1、Designation: D 4841 88 (Reapproved 2003)Standard Practice forEstimation of Holding Time for Water Samples ContainingOrganic and Inorganic Constituents1This standard is issued under the fixed designation D 4841; the number immediately following the designation indicates the year oforiginal adoption o
2、r, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the means of estimating the periodof time during which a
3、 water sample can be stored aftercollection and preservation without significantly affecting theaccuracy of analysis.1.2 The maximum holding time is dependent upon thematrix used and the specific analyte of interest. Therefore,water samples from a specific source must be tested todetermine the perio
4、d of time that sample integrity is maintainedby standard preservation practices.1.3 In the event that it is not possible to analyze the sampleimmediately at the time of collection, this practice does notprovide information regarding degradation of the constituent ofinterest or changes in the matrix
5、that may occur from the timeof sample collection to the time of the initial analysis.1.4 This standard does 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 an
6、d determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:D 1129 Terminology Relating to Water2D 1192 Specification for Equipment for Sampling Waterand Steam in Closed Conduits2D 1193 Specification for Reagent Water2D 2777 Practice for Determinat
7、ion of Precision and Bias ofApplicable Methods of Committee D-19 on Water2D 3694 Practices for Preparation of Sample Containers andfor Preservation of Organic Constituents3D 4210 Practice for Intralaboratory Quality Control Proce-dures and a Discussion on Reporting Low-Level Data2D 4375 Practice for
8、 Basic Statistics in Committee D-19 onWater2E 178 Practice for Dealing with Outlying Observations43. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this practice, refer toTerminology D 1129.3.1.2 criterion of detectionthe minimum quantity thatmust be observed before it can be stat
9、ed that a substance hasbeen discerned with an acceptable probability that the state-ment is true (see Practice D 4210).3.2 Definitions of Terms Specific to This Standard:3.2.1 maximum holding timethe maximum period of timeduring which a properly preserved sample can be stored beforesuch degradation
10、of the constituent of interest or change insample matrix occurs that the systematic error exceeds the99 % confidence interval (not to exceed 15 %) of the testcalculated around the mean concentration found at zero time.3.2.2 acceptable holding timeany period of time less thanor equal to the maximum h
11、olding time.4. Summary of Practice4.1 Holding time is estimated by means of replicate analy-ses at discrete time intervals using a large volume of a watersample that has been properly collected and preserved. Asufficient number of replicate analyses are performed to main-tain the 99 % confidence int
12、erval within 15 % of the concen-tration found at zero time. Concentration of the constituent ofinterest is plotted versus time. The maximum holding time isthe period of time from sample collection to such time thatdegradation of the constituent of interest or change in samplematrix occurs and the sy
13、stematic error exceeds the 99 %confidence interval (not to exceed 15 %) of the test calculatedaround the mean concentration at zero time. Prior to thedetermination of holding time, each laboratory must generateits own precision data in matrix water. These data are comparedto the pooled single-operat
14、or precision data on reagent waterreported in the test method and, the less precise of the two setsof data are used in the calculation.NOTE 1This practice generates only limited data which may not leadto consistent conclusions each time that the test is applied. In cases where1This practice is under
15、 the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.02 on General Specifications,Technical Resources, and Statistical Methods.Current edition approved Aug. 10, 2003. Published November 2003. Originallyapproved in 1988. Last previous edition approved i
16、n 1998 as D 4841 88 (1998).2Annual Book of ASTM Standards, Vol 11.01.3Annual Book of ASTM Standards, Vol 11.02.4Annual Book of ASTM Standards, Vol 14.02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the concentration of the constit
17、uent of interest changes gradually over anextended period of time, the inherent variability in test results may lead tosomewhat different conclusions each time that this practice is applied.5. Significance and Use5.1 In order to obtain meaningful analytical data, samplepreservation techniques must b
18、e effective from the time ofsample collection to the time of analysis. A laboratory mustconfirm that sample integrity is maintained throughout maxi-mum time periods between sample collection and analysis. Inmany cases, it is useful to know the maximum holding time.Anevaluation of holding time is use
19、ful also in judging the efficacyof various preservation techniques.6. Reagents6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the Ameri
20、can Chemical Society,where such specifications are available.5Other grades may beused provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lowering theaccuracy of the determination.6.1.1 Refer to the specific test method and to PracticesD 3694 for
21、 information regarding necessary equipment andpreparation of reagents.6.2 Purity of WaterReference to water shall be understoodto mean reagent water conforming to Specification D 1193,Type II, and demonstrated to be free of specific interference forthe test being performed.7. Determination of Holdin
22、g Time7.1 Collection of Sample:NOTE 2In some instances, it may be of interest to determine theholding time of standard solutions prepared in water. In such cases, a largevolume of properly preserved, standard solution should be prepared andcarried through the steps of the practice in the same manner
23、 as a sample.The volume of solution required can be estimated using the equation in7.1.1.7.1.1 Based on the estimated precision of the test (deter-mined from past experience or from precision data reported inthe test method), calculate the estimated total volume ofsample required to perform the hold
24、ing time determination plusa precision study. Estimate this volume as follows:V 5 A 3 B 3 C! 1 2 A 3 D!(1)where:V = estimated volume of sample required, mL,A = volume of sample required to perform each separateanalysis, mL,B = estimated number of replicate determinations requiredat each interval in
25、the holding time study (see Table1),C = estimated number of time intervals required for theholding time study (excluding the initial time zeroprecision study), andD = number of replicate determinations performed in ini-tial precision study (usually 10).7.1.2 Based on the volume calculated in 7.1.1,
26、collect asufficient volume of the specific matrix to be tested to performa precision study and the holding time study. Collect thesample in a properly prepared sample container or series ofcontainers. Refer to the procedure for the constituent of interestfor specific instructions on sample collectio
27、n procedures.NOTE 3The total volume of sample calculated in 7.1.1 is only anestimate. Depending upon the degree of certainty with which the precisioncan be estimated, it is recommended that a volume somewhat in excess ofthat calculated in 7.1.1 be collected in order to make certain that sufficientsa
28、mple will be available to complete the holding time study. The analystmay want to consider performing a preliminary precision study prior tosample collection in order to be certain that the estimate of precision usedin 7.1.1 is reasonably accurate.7.1.3 Add the appropriate preservation reagents to t
29、hesample immediately after collection. Immediately proceed to7.2 or 7.3 depending upon whether inorganic or organiccompounds are being determined.7.2 Determination of Single Operator PrecisionInorganicMethods:7.2.1 Immediately after sample collection, analyze an ap-propriate number (usually 10) of m
30、easured volumes of sampleas described in the appropriate procedure. If a measurableconcentration of the constituent of interest is found, proceed to7.2.4. If the concentration of the constituent of interest is belowthe criterion of detection at a P level of # 0.05, fortify thesample as described in
31、7.2.2 and reanalyze or collect anothersample.NOTE 4If the concentration of the constituent of interest is very lowsuch that it approaches the criterion of detection at a P level of#0.05, theprecision will be very poor.At such very low concentrations, a fairly largenumber of replicate determinations
32、will be required to bring the 99 %confidence interval to within 15 % of the concentration found. Under thesecircumstances, it may be desirable to fortify the sample with theconstituent of interest to increase the concentration to a point where theprecision will be improved and fewer replicates will
33、be required for theholding time determination. However, the holding time may be different at5Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standa
34、rds for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.TABLE 1 Approximate Number of Replicate DeterminationsRequired at Each Interval in the Holding Time Study Based onthe Estimat
35、ed Relative Standard Deviation of the Test in theMatrix Under StudyEstimated RSD, % Approximate Number of Replicates14 156 278 39410 511 612 713 814 1015 11D 4841 88 (2003)2the higher concentration than it would be at the lower concentration. Thisdecision is left to the judgement of the analyst.7.2.
36、2 Accurately measure the volume of the remainder ofthe sample and fortify with a known concentration of theconstituent of interest.7.2.3 Immediately perform an appropriate number (usually10) of replicate analyses of the sample as described in theappropriate procedure.7.2.4 Calculate the mean concent
37、ration, the standard devia-tion, and relative standard deviation of these replicate deter-minations (see Practice D 4375). Proceed to 8.1.7.3 Determination of Single-Operator PrecisionOrganicMethods:7.3.1 General Organic Constituent MethodsImmediatelyafter sample collection, analyze an appropriate n
38、umber (usu-ally 10) of measured volumes of sample as described in theappropriate procedure. If a measurable concentration of organ-ics is found, proceed to 7.3.1.1. If the concentration of theorganic compounds is below the criterion of detection at a Plevel of # 0.05, collect another sample and repe
39、at the analysisuntil a sample containing a measurable concentration is ob-tained (see Note 4).NOTE 5Since there is no way of positively identifying all of thecompounds that may be contributing to the values found in the generalorganic constituent methods, the sample cannot be fortified. To carry out
40、the holding time determination, a sample must be obtained that contains ameasurable concentration of organics in order to carry out the study.7.3.1.1 Calculate the mean concentration, the standard de-viation, and the relative standard deviation of these replicatedeterminations (see Practice D 4375).
41、 Proceed to 8.1.7.3.2 Specific Organic Constituent Methods (Applicable tomethods that do not require extraction of the sample container):7.3.2.1 Immediately after sample collection, analyze anappropriate number (usually 10) of measured volumes ofsample as determined in the appropriate procedure. If
42、ameasurable concentration of the constituent of interest isfound, proceed to 7.3.2.4. If not, either collect another sampleor fortify the sample as described in 7.3.2.2 and reanalyze (seeNote 4).7.3.2.2 Accurately measure the volume of the remainder ofthe sample and fortify it with a known concentra
43、tion of theconstituent of interest.7.3.2.3 Immediately perform an appropriate number (usu-ally 10) of replicate analyses of the fortified sample asdescribed in the appropriate procedure.7.3.2.4 Calculate the mean concentration, the standard de-viation, and the relative standard deviation of these re
44、plicatedeterminations (see Practice D 4375). Proceed to 8.1.7.3.3 Specific Organic Constituent Methods (Applicable tomethods that require extraction of the sample container):7.3.3.1 If the sample was collected in a container other thanlitre glass bottles, immediately transfer shaken, 1-L portions of
45、the sample to separate properly prepared (see PracticesD 3694) litre glass bottles which have had the litre mark placedon the neck of the container.7.3.3.2 Immediately perform an appropriate number (usu-ally 10) of replicate determinations of the constituent ofinterest by analyzing the sample in the
46、 containers. If ameasurable concentration of the constituent of interest isfound, proceed to 7.3.3.5. If not, fortify the sample as describedin 7.3.3.3 and reanalyze (see Note 4).7.3.3.3 Fortify the sample in all of the remaining glassbottles with a known concentration of the constituent ofinterest
47、by adding an accurately measured small volume of aconcentrated standard solution of the analyte.7.3.3.4 Immediately perform an appropriate number (usu-ally 10) of replicate analyses of the fortified sample asdescribed in the appropriate procedure.7.3.3.5 Calculate the mean concentration, the standar
48、d de-viation, and the relative standard deviation of these replicatedeterminations (see Practice D 4375). Proceed to 8.1.7.3.4 Purgeable Organic Compounds:7.3.4.1 Immediately after collection, perform an appropriatenumber (usually 10) of replicate determinations of the constitu-ent of interest by an
49、alyzing separate aliquots of sample thathave been collected in hermetically sealed containers. If ameasurable concentration is found, proceed to 7.3.4.3.Iftheconcentration is below the criterion of detection at a P level of# 0.05, either fortify the sample as described in 7.3.4.2 orcollect another sample and repeat the analysis (see Note 4).7.3.4.2 If the sample requires fortification, open all of theremaining containers and transfer the contents to a graduatedcylinder to measure the total volume of the remaining sample.Then transfer the sample to an aspirator bottle
