is being tested for compliance with a particular Codex commodity standard. The sampling methods are intended for use as international methods designed to avoid or remove difficulties which may be created by diverging legal, administrative and technical approaches to sampling and by diverging interpretation of results of analysis in relation to lots or consignments of foods, in the light of the relevant provision(s) of the applicable Codex standard.
METHODS OF SAMPLING
(A) Types of Sampling Plans and Procedures
(a) Sampling Plans for Commodity Defects:
These are normally applied to visual defects (e.g. loss of colour, mis-graded for size, etc.) and extraneous matter. They will normally be attributes plans, and plans such as those included in the FAO/WHO Codex Alimentarius Sampling Plans for Prepackaged Foods (AQL 6.5)1 may be applied.
1 Codex Alimentarius: Volume 13.
(b) Sampling Plans for Net Contents:
These are sampling plans which apply to pre-packaged foods generally and are intended to serve to check compliance of lots or consignments with provisions for net contents.
(c) Sampling Plans for Compositional Criteria:
Such plans are normally applied to analytically determined compositional criteria (e.g., loss on drying in white sugar, etc.). They are predominantly based on variable procedures with unknown standard deviation.
(d) Specific Sampling Plans for Health-related Properties
Such plans are generally applied to heterogeneous conditions, e.g., in the assessment of microbiological spoilage, microbial by-products or sporadically occurring chemical contaminants.
(B) General Instructions for the Selection of Methods of Sampling
(a) Official methods of sampling as elaborated by international organizations occupying themselves with a food or a group of foods are preferred. Such methods, when attracted to Codex standards, may be revised using Codex recommended sampling terms (to be elaborated).
(b) The appropriate Codex Commodity Committee should indicate, before it elaborates any sampling plan, or before any plan is endorsed by the Codex Committee on Methods of Analysis and Sampling, the following:
(i) the basis on which the criteria in the Codex Commodity standards have been drawn up (e.g. whether on the basis that every item in a lot, or a specified high proportion, shall comply with the provision in the standard or whether the average of a set of samples extracted from a lot must comply and, if so, whether a minimum or maximum tolerance, as appropriate, is to be given);
(ii) whether there is to be any differentiation in the relative importance of the criteria in the standards and, if so, what is the appropriate statistical parameter each criterion should attract, and hence, the basis for judgement when a lot is in conformity with a standard.
(c) Instructions on the procedure for the taking of samples should indicate the following:
(i) the measures necessary in order to ensure that the sample taken is representative of the consignment or of the lot;
(ii) the size and the number of individual items forming the sample taken from the lot or consignment;
(iii) the administrative measures for taking and handling the sample.
(d) The sampling protocol may include the following information:
(i) the statistical criteria to be used for acceptance or rejection of the lot on the basis of the sample;
(ii) the procedures to be adopted in cases of dispute.
(a) The Codex Committee on Methods of Analysis and Sampling should maintain closest possible relations with all interested organizations working on methods of analysis and sampling.
(b) The Codex Committee on Methods of Analysis and Sampling should organize its work in such a manner as to keep under constant review all methods of analysis and sampling published in the Codex Alimentarius.
(c) In the Codex methods of analysis, provision should be made for variations in reagent concentrations and specifications from country to country.
(d) Codex methods of analysis which have been derived from scientific journals, theses, or publications, either not readily available or available in languages other than the official languages of FAO and WHO, or which for other reasons should be printed in the Codex Alimentarius in extenso, should follow the standard layout for methods of analysis as adopted by the Codex Committee on Methods of Analysis and Sampling.
(e) Methods of analysis which have already been printed as official methods of analysis in other available publications and which are adopted as Codex methods need only be quoted by reference in the Codex Alimentarius.