1、 Reference number ISO/TS 20612:2007(E) ISO 2007TECHNICAL SPECIFICATION ISO/TS 20612 First edition 2007-12-01 Water quality Interlaboratory comparisons for proficiency testing of analytical chemistry laboratories Qualit de leau Comparaisons interlaboratoires pour des essais de comptence de laboratoir
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6、riting from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2007 All rights reservedISO/TS
7、20612:2007(E) ISO 2007 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope 1 2 Normative references 1 3 Terms and definitions .2 4 Symbols 2 5 Requirements relating to proficiency test provider .4 6 Participants 4 7 Proficiency test design .4 8 Execution of proficiency tests6 9
8、Proficiency test evaluation .8 10 Presentation of results15 11 Archiving and managing the results15 Annex A (informative) Example of Q-method estimation principle16 Annex B (informative) Determination of repeatability standard deviation, s r .18 Annex C (informative) Example of evaluation method in
9、Clause 919 Annex D (informative) Example of variance function calculation (9.3)21 Bibliography 25 ISO/TS 20612:2007(E) iv ISO 2007 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work
10、 of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmen
11、tal, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The ma
12、in task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. In
13、 other circumstances, particularly when there is an urgent market requirement for such documents, a technical committee may decide to publish other types of normative document: In other circumstances, particularly when there is an urgent market requirement for such documents, a technical committee m
14、ay decide to publish other types of document: an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in an ISO working group and is accepted for publication if it is approved by more than 50 % of the members of the parent committee casting a vote; an ISO
15、Technical Specification (ISO/TS) represents an agreement between the members of a technical committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting a vote. An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be conf
16、irmed for a further three years, revised to become an International Standard, or withdrawn. If the ISO/PAS or ISO/TS is confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an International Standard or be withdrawn. Attention is drawn to the p
17、ossibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO/TS 20612 was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 2, Physical, chemical and biochemica
18、l methods. ISO/TS 20612:2007(E) ISO 2007 All rights reserved v Introduction Participation in interlaboratory tests in various test fields offers a testing laboratory an opportunity to obtain an objective picture of its proficiency. Such tests serve as a confidence-building measure both for the labor
19、atory itself and for prospective clients. This Technical Specification is based on the following international recognized documents: ISO/IEC Guides 43-1 and 43-2; ISO 13528; The International Harmonized Protocol for the Proficiency Testing of Analytical Chemistry Laboratories (IUPAC, ISO, AOAC); ILA
20、C Guide 13; ISO/IEC 17025; ISO 5725-1 and ISO 5725-2. As these documents only define a framework for design, execution and evaluation of proficiency testing by interlaboratory comparisons, this Technical Specification describes in detail an evaluation procedure which is especially suitable for the s
21、ector of water, waste water and sludge analysis, where results of interlaboratory comparisons play an important role in the admission of laboratories to certain analytical tasks. Therefore, the fairness of assessment of laboratories must be guaranteed. Assessment should not be dependent on the provi
22、der, the date, or the method of evaluation. TECHNICAL SPECIFICATION ISO/TS 20612:2007(E) ISO 2007 All rights reserved 1 Water quality Interlaboratory comparisons for proficiency testing of analytical chemistry laboratories 1 Scope This Technical Specification specifies the criteria related to profic
23、iency testing by interlaboratory comparisons in the field of water, waste water and sludge analysis. In particular, it specifies the requirements in respect to proficiency test providers and to the design, execution and evaluation of laboratory proficiency comparisons. This document may be used if t
24、he determinands in the interlaboratory test may be regarded as capable of measurement with a certain degree of continuity. This is generally the case for chemical constituents and physicochemical determinands, but continuity does not always exist in the case of biological and/or microbiological dete
25、rminands. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3534-1, Stat
26、istics Vocabulary and symbols Part 1: General statistical terms and terms used in probability ISO 5725-1, Accuracy (trueness and precision) of measurement methods and results Part 1: General principles and definitions ISO 5725-1:1994/Cor.1:1998, Accuracy (trueness and precision) of measurement metho
27、ds and results Part 1: General principles and definitions Technical Corrigendum 1 ISO 5725-2, Accuracy (trueness and precision) of measurement methods and results Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method ISO 13528, Statistical m
28、ethods for use in proficiency testing by interlaboratory comparisons ISO/IEC Guide 43-1, Proficiency testing by interlaboratory comparisons Part 1: Development and operation of proficiency testing schemes ISO/IEC Guide 43-2, Proficiency testing by interlaboratory comparisons Part 2: Selection and us
29、e of proficiency testing schemes by laboratory accreditation bodies ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories ISO/IEC 17020, General criteria for the operation of various types of bodies performing inspection ISO/TS 20612:2007(E) 2 ISO 2007 All ri
30、ghts reserved3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 3534-1, ISO 5725-1, ISO 5725-2, ISO/IEC Guide 43-1, ISO/IEC Guide 43-2 and the following apply. 3.1 breakdown point smallest percentage of outlier laboratories above which the estimation me
31、thod may be entirely inapplicable 3.2 efficiency ratio of the variance of the optimum estimation method for normal distribution to the variance of the estimation method under consideration, each assuming a normal distribution NOTE This is expressed as a percentage. 3.3 sample totality of a homogeneo
32、us analysis material with an identical composition or quality (similar to term batch) 3.4 subsample defined portion of a sample obtained by suitable sample division and identical in terms of composition 4 Symbols d iAbsolute difference between log-linear variance function and the logarithm of the re
33、producibility standard deviation G 1 (x i ) Generalized distribution function of interlaboratory differences with continuity correction (s R ) G 2 (x i ) Generalized distribution function of intralaboratory differences with continuity correction (s r ) g Quality limit H 1 (x i ) Generalized distribu
34、tion function of interlaboratory differences (s R ) H 2 (x i ) Generalized distribution function of intralaboratory differences (s r ) i Index denoting the serial number of one of p samples J iNumber of participants in the case of sample i j Index denoting the serial number of one of J participating
35、 laboratories k 1 ,k 2Correction factors for calculating z U -score Overall mean iOverall mean of i-th sample x aAssigned value n jNumber of measurements made by laboratory j ISO/TS 20612:2007(E) ISO 2007 All rights reserved 3 q Quantile parameter p Number of samples (levels) PG 0 ,PG 1Testing value
36、s for testing variance function s RReproducibility standard deviation i R s Reproducibility standard deviation of i-th sample i R s Reproducibility standard deviation for sample i adjusted using a variance function s rRepeatability standard deviation Standard deviation for proficiency assessment W W
37、eighting matrix X Design matrix X TTransposed design matrix x iDiscontinuity point y Arithmetic mean of test results of an unspecified laboratory y jiMeasurement result for the i-th measurement made by laboratory j y jArithmetic mean of measurement results of laboratory j z z-Score, i.e. standardize
38、d deviation of laboratory result from assigned value z UCorrected z-score Function for determining the Hampel estimator 2 p 2;0,9595 % chi-squared quantile for p 2 degrees of freedom Distribution function of standard normal distribution Significance level Relative reproducibility standard deviation
39、Vector of logarithms of standard deviations 0 , 1Parameters of log-linear variance function 0 Estimate of logarithm of relative reproducibility standard deviation if independent from concentration level ISO/TS 20612:2007(E) 4 ISO 2007 All rights reserved5 Requirements relating to proficiency test pr
40、ovider Proficiency testing by interlaboratory comparisons must lie in the responsibility of specialists who are familiar not only with the requirements relating to the design, execution and evaluation of interlaboratory tests, but also with the analytical methods to be tested, and who have demonstra
41、ted their specialist knowledge. Against this background, it is recommended that the test provider regularly organizes interlaboratory tests in the relevant test field. The proficiency test provider must maintain an adequately documented quality management system based on the criteria specified in IS
42、O/IEC 17020 or ISO/IEC 17025, covering all necessary framework conditions, responsibilities and standard operation procedures. In addition all measurements within the framework of the provided proficiency test should fulfil the technical requirements as specified in ISO/IEC 17025. An advisory group
43、that includes specialists for all the fields involved should be appointed to enable the relevant interlaboratory test system to be brought into line with the state of the art and proper account to be taken of the specialist requirements relating to the interlaboratory tests. Keeping a written record
44、 of the groups decisions is recommended. 6 Participants Only laboratories that have the requisite staffing and equipment for the tests to be performed shall take part in an interlaboratory test. Each participating laboratory should appoint a member of staff to be responsible for maintaining contact
45、with the proficiency test manager and ensuring that the analyses are correctly carried out in accordance with the proficiency test managers instructions. 7 Proficiency test design 7.1 Proficiency test plan All details of the proficiency test design should be laid down in a plan prior to the start of
46、 the interlaboratory test. This includes especially details about: involved staff; sample matrix; determinands to be analysed; concentration level of the determinand; number of samples; sample containers; sample preservation; distribution of samples; communication with participants of the proficienc
47、y test (PT); homogenization method; homogeneity and stability check; ISO/TS 20612:2007(E) ISO 2007 All rights reserved 5 method for stipulating the assigned value; schedule; evaluation and assessment procedure. All relevant practices listed in ISO Guide 43-1 shall be fulfilled. 7.2 Sample selection
48、In selecting the sample material, account shall be taken of the objectives of the interlaboratory test, the target concentration levels, the required homogeneity and stability of the samples, and the transport and storage facilities. In general, real or spiked real samples shall be given preference
49、over synthetic ones. Sample matrix and concentration levels should reflect routine conditions. 7.3 Selection of determinands The determinands selected in a particular case and their number shall be defined precisely in accordance with the target group of participants or with the reason for the interlaboratory test. Determinands shall be defined accurately, i.e. whether a certain form (e.g. soluble) or the total concentration shall be determined
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