BS ISO 21187 pdf download – Milk —Quantitativedetermination ofbacteriological quality — Guidance forestablishing and verifying aconversion relationship between routine method results and anchor method results.
anchor method
reference method
method of analysis Internahonally recognized by experts or by agreement between parties, and used, for instance, in legislation when expressing official limits for bacteriological quality
NOTE It is stressed that, m quaritative microbiology, any obtained vMe is only defined by the method description applied. This appees to any rouilne method as wee as, for instance, to the standard plate coLwbl for the enumeration of microorganisms. For the purpose of conversion, the temi andor method is preferred over the term reference method and therefore is used throughout this International Standard,
3.3
analyte
component or property which is measured by the method of analysis
NOTE The analyte may be the microorganism, stained particles (e.g. microscopic count). components of microorganisms (eg Ilpcpofysaochandes), the result of thel ability to multiply (e.g colony4orming units) or their metabolic activity (e.g. chenge In coictrv*yirredance).
3.4
organIzing laboratory
laboratory. possd,ly appointed by the competent authonties, having the qualified staff and skills to organize, to coordinate arid to report on the outcome of the activities for the establishment or the maintenance of a conversion relationship
4 Principles
4.1 Prerequisites
For establishing and verifying a conversion relationship between the results of a routine method and the anchor method, the following prerequisites apply.
a) The routine method should have been validated acccschng to ISO 161401 1 Procedures for sampling, test sample preservation, sample transport, sample storage, sample pre-treatment, analysas and calculation of results should be documented, strictly standardized and controlled m agreement with ISOIEC 17025, EA41 0. or comparable standards.
b) The anchor method should have been validated. doaimented. strictly standardized and controlled In agreement with ISOi1EC 17025, EA4i10 or comparable standards.
C) The protocol for the establishment of the conversion relationship and its verification should be docurriented. it should follow the guidelines of this International Standard. Approval by competent authorities should be sought where the final aim Is that results from a routine method are to be judged against official limits stated in the anchor method units.
42 Organizational set-up
The establishment and verification of a conversion relationship is based on the examination of test samples with both methods. covering the field of application and the spectrum of the samples as analysed using the routine method.
a) in the bacterial composition, level and properties of the sample population,
b) in the geographical region.
C) over the year, and
d) over different laboratnfles[mstniments. when applying the routine method for situations b) and C) in 4.2.
5.2.2 Range of samples
The levels should, within the measuring range, uniformly cover the range of Interest for the routine method concerned.
Where data are to be transformed before statistical treatment (see 5.5), the data pairs should uniiormty cover the transformed scale.
5.2.3 RepresentatIve samples
It isof the highest priority to work with natural test samples. The test samples should be twly representative Of the ckfferent levels in the population under consideration (see 5.1).
Test samples of raw milk may. In particular, be susceptible to changes between the time of taking the sample and the time of analysis, if sample quality is already poor at sampling This involves a higher risk of ambient influences duflng transport, mixing and storage of test samples. Proper precautions should be taken to avoid this.
With some routine methods, results are almost instantly available. When both the routine and the anchor method are carried out in the same Laboratory, an efficient selection of samples can be based on me outcome of measurements with the routine method, If this is not the case, it is necessary to select a surplus of samples for analysis with both the routine method and the anchor method to follow the guidance given in 5.2.1 and 5.2.2 Another reason for needing a surplus is that some data pairs are likely to become Invalidated (see 5.5.1).
The normal procede for testing with the routine method should be lollowed. This implies that the conditions for sampling, test sample storage, and its transport during the whole procedure should also closely mimic the conditions under which the conversion equation is to be applied.
BS ISO 21187 pdf download – Milk —Quantitative determination ofbacteriological quality — Guidance forestablishing and verifying aconversion relationship between routine method results and anchor method results
