ASTM D6956-03

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:D6956–03
Standard Guide for
Demonstrating and Assessing Whether a Chemical
Analytical Measurement System Provides Analytical Results
Consistent with Their Intended Use
This standard is issued under the fixed designation D6956; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope and Quality Control Planning and Implementation
D5792 Practice for Generation of Environmental Data Re-
1.1 This guide describes an approach for demonstrating the
lated to Waste Management Activities: Development of
quality of analytical chemical measurement results from the
Data Quality Objectives
application of a measurement system (that is, method or
D5956 Guide for Sampling Strategies for Heterogeneous
sequenceofmethods)totheanalysisofenvironmentalsamples
Wastes
ofsoil,water,air,orwaste.Thepurposeofsuchmeasurements
D6044 GuideforRepresentativeSamplingforManagement
can include demonstrating compliance with a regulatory limit,
of Waste and Contaminated Media
determining whether a site is contaminated above some speci-
D6233 Guide for Data Assessment for Environmental
fied level, or determining treatment process efficacy.
Waste Management Activities
1.2 This guide describes a procedure that can be used to
D6250 Practice for Derivation of Decision Point and Con-
assess a measurement system used to generate analytical
fidenceLimitforStatisticalTestingofMeanConcentration
results for a specific purpose. Users and reviewers of the
in Waste Management Decisions
analytical results can determine, with a known level of confi-
D6311 Guide for Generation of Environmental Data Re-
dence, if they meet the quality requirements and are suitable
lated to Waste Management Activities: Selection and
for the intended use.
Optimization of Sampling Design
1.3 This protocol does not address the general components
D6582 Guide for Ranked Set Sampling: Efficient Estima-
of laboratory quality systems necessary to ensure the overall
tion of a Mean Concentration in Environmental Sampling
quality of laboratory operations. For such systems, the user is
D6597 PracticeforAssessmentofAttainingCleanUpLevel
referred to International Standards Organization (ISO) Stan-
for Site Closure
dard17025ortheNationalEnvironmentalLaboratoryAccredi-
2.2 Other Documents:
tation Conference (NELAC) laboratory accreditation stan-
Guidelines for Evaluating and Expressing Uncertainty of
dards.
NIST Measurement Results, National Institute of Standard
1.4 This standard does not purport to address all of the
Technology Technical Note 1297, 1994
safety concerns, if any, associated with its use. It is the
ISO/IEC 17025:1999 General Requirements for the Com-
responsibility of the user of this standard to establish appro-
petence of Testing and Calibration Laboratories
priate safety and health practices and determine the applica-
Quantifying Uncertainty in Analytical Measurement,
bility of regulatory requirements prior to use.
EURACHEM/ CITAC Guide, second edition, 2000
2. Referenced Documents
3. Terminology
2.1 ASTM Standards:
3.1 Definitions:
D4687 Guide for General Planning of Waste Sampling
3.1.1 action level (AL)—the level above or below which
D5283 Practice for Generation of Environmental Data Re-
will lead to the adoption of one of two alternative actions.
lated to Waste Management Activities: Quality Assurance
3.1.2 analyte—the constituent to be measured.
3.1.3 bias—the difference between the value determined
usingthemeasurementprotocolinquestionandthetruevalue;
This guide is under the jurisdiction of ASTM Committee D34 on Waste
Management and is the direct responsibility of Subcommittee D34.01.01 on
operationally the difference between the expected mean of the
Planning for Sampling.
Current edition approved Nov. 18, 2003. Published December 2003. DOI:
10.1520/D6956-03.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available from National Institute of Standards and Technology (NIST), 100
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Standards volume information, refer to the standard’s Document Summary page on Available from theAmerican National Standards Institute (ANSI), 25 W. 43rd
the ASTM website. St., 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6956–03
sample test results and an accepted true value. D5792 4.3.4 Method of chemical preservation (for example, not
3.1.4 data quality objective (DQO)—qualitative and quan- preserved, chemical used),
titative statements of the overall level of uncertainty that a 4.3.5 Chain-of-custody requirements, if any,
decision-maker is willing to accept in results or decisions 4.3.6 Analytical methods that must be used, if any,
derivedfromenvironmentalmeasurements,includesuncertain-
4.3.7 Measurement quality requirements expressed as
ties in sampling location, sample handling, and sample analy- DQOs or MQOs and action limits,
sis.
4.3.8 Allowable interferences as described in 10.4,
3.1.5 laboratory control sample—an aliquot of the sample
4.3.9 Documentation requirement, and
matrix, free from the analytes of interest, spiked with verified
4.3.10 Subcontracting restrictions/requirements.
known amounts of analytes, or a material containing known
4.4 Users/decision makers should consult with the labora-
and verified amounts of analytes.
tory about these issues during the analytical design stage. This
3.1.6 matrix spike—an aliquot of the sample spiked with
will allow the design of sample collection process and project
known levels of the target analytes.
scheduletoaccommodatethelaboratoryactivitiesnecessaryto
3.1.7 measurement quality objectives (MQOs)—
determine the desired level of measurement quality. The
quantitative statements of the acceptable level of selectivity,
number of samples, budgets, and schedules should also be
sensitivity, bias, and precision for measurements of the analyte
discussed.
of interest in the matrix of concern.
3.1.8 measurement system—all elements of the analytical
5. Limitations and Assumptions
process including laboratory subsampling, sample preparation
5.1 This guide deals only with samples from the time the
and cleanup, and analyte detection and quantitation, including
laboratory receives the samples until the time the analytical
the analysts.
results are provided to the user including necessary documen-
3.1.9 method of standard additions—theadditionofaseries
tation.
of known amounts of the analytes of interest to more than one
5.2 Aspects of environmental measurements that are within
aliquotofthesampleasameansofcorrectingforinterferences.
the control of the laboratory are normally specified by the
3.1.10 reference material (RM)—the generic term referring
project stakeholders in the form of MQOs. MQOs are a subset
to a certified material.
of the data quality objectives (DQOs). The DQOs describe the
3.1.11 selectivity—the ability to accurately measure the
overallmeasurementqualityandtolerableerrorofthedecision
analyte in the presence of other sample matrix components or
for the project while the MQOs describe the uncertainty of the
analytical process contaminants.
analytical process only. The DQO overall level of uncertainty
3.1.12 surrogate —a substance with properties that mimic
includes uncertainty from both sampling and environmental
the performance of the analyte of interest in the measurement
laboratory measurement operations.Additional information on
system, but which is not normally found in the sample of
the DQO process and establishing the level of analytical
concern and is added for quality control purposes.
uncertainty can be found in the references provided in Section
2.
4. Significance and Use
5.3 This guide applies whether the measurements are per-
4.1 This guide is intended for use by both generators and
formed in a fixed location or in the field (on-site).
users of analytical results. It is intended to promote consistent
5.4 This guide assumes that the laboratory is operating with
demonstration and documentation of the quality of the mea-
alladministrativeandanalyticalsystemsfunctioningwithinthe
surement results and facilitate determination of the validity of
quality assurance and quality control protocols and procedures
measurements for their intended use.
described in their quality system documents (quality assurance
4.2 This guide specifies documentation that a laboratory
plan and standard operating procedures).
should supply with the analytical results to establish that the
5.5 Thisguidedoesnotaddressmulti-laboratoryapproaches
resultingmeasurements:(1)meetmeasurementqualityrequire-
to demonstrating acceptable laboratory performance such as
ments; (2) are suitable for their intended use; and (3) are
collaborative testing, inter-laboratory studies, or round-robin
technically defensible.
types of studies.
4.3 Whiletheguidedescribesinformationthatthemeasure-
ment results provider needs to give the user/decision maker, in
6. Outline of Approach
order for measurement providers to supply data users with
appropriate data, information is needed from the data user. 6.1 This guide uses the concepts of bias and precision to
Examples of information that the user should provide to the describe uncertainty in a measurement system. The approach
laboratory,inadditiontotheanalytesofconcern(includingthe set forth in this guide employs two fundamental properties of
form of the analyte that is to be determined, for example, total measurement systems: bias and precision to determine the
lead, dissolved lead, organic lead, inorganic lead), include but quality of the analytical results. The guide singles out selec-
are not limited to: tivity, a component of bias, for special emphasis. Sensitivity is
4.3.1 Type of material (that is, matrix—fresh or salt water, also discussed since, unless a measurement system is sensitive
coal fly ash, sandy loam soil, wastewater treatment sludge), enough to measure the analytes of interest at the level of
4.3.2 Maximum sample holding time, interest, it is not capable of being used for the purpose at hand.
4.3.3 Projected sampling date and delivery date to the Both areas are frequently highlighted for demonstration in
laboratory, acceptable environmental measurement collection efforts.
D6956–03
6.2 This guide provides examples of approaches that deter- decreased. Therefore, showing that a different measurement
mine bias, precision, selectivity, and sensitivity of a measure- technique yields the same results as the subject technique
ment system used to analyze a set of samples. It also provides servestovalidatetheabilityofthesubjectsystemtoyieldvalid
examples of factors laboratories should consider in designing measurements. If the two techniques disagree, there is a
the demonstration.
possibility of systematic or random error in one or both
techniques.
6.3 This guide describes, in general terms, the rigor of the
demonstration of bias, precision, selectivity, and sensitivity
6.6.2 Option 2—The next lower level of certainty is ob-
that should be conducted for a set of samples. It describes the tained by determining the bias, precision, sensitivity, and
appropriate use of public literature and historical laboratory
selectivity of the candidate measurement system using refer-
performance information to minimize the need to collect
ence materials provided by NIST, or some other appropriate
additional experimental measurements.
national certifying authority (for example, Standards Canada,
6.4 When analytical performance results are already avail- DIN). Such reference materials would have been confirmed by
the use of multiple methods, each using a different analytical
able on the measurement system’s response to the type of
sample to be analyzed (for example, historical results from the principle. Comparison of the test results from new methods
with published reference values on such materials can be used
laboratory conducting the demonstration, method developer
information), such information may be used to determine one to determine measurement system bias. Commercially pro-
or more of the measurement properties (that is, bias, precision, ducedreferencematerialsmayalsobeused,butthetruevalues
selectivity, sensitivity). Only very limited amounts of new are usually developed using only one (sometimes two) analyti-
measurements would then be necessary to support the conclu- cal technique(s). The reliable use of reference standards is
sions drawn from the existing information. extremely sensitive to the degree that the reference materials
havethesamematrix/analytephysicalpropertiesandchemistry
6.5 This guide is intended to offer users a technically
as the project samples. If the match of the properties between
defensible strategy to determine the applicability of an analyti-
the project samples and the reference materials is poor, the
cal technique to a set of environmental samples.The complex-
study results can be misleading.
ity of the problem, the available resources (trained staff,
equipment, and time), and the intended use of the analytical 6.6.3 Option 3—The lack of availability of more than one
results require the application of professional judgment in analytical method (no alternative technology or resources) or
selecting the best available option to meet the project-specific of appropriate reference materials will prevent use of the
needs.Thefollowingsectionspresenttheuserwithavarietyof techniques mentioned above. When this is the case, the use of
optionstodeterminebias,precision,selectivity,andsensitivity. matrix spikes and surrogates becomes the “best available
The discussion of these options does not recommend one over technology” and can be a reliable option. As in all analytical
another. However, there are general principles that can assist studies, the analyst must support conclusions with scientific
the user in selecting an appropriate option. rationale, including the statistical basis of the number of
samples analyzed, the evaluation of experimental measure-
6.6 The laboratory should select the available option that
ments, and the limitations of the study.
will provide the information needed to determine if the
measurements meet the required level of quality (as defined by 6.6.3.1 Inorganic Matrix Spikes—While matrix spikes can
theuser/decisionmaker).Thenecessarylevelofqualityshould be a valuable tool in demonstrating the validity of the mea-
be
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