1、Designation: D 4841 88 (Reapproved 2008)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 () 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 period
4、 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 t
5、hat 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
6、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 Standards:2D 1129 Terminology Relating to WaterD 1192 Guide for Equipment f
7、or Sampling Water andSteam in Closed Conduits3D 1193 Specification for Reagent WaterD 2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD 3694 Practices for Preparation of Sample Containers andfor Preservation of Organic ConstituentsD 4210 Pract
8、ice for Intralaboratory Quality Control Proce-dures and a Discussion on Reporting Low-Level Data3D 4375 Practice for Basic Statistics in Committee D19 onWaterE 178 Practice for Dealing With Outlying Observations3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this practice, refer
9、 toTerminology D 1129.3.1.2 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 D 4210).3.2 Definitions of Terms Specific to This Standard:3.2.1 maximum hol
10、ding 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 testcalculated around the mean co
11、ncentration 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 has been properly col
12、lected 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 of time from sample c
13、ollection 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 is under the jurisdict
14、ion of ASTM Committee D19 on Water andis the direct responsibility of Subcommittee D19.02 on Quality Systems, Specifi-cation, and Statistics.Current edition approved July 15, 2008. Published August 2008. Originallyapproved in 1988. Last previous edition approved in 2003 as D 4841 88 (2003).2For refe
15、renced 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.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Bo
16、x C700, West Conshohocken, PA 19428-2959, United States.determination of holding time, each laboratory must generateits own precision data in matrix water. These data are comparedto the pooled single-operator precision data on reagent waterreported in the test method and, the less precise of the two
17、 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 wherethe concentration of the constituent of interest changes gradually over anextended period of time, the inherent varia
18、bility 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 be effective from the time ofsample collection to the time of analysis. A laboratory m
19、ustconfirm 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 useful also in judging the efficacyof various preservation techniques.6. Reagents6.1 Pur
20、ity 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 American Chemical Society,where such specifications are available.4Other grades may beused
21、 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 information regarding necessary equipment andpreparation of reagents.6.2 Purity of W
22、aterReference 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 Holding Time7.1 Collection of Sample:NOTE 2In some instances, it may be of interest to dete
23、rmine 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 as a sample.The volume of solution required can be estimated using the equation in7.
24、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 holding time determination plusa precision study. Estimate this volume as follows:V 5 A 3
25、 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 the holding time study (see Table1),C = estimated number of time intervals required f
26、or 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, collect asufficient volume of the specific matrix to be tested to performa precision
27、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 collection procedures.NOTE 3The total volume of sample calculated in 7.1.1 is only anestimate.
28、 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 sufficientsample will be available to complete the holding time study. The analystmay want to con
29、sider 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 thesample immediately after collection. Immediately proceed to7.2 or 7.3 depending upo
30、n 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 measured volumes of sampleas described in the appropriate procedure. If a measurableco
31、ncentration 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 7.2.2 and reanalyze or collect anothersample.NOTE 4If the concentration of the consti
32、tuent of interest is very lowsuch that it approaches the criterion of detection at a P level of#0.05, the4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see
33、Annual Standards 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
34、onthe Estimated 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 (2008)2precision will be very poor.At such very low concentrations, a fairly largenumber of replicate determinations will
35、 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 be r
36、equired 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 sample and fortify with a know
37、n 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 standard devia-tion, and relative standard deviation of these replicate d
38、eter-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 number (usu-ally 10) of measured volumes of sample as described in theappropriate proc
39、edure. 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 repeat the analysisuntil a sample containing a measurable concentration is ob-tained (see
40、 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 outthe holding time determination, a sample must be obtained that contains ameasurable c
41、oncentration 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). Proceed to 8.1.7.3.2 Specific Organic Constituent Methods (Applicable tomethods that
42、 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 ameasurable concentration of the constituent of interest isfound, proceed to 7.3.2.4.
43、 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 concentration of theconstituent of interest.7.3.2.3 Immediately perform an appropriate number
44、(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 replicatedeterminations (see Practice D 4375). Proceed to 8.1.7.3.3 Specific Organic Co
45、nstituent 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 ofthe sample to separate properly prepared (see PracticesD 3694) litre glass bottles wh
46、ich 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 containers. If ameasurable concentration of the constituent of interest isfound, pro
47、ceed 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 by adding an accurately measured small volume of aconcentrated standard solution of t
48、he 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 standard de-viation, and the relative standard deviation of these replicatedeterminations (s
49、ee 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 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 th
