SANS 886-2009 Water quality - Enumeration of micro-organisms in water samples - Guidance on the estimation of variation of results with particular reference to the contribution of .pdf

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1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA

2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any

3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ISBN 978-0-626-22710-4 SANS 886:2009 Edition 1SOUTH AFRICAN NATIONAL STANDARD Water quality Enumeration of micro- organisms in water samples Guidance on

4、the estimation of variation of results with particular reference to the contribution of uncertainty of measurement This national standard is the identical implementation of BS 8496:2007 and is adopted with the permission of British Standards Publishing Ltd. Published by SABS Standards Division 1 Dr

5、Lategan Road Groenkloof Private Bag X191 Pretoria 0001 Tel: +27 12 428 7911 Fax: +27 12 344 1568 www.sabs.co.za SABS This standard may only be used and printed by approved subscription and freemailing clients of the SABS. SANS 886:2009 Edition 1 Table of changes Change No. Date Scope National forewo

6、rd This South African standard was approved by National Committee SABS SC 147B, Water Biological treatment and assessment of water, in accordance with procedures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement. This SANS document was published in March 2009. This

7、standard may only be used and printed by approved subscription and freemailing clients of the SABS.BS 8496:2007 Water quality Enumeration of micro-organisms in water samples Guidance on the estimation of variation of results with particular reference to the contribution of uncertainty of measurement

8、 ICS 03.120.30; 07.100.20 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BRITISH STANDARD SANS 886:2009This standard may only be used and printed by approved subscription and freemailing clients of the SABS.Publishing and copyright information The BSI copyright notice display

9、ed in this document indicates when the document was last issued. BSI 2007 ISBN 978 0 580 49930 2 The following BSI references relate to the work on this standard: Committee reference EH/3/4 Publication history First published January 2007 Amendments issued since publication Amd. no. Date Text affect

10、ed BS 8496:2007 SANS 886:2009This standard may only be used and printed by approved subscription and freemailing clients of the SABS. BSI 2007 i BS 8496:2007 Contents Foreword ii Introduction 1 1 Scope 1 2 Normative references 1 3 Terms and definitions 1 4 General 3 5 Procedure 8 Annexes Annex A (in

11、formative) Worked examples 14 Bibliography 18 List of figures Figure 1 Illustration of hypothetical water sample containing 30 micro-organisms distributed at random throughout 10 equal sized sub-samples 7 List of tables Table A.1 Counts on 10 replicate sub-samples from a sample from each of 5 water

12、sources 14 Table A.2 Replicate counts on daily duplicate sub-samples 16 Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 19 and a back cover. SANS 886:2009This standard may only be used and printed by approved subscription and freemailing clie

13、nts of the SABS.BS 8496:2007 ii BSI 2007 Foreword Publishing information This British Standard was published by BSI and came into effect on 31 January 2007. It was prepared by Subcommittee EH/3/4, Microbiological methods, under the authority of Technical Committee EH/3, Water quality. A list of orga

14、nizations represented on this committee can be obtained on request to its secretary. Supersession This British Standard supersedes DD 260:2003, which is withdrawn. Relationship with other publications This British Standard gives guidance on the interpretation of the requirements in BS EN ISO/IEC 170

15、25:2005 for estimating uncertainty of measurement, in the context of microbial counts in water samples. It is intended to form an adjunct to BS ISO 8199 which gives guidance on the enumeration of micro-organisms in water samples. Use of this document As a guide, this British Standard takes the form

16、of guidance and recommendations. It should not be quoted as if it were a specification and particular care should be taken to ensure that claims of compliance are not misleading. Any user claiming compliance with this British Standard is expected to be able to justify any course of action that devia

17、tes from its recommendations. Presentational conventions The provisions in this standard are presented in roman (i.e. upright) type. Its recommendations are expressed in sentences in which the principal auxiliary verb is “should”. Commentary, explanation and general informative material is presented

18、 in smaller italic type, and does not constitute a normative element. Contractual and legal considerations This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immu

19、nity from legal obligations. SANS 886:2009This standard may only be used and printed by approved subscription and freemailing clients of the SABS. BSI 2007 1 BS 8496:2007 Introduction BS EN ISO/IEC 17025:2005, 5.4.6.2 specifies that “Testing laboratories shall have and shall apply procedures for est

20、imating uncertainty of measurement”. This is difficult to apply to water microbiology because the distribution and behaviour of microbial cells in water is not uniform. The purpose of the present document is to provide practical guidance on how to interpret and implement these requirements within th

21、e context of a water microbiology laboratory. It is intended to form an adjunct to BS ISO 8199:2005. 1 Scope This British Standard gives guidance on interpretation of the requirements specified in BS EN ISO/IEC 17025:2005 with regard to the uncertainty of measurement in microbial counts in water sam

22、ples. It gives guidance on the estimation of variation in results between replicate sub-samples, which will include that due to uncertainty of measurement, in order to assess whether the variation due to uncertainty of measurement has been controlled in accordance with the requirements specified in

23、BS EN ISO/IEC 17025:2005. It is applicable to examination of sub-samples as part of a quality assurance system. It is applicable to samples of all types of water. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references on

24、ly the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. BS EN ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories DD ENV ISO/TR 13843:2001, Water quality Guidance on valida

25、tion of microbiological methods 3 Terms and definitions For the purposes of this British Standard, the following terms and definitions apply. 3.1 accuracy sum of trueness plus precision NOTE This equates to the degree of conformity between the result of a measurement and the true value of the measur

26、and. 3.2 bias systematic errors associated with the methods used NOTE These errors include those due to dilution, population selection, and calibration. SANS 886:2009This standard may only be used and printed by approved subscription and freemailing clients of the SABS.BS 8496:2007 2 BSI 2007 3.3 pr

27、ecision closeness of agreement between independent test results obtained under stipulated conditions NOTE Precision does not relate to the true value or the specified value. It is usually expressed in terms of imprecision and computed as a standard deviation of the test results. DD ENV ISO/TR 13843:

28、2001, 2.25 3.4 imprecision random errors incurred in applying the methods together with random variation in the test material 3.5 limit of detection lowest number of micro-organisms that need to be present in the test portion of water examined for their presence to be detected by a particular microb

29、iological test NOTE Limit of detection should not be confused with limit of determination which is the lowest average number of micro-organisms in a body of water that would result in a 95% probability of giving a positive result when a representative test portion is examined by a particular microbi

30、ological test. 3.6 measurand specific quantity that is subjected to measurement 3.7 repeatability closeness of the agreement between the results of successive measurements of the same measurand carried out under the same conditions of measurement within a short period of time NOTE 1 Modified from In

31、ternational vocabulary of basic and general terms in metrology, 1993 1. NOTE 2 Conditions of measurement include, the method of analysis; the analyst; the measurement instrument and the conditions under which it is used; and the location. NOTE 3 Within a short period of time is normally considered t

32、o be within one hour. 3.8 reproducibility closeness of the agreement between the results of measurements of the same measurand carried out under different conditions of measurement NOTE 1 Modified from International vocabulary of basic and general terms in metrology, 1993 1. NOTE 2 Conditions of mea

33、surement include, the method of analysis; the analyst; the measurement instrument and the conditions under which it is used; the location; and the time. 3.9 reference culture culture of a micro-organism obtained from a recognized national culture collection 3.10 reference material material containin

34、g a defined population of micro-organisms from one or more reference cultures in numbers expected to fall within a defined range for use in the assessment of a measurement method SANS 886:2009This standard may only be used and printed by approved subscription and freemailing clients of the SABS. BSI

35、 2007 3 BS 8496:2007 3.11 certified reference material reference material accompanied by a certificate stating the expected microbial count with an associated confidence interval 3.12 uncertainty of measurement UM parameter associated with the result of a measurement, that characterizes the dispersi

36、on of the values that can reasonably be attributed to the measurand Guide to the expression of uncertainty in measurement, 1995 2 3.13 validation process providing evidence that a method is capable of serving its intended purpose in detecting or quantifying a specific microbe or microbial group with

37、 the required level of precision and accuracy NOTE Modified from DD ENV ISO/TR 13843:2001, 4.2.1. 3.14 secondary validation process providing evidence that a method validated elsewhere performs within the users laboratory according to the specifications determined in the original validation NOTE 1 A

38、lso known as verification. NOTE 2 Modified from DD ENV ISO/TR 13843:2001, 2.38 and 4.2.3. 3.15 sample volume of water collected from the body of water under investigation 3.16 sub-sample volume of water taken from a sample 3.17 test portion volume of water examined in a particular test NOTE The test

39、 portion may comprise the whole sample or a sub-sample. 4 General 4.1 Significance of requirements specified in BS EN ISO/IEC 17025 BS EN ISO/IEC 17025:2005, 5.4.6.2 specifies: “Testing laboratories shall have and shall apply procedures for estimating uncertainty of measurement. In certain cases the

40、 nature of the test method may preclude rigorous, metrologically and statistically valid, calculation of uncertainty of measurement. In these cases the laboratory shall at least attempt to identify all the components of uncertainty and make a reasonable estimation, and shall ensure that the form of

41、reporting of the result does not give a wrong impression of the uncertainty. Reasonable estimation shall be based on knowledge of the performance of the method and on the measurement scope and shall make use of, for example, previous experience and validation data.” SANS 886:2009This standard may on

42、ly be used and printed by approved subscription and freemailing clients of the SABS.BS 8496:2007 4 BSI 2007 The document EA-04/10 Accreditation for microbiological laboratories 3, produced by the joint EA/EURACHEM Working Group, supplements BS EN ISO/IEC 17025 and states the following in paragraphs

43、5.2 to 5.4. NOTE Points of particular importance to the present British Standard are indicated in bold type. “5.2 Microbiological tests generally come into the category of those precluding rigorous, metrologically and statistically valid calculation of uncertainty of measurement. It is generally app

44、ropriate to base the estimation of uncertainty on repeatability and reproducibility data alone, but ideally including bias (e.g. from proficiency testing results). The individual components of uncertainty should be identified and demonstrated to be under control and their contribution to the variabi

45、lity of results evaluated. Some components (e.g. pipetting, weighing and dilution effects) may be readily measured and easily evaluated to demonstrate a negligible contribution to overall uncertainty. Other components (e.g. sample stability and sample preparation) cannot be measured directly and the

46、ir contribution cannot be evaluated in a statistical manner but their importance to the variability of results should be considered also. 5.3 It is expected that accredited microbiological testing laboratories will have an understanding of the distributions of organisms within the matrices they test

47、 and take this into account when sub-sampling. However, it is not recommended that this component of uncertainty is included in estimates unless the clients needs dictate otherwise. The principal reasons for this are that uncertainty due to distribution of organisms within the product matrix is not

48、a function of the laboratorys performance and may be unique to individual samples tested and because test methods should specify the sample size to be used taking into account poor homogeneity. 5.4 The concept of uncertainty cannot be applied directly to qualitative test results such as those from d

49、etection tests or the determination of attributes for identification. Nevertheless, individual sources of variability, e.g. consistency of reagent performance and analyst interpretation, should be identified and demonstrated to be under control. Additionally, for tests where the limit of detection is an important indication of suitability, the uncertainty associated with the inocula used to determine the limit should be estimated and its significance evaluated. Laboratories should also be aware of the incidence of false positive and