ASTM D4841-88(2003)
(Practice)Standard Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents
Standard Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents
SIGNIFICANCE AND USE
In order to obtain meaningful analytical data, sample preservation techniques must be effective from the time of sample collection to the time of analysis. A laboratory must confirm that sample integrity is maintained throughout maximum time periods between sample collection and analysis. In many cases, it is useful to know the maximum holding time. An evaluation of holding time is useful also in judging the efficacy of various preservation techniques.
SCOPE
1.1 This practice covers the means of estimating the period of time during which a water sample can be stored after collection and preservation without significantly affecting the accuracy of analysis.
1.2 The maximum holding time is dependent upon the matrix used and the specific analyte of interest. Therefore, water samples from a specific source must be tested to determine the period of time that sample integrity is maintained by standard preservation practices.
1.3 In the event that it is not possible to analyze the sample immediately at the time of collection, this practice does not provide information regarding degradation of the constituent of interest or changes in the matrix that may occur from the time of sample collection to the time of the initial analysis.
1.4 This standard does not purport to address all of the safety problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D 4841 – 88 (Reapproved 2003)
Standard Practice for
Estimation of Holding Time for Water Samples Containing
Organic and Inorganic Constituents
This standard is issued under the fixed designation D 4841; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope E 178 Practice for Dealing with Outlying Observations
1.1 This practice covers the means of estimating the period
3. Terminology
of time during which a water sample can be stored after
3.1 Definitions:
collection and preservation without significantly affecting the
3.1.1 For definitions of terms used in this practice, refer to
accuracy of analysis.
Terminology D 1129.
1.2 The maximum holding time is dependent upon the
3.1.2 criterion of detection—the minimum quantity that
matrix used and the specific analyte of interest. Therefore,
must be observed before it can be stated that a substance has
water samples from a specific source must be tested to
been discerned with an acceptable probability that the state-
determinetheperiodoftimethatsampleintegrityismaintained
ment is true (see Practice D 4210).
by standard preservation practices.
3.2 Definitions of Terms Specific to This Standard:
1.3 In the event that it is not possible to analyze the sample
3.2.1 maximum holding time—the maximum period of time
immediately at the time of collection, this practice does not
during which a properly preserved sample can be stored before
provideinformationregardingdegradationoftheconstituentof
such degradation of the constituent of interest or change in
interest or changes in the matrix that may occur from the time
sample matrix occurs that the systematic error exceeds the
of sample collection to the time of the initial analysis.
99 % confidence interval (not to exceed 15 %) of the test
1.4 This standard does not purport to address all of the
calculated around the mean concentration found at zero time.
safety concerns, if any, associated with its use. It is the
3.2.2 acceptable holding time—any period of time less than
responsibility of the user of this standard to establish appro-
or equal to the maximum holding time.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
4. Summary of Practice
2. Referenced Documents 4.1 Holding time is estimated by means of replicate analy-
ses at discrete time intervals using a large volume of a water
2.1 ASTM Standards:
2 sample that has been properly collected and preserved. A
D 1129 Terminology Relating to Water
sufficient number of replicate analyses are performed to main-
D 1192 Specification for Equipment for Sampling Water
2 tain the 99 % confidence interval within 15 % of the concen-
and Steam in Closed Conduits
2 tration found at zero time. Concentration of the constituent of
D 1193 Specification for Reagent Water
interest is plotted versus time. The maximum holding time is
D 2777 Practice for Determination of Precision and Bias of
2 the period of time from sample collection to such time that
Applicable Methods of Committee D-19 on Water
degradation of the constituent of interest or change in sample
D 3694 Practices for Preparation of Sample Containers and
3 matrix occurs and the systematic error exceeds the 99 %
for Preservation of Organic Constituents
confidence interval (not to exceed 15 %) of the test calculated
D 4210 Practice for Intralaboratory Quality Control Proce-
2 around the mean concentration at zero time. Prior to the
dures and a Discussion on Reporting Low-Level Data
determination of holding time, each laboratory must generate
D 4375 Practice for Basic Statistics in Committee D-19 on
2 itsownprecisiondatainmatrixwater.Thesedataarecompared
Water
to the pooled single-operator precision data on reagent water
reported in the test method and, the less precise of the two sets
This practice is under the jurisdiction of ASTM Committee D19 on Water and
of data are used in the calculation.
is the direct responsibility of Subcommittee D19.02 on General Specifications,
NOTE 1—This practice generates only limited data which may not lead
Technical Resources, and Statistical Methods.
Current edition approved Aug. 10, 2003. Published November 2003. Originally to consistent conclusions each time that the test is applied. In cases where
approved in 1988. Last previous edition approved in 1998 as D 4841 – 88 (1998).
Annual Book of ASTM Standards, Vol 11.01.
Annual Book of ASTM Standards, Vol 11.02.
Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 4841 – 88 (2003)
the concentration of the constituent of interest changes gradually over an
B = estimated number of replicate determinations required
extended period of time, the inherent variability in test results may lead to
at each interval in the holding time study (see Table
somewhat different conclusions each time that this practice is applied.
1),
C = estimated number of time intervals required for the
5. Significance and Use
holding time study (excluding the initial time zero
5.1 In order to obtain meaningful analytical data, sample
precision study), and
preservation techniques must be effective from the time of
D = number of replicate determinations performed in ini-
sample collection to the time of analysis. A laboratory must
tial precision study (usually 10).
confirm that sample integrity is maintained throughout maxi-
7.1.2 Based on the volume calculated in 7.1.1, collect a
mum time periods between sample collection and analysis. In
sufficient volume of the specific matrix to be tested to perform
manycases,itisusefultoknowthemaximumholdingtime.An
a precision study and the holding time study. Collect the
evaluation of holding time is useful also in judging the efficacy
sample in a properly prepared sample container or series of
of various preservation techniques.
containers.Refertotheprocedurefortheconstituentofinterest
for specific instructions on sample collection procedures.
6. Reagents
NOTE 3—The total volume of sample calculated in 7.1.1 is only an
6.1 Purity of Reagents—Reagent grade chemicals shall be
estimate.Dependinguponthedegreeofcertaintywithwhichtheprecision
used in all tests. Unless otherwise indicated, it is intended that
can be estimated, it is recommended that a volume somewhat in excess of
all reagents shall conform to the specifications of the Commit-
that calculated in 7.1.1 be collected in order to make certain that sufficient
tee onAnalytical Reagents of theAmerican Chemical Society,
sample will be available to complete the holding time study. The analyst
where such specifications are available. Other grades may be
may want to consider performing a preliminary precision study prior to
sample collection in order to be certain that the estimate of precision used
used provided it is first ascertained that the reagent is of
in 7.1.1 is reasonably accurate.
sufficiently high purity to permit its use without lowering the
accuracy of the determination.
7.1.3 Add the appropriate preservation reagents to the
6.1.1 Refer to the specific test method and to Practices
sample immediately after collection. Immediately proceed to
D 3694 for information regarding necessary equipment and 7.2 or 7.3 depending upon whether inorganic or organic
preparation of reagents.
compounds are being determined.
6.2 PurityofWater—Referencetowatershallbeunderstood 7.2 Determination of Single Operator Precision—Inorganic
to mean reagent water conforming to Specification D 1193,
Methods:
TypeII,anddemonstratedtobefreeofspecificinterferencefor 7.2.1 Immediately after sample collection, analyze an ap-
the test being performed.
propriate number (usually 10) of measured volumes of sample
as described in the appropriate procedure. If a measurable
7. Determination of Holding Time
concentration of the constituent of interest is found, proceed to
7.2.4.Iftheconcentrationoftheconstituentofinterestisbelow
7.1 Collection of Sample:
the criterion of detection at a P level of# 0.05, fortify the
NOTE 2—In some instances, it may be of interest to determine the
sample as described in 7.2.2 and reanalyze or collect another
holdingtimeofstandardsolutionspreparedinwater.Insuchcases,alarge
sample.
volume of properly preserved, standard solution should be prepared and
carried through the steps of the practice in the same manner as a sample.
NOTE 4—If the concentration of the constituent of interest is very low
The volume of solution required can be estimated using the equation in
suchthatitapproachesthecriterionofdetectionata Plevelof#0.05,the
7.1.1.
precision will be very poor.At such very low concentrations, a fairly large
number of replicate determinations will be required to bring the 99 %
7.1.1 Based on the estimated precision of the test (deter-
confidenceintervaltowithin15 %oftheconcentrationfound.Underthese
mined from past experience or from precision data reported in
circumstances, it may be desirable to fortify the sample with the
the test method), calculate the estimated total volume of
constituent of interest to increase the concentration to a point where the
samplerequiredtoperformtheholdingtimedeterminationplus
precision will be improved and fewer replicates will be required for the
a precision study. Estimate this volume as follows:
holdingtimedetermination.However,theholdingtimemaybedifferentat
V 5 ~A 3 B 3 C! 1 2 ~A 3 D!
(1)
TABLE 1 Approximate Number of Replicate Determinations
Required at Each Interval in the Holding Time Study Based on
where:
the Estimated Relative Standard Deviation of the Test in the
V = estimated volume of sample required, mL,
Matrix Under Study
A = volume of sample required to perform each separate
Estimated RSD, % Approximate Number of Replicates
analysis, mL,
1–4 1
5–6 2
7–8 3
10 5
Reagent Chemicals, American Chemical Society Specifications, American
11 6
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
12 7
listed by the American Chemical Society, see Analar Standards for Laboratory
13 8
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
14 10
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, 15 11
MD.
D 4841 – 88 (2003)
the higher concentration than it would be at the lower concentration. This
measurable concentration of the constituent of interest is
decision is left to the judgement of the analyst.
found,proceedto7.3.3.5.Ifnot,fortifythesampleasdescribed
in 7.3.3.3 and reanalyze (see Note 4).
7.2.2 Accurately measure the volume of the remainder of
7.3.3.3 Fortify the sample in all of the remaining glass
the sample and fortify with a known concentration of the
bottles with a known concentration of the constituent of
constituent of interest.
interest by adding an accurately measured small volume of a
7.2.3 Immediately perform an appropriate number (usually
concentrated standard solution of the analyte.
10) of replicate analyses of the sample as described in the
7.3.3.4 Immediately perform an appropriate number (usu-
appropriate procedure.
ally 10) of replicate analyses of the fortified sample as
7.2.4 Calculate the mean concentration, the standard devia-
described in the appropriate procedure.
tion, and relative standard deviation of these replicate deter-
7.3.3.5 Calculate the mean concentration, the standard de-
minations (see Practice D 4375). Proceed to 8.1.
viation, and the relative standard deviation of these replicate
7.3 Determination of Single-Operator Precision—Organic
determinations (see Practice D 4375). Proceed to 8.1.
Methods:
7.3.4 Purgeable Organic Compounds:
7.3.1 General Organic Constituent Methods—Immediately
7.3.4.1 Immediately after collection, perform an appropriate
after sample collection, analyze an appropriate number (usu-
number(usually10)ofreplicatedeterminationsoftheconstitu-
ally 10) of measured volumes of sample as described in the
ent of interest by analyzing separate aliquots of sample that
appropriate procedure. If a measurable concentration of organ-
have been collected in hermetically sealed containers. If a
ics is found, proceed to 7.3.1.1. If the concentration of the
measurable concentration is found, proceed to 7.3.4.3.Ifthe
organic compounds is below the criterion of detection at a P
concentration is below the criterion of detection at a P level of
level of# 0.05, collect another sample and repeat the analysis
# 0.05, either fortify the sample as described in 7.3.4.2 or
until a sample containing a measurable concentration is ob-
collect another sample and repeat the analysis (see Note 4).
tained (see Note 4).
7.3.4.2 If the sample requires fortification, open all of the
NOTE 5—Since there is no way of positively identifying all of the
remaining containers and transfer the contents to a graduated
compounds that may be contributing to the values found in the general
cylinder to measure the total volume of the remaining sample.
organic constituent methods, the sample cannot be fortified. To carry out
Then transfer the sample to an aspirator bottle fitted with a
the holding time determination, a sample must be obtained that contains a
stopcock at the bottom. Transfer, by means of a syringe, a
measurable concentration of organics in order to carry out the study.
measured volume of stock solution containing a known con-
7.3.1.1 Calculate the mean concentration, the standard de-
centration of the constituent of interest into the sample. The
viation, and the relative standard deviation of these replicate
syringe needle should be below the surface of the liquid during
determinations (see Practice D 4375). Proceed to 8.1.
the transfer. Stopper the bottle and mix well. Carefully transfer
7.3.2 Specific Organic Constituent Methods (Applicable to
(bydrainingthroughthestopcock)thesampletoseparatesmall
methodsthatdonotrequireextractionofthesamplecontainer):
glass vials. Take care to carry out the sample transfer with a
7.3.2.1 Immediately after sample collection, analyze an
minimum of sample agitation and aeration. Fill each sample
appropriate number (usually 10) of measured volumes of
vial to overflowing so that a convex meniscus forms at the top.
sample as determined in the appropriate procedure. If a
Seal each vial as described in Practices D 3694.
measurable concentration of the constituent of interest is
NOTE 6—It is recommended that the operator’s technique used in
found, proceed to 7.3.2.4. If not, either collect another sample
transferring solutions of purgeabl
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.