1、Designation: D4841 88 (Reapproved 2013)Standard Practice forEstimation of Holding Time for Water Samples ContainingOrganic and Inorganic Constituents1This standard is issued under the fixed designation D4841; the number immediately following the designation indicates the year oforiginal adoption or,
2、 in the case of revision, the year of last revision. 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 covers the means of estimating the periodof time during which a wa
3、ter 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 period o
4、f 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 tha
5、t may occur from the timeof sample collection to the time of the initial analysis.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated wi
6、th 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 Standards:2D1129 Terminology Relating to WaterD1192 Guide for Equipment for S
7、ampling Water and Steamin Closed Conduits (Withdrawn 2003)3D1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3694 Practices for Preparation of Sample Containers andfor Preservation of Organic ConstituentsD4
8、210 Practice for Intralaboratory Quality Control Proce-dures and a Discussion on Reporting Low-Level Data(Withdrawn 2002)3D4375 Practice for Basic Statistics in Committee D19 onWaterE178 Practice for Dealing With Outlying Observations3. Terminology3.1 Definitions:3.1.1 For definitions of terms used
9、in this practice, refer toTerminology D1129.3.1.2 criterion of detectionthe minimum quantity thatmust be observed before it can be stated that a substance hasbeen discerned with an acceptable probability that the state-ment is true (see Practice D4210).3.2 Definitions of Terms Specific to This Stand
10、ard:3.2.1 maximum holding timethe maximum period of timeduring which a properly preserved sample can be stored beforesuch degradation of the constituent of interest or change insample matrix occurs that the systematic error exceeds the99 % confidence interval (not to exceed 15 %) of the testcalculat
11、ed around the mean concentration found at zero time.3.2.2 acceptable holding timeany period of time less thanor equal to the maximum holding 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
12、has been properly collected and preserved. Asufficient number of replicate analyses are performed to main-tain the 99 % confidence interval 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
13、of time from sample collection to such time thatdegradation of the constituent of interest or change in samplematrix occurs and the systematic error exceeds the 99 %confidence interval (not to exceed 15 %) of the test calculatedaround the mean concentration at zero time. Prior to the1This practice i
14、s under the jurisdiction of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.02 on Quality Systems,Specification, and Statistics.Current edition approved Jan. 1, 2013. Published January 2013. Originallyapproved in 1988. Last previous edition approved in 2008 as D4841 8
15、8 (2008).DOI: 10.1520/D4841-88R13.2For 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.3The last approved version
16、of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1determination of holding time, each laboratory must generateits own precision data in matrix water. These data are comparedto the
17、 pooled single-operator 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 whereth
18、e concentration of the constituent 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, sample
19、preservation techniques must be 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.Aneva
20、luation of holding time is useful 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 An
21、alytical Reagents of the American Chemical Society,where such specifications are available.4Other 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 met
22、hod and to PracticesD3694 for information regarding necessary equipment andpreparation of reagents.6.2 Purity of Water Reference to water shall be under-stood to mean reagent water conforming to SpecificationD1193, Type II, and demonstrated to be free of specificinterference for the test being perfo
23、rmed.7. Determination of Holding 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
24、the practice in the same manner 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 ofsamp
25、le required to perform the holding time determination plusa precision study. Estimate this volume as follows:V 5 A 3B 3C!12 A 3D! (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 r
26、equiredat each interval in the holding time study (see Table 1),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
27、volume calculated in 7.1.1, 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 inst
28、ructions on sample collection 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 ma
29、ke certain that sufficientsample 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 appropriat
30、e preservation reagents to thesample 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-propri
31、ate number (usually 10) of measured 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
32、thesample as described in 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
33、 replicate determinations 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
34、and fewer replicates will be required for theholding time determination. However, the holding time may be different atthe higher concentration than it would be at the lower concentration. Thisdecision is left to the judgement of the analyst.7.2.2 Accurately measure the volume of the remainder ofthe
35、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 concentration, the standarddeviation, and relative standard de
36、viation of these replicatedeterminations (see Practice D4375). Proceed to 8.1.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for Labora
37、toryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D4841 88 (Reapproved 2013)27.3 Determination of Single-Operator PrecisionOrganicMethods:7.3.1 General Organic Constituent MethodsImmediatel
38、yafter sample collection, analyze an appropriate number (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
39、 Plevel of 0.05, collect another sample and repeat 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 metho
40、ds, the sample cannot be fortified. To carry outthe 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 standarddeviation, and the relative standard deviation of these
41、replicatedeterminations (see Practice D4375). 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
42、 determined in the appropriate procedure. If 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
43、 sample and fortify it with a known concentration 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 standarddeviation, and
44、the relative standard deviation of these replicatedeterminations (see Practice D4375). 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, im
45、mediately transfer shaken, 1-L portions ofthe sample to separate properly prepared (see Practices D3694)litre glass bottles which have had the litre mark placed on theneck of the container.7.3.3.2 Immediately perform an appropriate number (usu-ally 10) of replicate determinations of the constituent
46、ofinterest by analyzing the sample in the 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 con
47、centration of the constituent ofinterest 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 Calc
48、ulate the mean concentration, the standarddeviation, and the relative standard deviation of these replicatedeterminations (see Practice D4375). Proceed to 8.1.7.3.4 Purgeable Organic Compounds :7.3.4.1 Immediately after collection, perform an appropriatenumber (usually 10) of replicate determination
49、s of the constitu-ent of interest by analyzing 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.The
