1、Designation: E2764 11Standard Practice forUncertainty Assessment in the Context of Seized-DrugAnalysis1This standard is issued under the fixed designation E2764; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides guidance on the concept ofuncertainty and its application to the qualitative and quantita-tive analysis
3、of seized drugs. In this context, uncertaintyencompasses limitations of qualitative methods as well asnumerical ranges as applied to quantitative analyses.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard doe
4、s not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Stan
5、dards:2E2329 Practice for Identification of Seized DrugsE2327 Practice for Quality Assurance of Laboratories Per-forming Seized-Drug AnalysisE2549 Practice for Validation of Seized-Drug AnalyticalMethods2.2 ISO Standards:3ISO 3534-1:1993 StatisticsPart 1: Probability and Gen-eral Statistical Terms3.
6、 Significance and Use3.1 Application of UncertaintyQualitative and quantita-tive analyses require different approaches, refer to the refer-ences for additional information. Analysts shall understand thelimitations of qualitative and quantitative determinations andhave tools to estimate a value for m
7、easurement uncertainty ofrelevant, but not necessarily all, numerical results. In thisregard, efforts should be made to use the vocabulary, symbols,and formatting expressed in documents published by interna-tional standardizing organizations such as ISO and ASTMInternational.3.1.1 An understanding o
8、f uncertainty is fundamental to theinterpretation and reporting of results.3.1.2 The term “uncertainty” does not imply doubt; rather,its consideration provides assurance that results and conclu-sions from methods and analytical schemes are fit for purpose.3.1.3 The concept of uncertainty shall be co
9、nsidered forboth qualitative and quantitative results.3.1.4 Laboratory management shall ensure that uncertaintybe addressed through the provision of training, procedures anddocumentation.3.1.5 Laboratory management should consider customerrequirements, such as a request for qualitative versus quanti
10、-tative determinations, which influence the assessment of un-certainty.3.2 The benefits of understanding and determining uncer-tainty in this context include:3.2.1 Enhancing confidence through increased understand-ing of results,3.2.2 Providing a mechanism to express the reliability ofresults,3.2.3
11、Enabling the laboratory management and customer toevaluate the fitness for purpose of results,3.2.4 Facilitating the identification of procedural limitationsand providing a basis for improvement, and3.2.5 Complying with accreditation requirements.4. Qualitative Analysis4.1 The identification of seiz
12、ed drugs requires the combina-tion of methods to form an analytical scheme (see PracticeE2329).4.2 Individual methods have limitations and, consequently,uncertainty. Uncertainty of qualitative methods is not typicallyamenable to being expressed in numerical terms.4.3 Understanding these limitations
13、enables laboratory per-sonnel to build an appropriate analytical scheme to correctlyidentify a drug or other chemical.1This practice is under the jurisdiction of ASTM Committee E30 on ForensicSciences and is the direct responsibility of Subcommittee E30.01 on Criminalistics.Current edition approved
14、June 1, 2011. Published June 2011. DOI: 10.1520/E2764-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Ava
15、ilable from International Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http:/www.iso.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.3.1 It is expected that in the abse
16、nce of unforeseen error,an appropriate analytical scheme effectively results in nouncertainty in reported identifications.4.3.2 Relevant limitations of an analytical scheme (forexample, inability to differentiate isomers, unavailability ofreference standard, limits of detection and resolution) shoul
17、dbe documented and might need to be included in the report (seereporting examples in 7.2).5. Quantitative Measurements5.1 Quantitative measurements have an associated uncer-tainty, which is defined as “an estimate attached to a test resultwhich characterizes the range of values within which the true
18、value is asserted to lie” (ISO 3534-1:1993).5.2 A precise calculation of measurement uncertainty maynot always be required.5.2.1 Laboratory personnel shall understand the contribut-ing factors of measurement uncertainty for each analyticalprocedure and evaluate them with respect to customer, accredi
19、-tation, and jurisdictional requirements.5.2.2 Where a value is critical, such as a weight or puritylevel close to a statutory threshold, an appropriate measure-ment uncertainty determination shall be applied.5.3 Primary numerical values reported in the analysis ofseized drugs are weight and purity.
20、 Where other values aremeasured (for example, size, volume, estimated tablet num-bers), the same principles stated herein apply.6. Estimation of Measurement Uncertainty forQuantitative Determinations6.1 Sources of Uncertainty for Weight DeterminationsTheuncertainty of a reported value is dependant o
21、n the weighingprocess. Factors for consideration include:6.1.1 Single versus multiple items (number of weighingoperations),6.1.2 Tare function as a separate weighing operation,6.1.3 Extrapolation of population weight from limited sam-pling of multiple items,6.1.4 Aggregate weighings,6.1.5 Incomplete
22、 recovery of material from the packaging,6.1.6 Balance selection (for example, readability, capacity),and6.1.7 Balance operation (for example, sample placement onpan, environmental conditions).6.2 Sources of Uncertainty for Purity DeterminationTheuncertainty of a reported purity value is dependant u
23、pon theentire quantitation process. Factors for consideration include:6.2.1 Sampling Plan (for example, handling of multipleexhibits):6.2.1.1 Sample homogeneity.6.2.2 Analytical Method:6.2.2.1 Sample preparation (for example, sample size, ma-trix effects, solubility),6.2.2.2 Analytical technique,6.2
24、.2.3 Reference material (for example, purity of standard),6.2.2.4 Equipment and instrument properties (for example,glassware, pipetters, balances, chromatographs),6.2.2.5 Concentration of analyte, and6.2.2.6 Environmental conditions.6.3 Factors Relevant to Estimation of Measurement Uncer-tainty:6.3.
25、1 When estimating measurement uncertainty, considerthe following sources of error:6.3.1.1 Analytical ErrorSystematic and random errorboth contribute to measurement uncertainty and shall beaddressed through method validation and quality assurancepractices (see Practices E2327 and E2549). Systematic e
26、rrorshould be characterized and minimized for all validated pro-cedures.6.3.1.2 Sampling ErrorThe sample and sampling proce-dure are often the greatest contributors to measurement uncer-tainty.6.3.2 Where appropriate, confidence levels (for example,95 % or 99.7 %) shall be determined based on consid
27、erationsrelevant to the analytical context.6.3.3 Record uncertainty information in validation docu-ments, case records, or both.6.4 Approaches for Estimating Measurement Uncertainty:6.4.1 Uncertainty Budget Approach:6.4.1.1 In this approach all sources of error are separatelyidentified and tabulated
28、.6.4.1.2 A value is assigned to each source of error (collec-tively or individually) using either: empirical data (for ex-ample, from validation process, historical performance data,control chart data, proficiency tests); published data (forexample, volumetric glassware tolerances); or combination o
29、fempirical and published data.6.4.1.3 Where a source has an uncertainty which is insig-nificant compared to other sources, it can be excluded. Docu-ment the reasons for any exclusions.6.4.1.4 The remaining significant values are used to calcu-late the combined standard uncertainty and expanded uncer
30、-tainty.6.4.2 Non-Budget Approaches:6.4.2.1 The sources of uncertainty that are separately as-sessed in the budget method are collectively assessed byexperimental measurement. In this approach data obtainedfrom a statistically significant number of replicate analysesutilizing a validated method with
31、 an appropriate sampling planmay be utilized to calculate the standard or expanded uncer-tainty.6.4.2.2 An alternate approach involves the use of twostandard deviations (2s) of the test method results fromreproducibility data from the validation studies. This providesan approximation of the measurem
32、ent uncertainty for non-critical values.7. Reporting of Uncertainty7.1 ReportingUncertainty should be reported when ap-propriate. Factors which influence the decision to reportuncertainty include:7.1.1 Jurisdictional:7.1.1.1 Prevailing statutory requirement,7.1.1.2 Relevant governing body (agency) r
33、equirements,7.1.1.3 Customer requests, and7.1.1.4 Potential exculpatory value.E2764 1127.1.2 Types of Analysis:7.1.2.1 QualitativeQualitative results where limitations ofanalytical scheme are known and relevant (for example,inability to differentiate isomers, unavailability of a referencestandard),
34、and7.1.2.2 QuantitativeQuantitative measurements where avalue is critical (for example, weight or purity level close to astatutory threshold).7.1.3 Laboratory Accreditation Requirements.7.2 Reporting Examples of UncertaintyReporting require-ments and styles differ among agencies and jurisdictions. T
35、heexamples listed below are drawn from laboratories with variedrequirements. The expression of uncertainty is in italics andbold.7.2.1 Qualitative Results:7.2.1.1 Contains ephedrine or pseudoephedrine. Item tested:5.2 g net.7.2.1.2 Contains cocaine (salt form not determined).7.2.2 Quantitative Resul
36、tsFactors to be considered whenreporting measurement uncertainty include use of significantfigures, confidence intervals and rounding/truncating of results.7.2.2.1 Active drug ingredient (established or commonname) methamphetamine hydrochloride:Gross weight: 25.6 gNet weight: 5.2 gConcentration or p
37、urity: 54.7 % (62.8 %)AAmount of actual drug: 2.8 gReserve weight: 5.1 gAThis value represents the quantitative uncertainty measurement estimate forthe laboratory system.7.2.2.2 Positive for cocaine in the sample tested:Net weight of total sample: 5.23 g 6 0.03 gQuantitation: 54.7 % 6 2.8 %7.2.2.3 S
38、ample tested positive for cocaine:Net weight: 5.23 gPurity: 54.7 %Confidence range: 62.8 %ACalculated net weight of drug: 2.8 g of cocaineAConfidence range refers to a 95 % confidence level.7.2.2.4 Cocaine was identified in the Item 1 powder at apurity of 65 6 9 % (99.7 % confidence level). The Item
39、 1powder weighed 800 mg 6 4 mg (99.7 % confidence level).7.2.2.5 White Powder: 5.6 gThe range of heroin concen-tration identified in the sample was not less than 53.2 % andnot more than 56.2 %.8. Training8.1 Individuals responsible for determining, evaluating anddocumenting uncertainty in the contex
40、t of seized-drug analysisshall be capable of competently demonstrating familiarity withfoundational concepts and principles of estimating uncertainty.Useful topics to review include:8.1.1 General metrology to include: terminology, symbols,formulae, publications, international organizations, and glob
41、alapplication as related to seized-drug analysis;8.1.2 The concepts of random and systematic error, accu-racy, precision (repeatability, reproducibility, and their condi-tions), statistical control, standard and expanded uncertainty,and propagation of error;8.1.3 Reporting conventions including use
42、of significantfigures, truncation, and rounding; and8.1.4 Basic statistics (descriptive and inferential) to include:measures of central tendency (for example, median), measuresof variation, statistical modeling, sampling, probability, confi-dence interval, and significance level.8.2 All analysts sha
43、ll be capable of explaining their labora-torys procedures for evaluating uncertainty of qualitative andquantitative analyses.9. Keywords9.1 analytical error; confidence level; measurement uncer-tainty; method validation; quantitative measurements; sam-pling error; seized drugs; sources of uncertaint
44、y; uncertainty;uncertainty budgetREFERENCES(1) E29 04: Standard Practice of Using Significant Digits in Test Data toDetermine Conformance with Specifications, West Conshohosken, PA.(2) The International Vocabulary of Basic and General Terms in Metrol-ogy, International Organization for Standardizati
45、on, Switzerland,2008.(3) ISO 3534-1: Statistics Vocabulary and Symbols, Part 1: Probabilityand General Statistical Terms; ISO 3534-2: Statistics Vocabularyand Symbols, Part 2: Statistical Quality Control; International Orga-nization for Standardization, Switzerland, 2006.(4) ISO 5725-1: Accuracy (Tr
46、ueness and Precision) of MeasurementMethods and Results Part 1: General Principles and Definitions,International Organization for Standardization, Switzerland, 1994.(5) ISO/IEC 17025: General Requirements for the Competence of Testingand Calibration Laboratories, International Organization for Stand
47、ard-ization, 2005.(6) Guide to the Expression of Uncertainty in Measurement, ISBN 92-67-10188-9, International Organization for Standardization, Switzer-land, 2008.(7) Guidelines for Evaluation and Expressing the Uncertainty of NISTMeasurement Results, National Institute of Standards and Technology,
48、NIST Technical Note 1297, 1994 Edition.(8) Kimothi, S.K., The Uncertainty of Measurements Physical andChemical Metrology Impact and Analysis, Milwaukee AmericanSociety for Quality, 2002.(9) Measurement Uncertainty Arising from Sampling: A Guide to Meth-ods and Approaches, 1st edition, Eurachem/CITAC
49、 Guide, 2007.(10) Natrella, M., Experimental Statistics, National Bureau of Standards(NBS), 1966.(11) Quantifying Uncertainty in Analytical Measurements, 2nd edition,Eurachem, 2000.(12) Skoog, D.A., et al., Fundamentals of Analytical Chemistry, 8thEdition, Brooks Cole, 2003.E2764 113(13) Taylor, B.N., Guide for the Use of the International System of Units(SI), National Institute of Standards and Technology, April 1995.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. U
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