1、Designation: D4841 88 (Reapproved 2013)1Standard 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.1NOTEEditorial corrections made throughout in August 2013.1. Scope1.1 This practice covers
3、the means of estimating the periodof time during which a 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 fro
4、m a specific source must be tested todetermine the period 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
5、 of the constituent ofinterest or changes in the matrix that 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
6、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 and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1129 T
7、erminology Relating to WaterD1192 Guide for Equipment for Sampling Water and Steamin Closed Conduits (Withdrawn 2003)3D1193 Specification for Reagent WaterD2777 Practice for Determination of Precision and Bias ofApplicable Test Methods of Committee D19 on WaterD3694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 Samp
8、le Containers andfor Preservation of Organic ConstituentsD4210 Practice for Intralaboratory Quality Control Proce-dures and a Discussion on Reporting Low-Level Data(Withdrawn 2002)3D4375 Practice for Basic Statistics in Committee D19 onWaterE178 Practice for Dealing With Outlying Observations3. Term
9、inology3.1 DefinitionsFor definitions of terms used in thispractice, refer to Terminology D1129.3.1.1 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 D4
10、210).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 of the constituent of interest or change insample matrix occurs that the systematic error exceeds the99 % confiden
11、ce 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 holding time.4. Summary of Practice4.1 Holding time is estimated by means of replicate analy-ses at discrete time i
12、ntervals 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 interval within 15 % of the concen-tration found at zero time. Concentration of the constituent of1This practice is u
13、nder 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 88 (
14、2008).DOI: 10.1520/D4841-88R13E01.2For 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
15、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 States1interest is plotted versus time. The maximum holding time isthe period of time from sample collection to such time thatdegradatio
16、n 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 thedetermination of holding time, each laboratory must generateits own precis
17、ion 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 setsof data are used in the calculation.NOTE 1This practice generates only limited data which may not leadto consistent conclusio
18、ns 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 variability in test results may lead tosomewhat different conclusions each time that this practice is applied.5. Significance and Use5.
19、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 mustconfirm that sample integrity is maintained throughout maxi-mum time periods between sample collection and analysis. Inmany cas
20、es, 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 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shal
21、l 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 provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lowering theaccuracy of
22、 the determination.6.1.1 Refer to the specific test method and to PracticesD3694 for information regarding necessary equipment andpreparation of reagents.6.2 Purity of WaterReference to water shall be understoodto mean reagent water conforming to Specification D1193,Type II, and demonstrated to be f
23、ree 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 determine theholding time of standard solutions prepared in water. In such cases, a largevolume of properly preserved, standard solution
24、 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 in7.1.1.7.1.1 Based on the estimated precision of the test (deter-mined from past experience or from precision data reported inthe test
25、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 3B 3C!12 A 3D! (1)where:V = estimated volume of sample required, mL,A = volume of sample required to perform each separateanalysis, m
26、L,B = estimated number of replicate determinations requiredat 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 initi
27、alprecision 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 study and the holding time study. Collect thesample in a properly prepared sample container or series ofcontainers. Refer to the procedur
28、e 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. Depending upon the degree of certainty with which the precisioncan be estimated, it is recommended that a volume somewhat in excess ofth
29、at 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 consider performing a preliminary precision study prior tosample collection in order to be certain that the estimate of precision usedin 7.1
30、.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 upon whether inorganic or organiccompounds are being determined.7.2 Determination of Single Operator PrecisionInorganicMethods:7.2.1 Immedia
31、tely after sample collection, analyze an ap-propriate 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 below4Reagen
32、t Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC, www.chemistry.org. For suggestions on thetesting of reagents not listed by the American Chemical Society, see AnalarStandards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and theUnited States
33、 Pharmacopeia and National Formulary, U.S. PharmacopeialConvention, Inc. (USPC), Rockville, MD, http:/www.usp.org.TABLE 1 Approximate Number of Replicate DeterminationsRequired at Each Interval in the Holding Time Study Based onthe Estimated Relative Standard Deviation of the Test in theMatrix Under
34、 StudyEstimated RSD, % Approximate Number of Replicates14 156 278 39410 511 612 713 814 1015 11D4841 88 (2013)12the 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 constituent of interest is
35、 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 will be required to bring the 99 %confidence interval to within 15 % of the concentration found. Under th
36、esecircumstances, 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 required for theholding time determination. However, the holding time may be different atthe higher co
37、ncentration 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 known concentration of theconstituent of interest.7.2.3 Immediately perform an appropriate number (usuall
38、y10) of replicate analyses of the sample as described in theappropriate procedure.7.2.4 Calculate the mean concentration, the standarddeviation, and relative standard deviation of these replicatedeterminations (see Practice D4375). Proceed to 8.1.7.3 Determination of Single-Operator PrecisionOrganic
39、Methods: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 procedure. If a measurable concentration of organ-ics is found, proceed to 7.3.1.1. If the concentration of th
40、eorganic 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 Note 4).NOTE 5Since there is no way of positively identifying all of thecompounds that may be contributing
41、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 concentration of organics in order to carry out the study.7.3.1.1 Calculate the mean concentration, the stand
42、arddeviation, and the relative standard deviation of these 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 anappro
43、priate 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. If not, either collect another sampleor fortify the sample as described in 7.3.2.2 and reanalyze (seeNote 4).7.
44、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 (usu-ally 10) of replicate analyses of the fortified sample asdescribed in the appropriate procedure.7.3.2.4 Cal
45、culate the mean concentration, the standarddeviation, and 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 c
46、ollected in a container other thanlitre glass bottles, immediately 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
47、-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, 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 sam
48、ple 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 the analyte.7.3.3.4 Immediately perform an appropriate number (usu-ally 10) of replicate analyses of the fortified sam
49、ple asdescribed in the appropriate procedure.7.3.3.5 Calculate 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 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.Iftheconcent
