1、Designation: E 882 87 (Reapproved 2003)Standard Guide forAccountability and Quality Control in the ChemicalAnalysis Laboratory1This standard is issued under the fixed designation E 882; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisio
2、n, 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 guide covers the essential aspects of an account-ability and quality control program for a chemic
3、al analysislaboratory. The reasons for establishing and operating such aprogram are discussed.2. Referenced Documents2.1 ASTM Standards:MNL 7 Manual on Presentation of Data and Control ChartAnalysis22.2 ANSI Document:ANSI/ASQC A1 Definitions, Symbols, Formulas, andTables for Control Charts33. Signif
4、icance and Use3.1 An accountability and quality control system is estab-lished by laboratory management to improve the quality of itsresults. It provides documented records which serve to assureusers of the laboratorys services that a specified level ofprecision is achieved in the routine performanc
5、e of its mea-surements and that the data reported were obtained from thesamples submitted. The system also provides for: early warn-ing to analysts when methods or equipment begin to develop abias or show deterioration of precision; the protection andretrievability of data (results); traceability an
6、d control ofsamples as they are processed through the laboratory; goodcommunication of sample information between submitters,analysts, and supervision; and information on sample process-ing history. This guide describes such a system. Other account-ability and quality control programs can be develop
7、ed. Suchprograms can be equivalent to the program in this guide if theyprovide all of the benefits mentioned above.4. Accountability4.1 Accountability means assurance that the results reportedrefer directly to the samples submitted.4.2 Prior to submitting samples to the laboratory, the pro-spective
8、user should consult with laboratory personnel con-cerning his needs and the capability of the laboratory to satisfythem. It is the responsibility of the originator of the samples toselect and identify proper samples for submission to thelaboratory, to decide what information is required (especially,
9、to define the use to be made of the information), and, afterconsulting with laboratory personnel, to submit the samples insuitable containers, properly labeled, and accompanied bywritten instructions identifying the samples, their nature, andthe information sought through chemical analysis. This sho
10、uldbe done formally, using a well-defined document for informa-tion transfer to initiate work in the laboratory.4.3 Laboratory management establishes a written account-ability system to be used throughout the laboratory at all times.This implies traceability and documentation of all reportedresults
11、through the laboratory back to the submitted sample.This system should have the following general characteristics:4.3.1 Each nonroutine job submitted by a user of thelaboratorys services is assigned an internal laboratory identi-fication number (ID), which is used to correlate all samples,work, time
12、 and cost accounting, consultation, and reports andother paperwork associated with that job. The final report thatis returned to the originator will always bear the number (ID)for future reference. Moreover, it is convenient for laboratorydata to be filed according to sequential ID numbers. Forexamp
13、le, “86/0428” might identify the associated work as the428th request submitted in the year 1986. The Data Recordshould provide all data generated during the analyses, names ofpersons performing the analyses, dates the analyses wereperformed, and any unusual occurrences that happened duringthe analys
14、es. Accountability for production control samples isnormally maintained separately from the nonroutine recordsbecause results from production control samples are usuallyreported on routine report forms, the samples being identifiedwith the day, shift, run, or lot from which they were taken.1This gui
15、de is under the jurisdiction of ASTM Committee E01 on AnalyticalChemistry for Metals, Ores, and Related Materials and is the direct responsibility ofSubcommittee E01.22 on Statistics and Quality Control.Current edition approved Oct. 1, 2003. Published November 2003. Originallyapproved in 1982. Last
16、previous edition approved in 1998 as E 882 98.2ASTM Manual Series, ASTM, 6th Edition, 1990.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, U
17、nited States.4.3.2 Each sample, specimen, sample site, or other uniquepiece of material or container identified as a separate sample bythe originator should be assigned a sequential item number(NN) for internal laboratory use. As soon as the samples areaccepted by the laboratory, laboratory personne
18、l will markeach sample or sample container with its own laboratorysample number (ID-NN) in such manner that the label is notlikely to become separated from its sample or renderedunreadable during its residence in the laboratory. For example,the fifth sample on the above-mentioned request might beide
19、ntified as “86/0428-05.”4.3.3 All laboratory work records, intermediate samplecontainers, data, and reports for a specific sample will beidentified by the same laboratory identification and itemnumber to avoid any opportunity for samples or data to be lostor intermixed within or between jobs.4.3.4 T
20、he first and last steps in the accountability procedureare functions of technical supervision. Before any work isperformed, the compatibility of the work requested with thephysical condition of the samples and the capabilities of thelaboratory must be verified. When the analysts have completedtheir
21、work, the results must be reviewed to be certain that allinformation requested has been determined and that the workhas been performed with the required care and precision. Inthis latter regard, quality control procedures prove invaluableboth to the analysts performing the work and the reviewingsupe
22、rvisor. The supervisor also verifies that the results arecalculated in units that are most meaningful to the submitterand that the units and basis on which the results are calculatedare clearly stated.4.3.5 Except for the most routine work, the original ana-lysts data book, a serial listing of labor
23、atory identificationnumbers and descriptions, and a copy of each job report sheetare retained in the laboratorys records for the periods of timeestablished by laboratory policy. Intermediate calculations andsamples are normally discarded after the submitter has had areasonable opportunity to submit
24、questions concerning theresults and request return of his samples. In some cases,customer specifications may dictate the records that must beretained and the retention times for both analytical records andlaboratory samples.5. Quality Control5.1 Quality control of analytical methods provides theinfo
25、rmation needed to ensure that procedures, equipment, andpersonnel are performing at the levels of precision and accu-racy required by the intended use of the data.5.2 General CharacteristicsThe following factors havebeen found helpful in maximizing the effectiveness and mini-mizing the cost of quali
26、ty control procedures:5.2.1 Involve the operators or analysts who actually performthe work to the greatest possible extent.5.2.2 Use the simplest, most direct statistical proceduresthat will provide the necessary degree of control. This meansthat graphical or simplified arithmetic procedures are pre
27、ferred.5.2.3 Perform the quality control measurements as early inthe measurement process as possible. This prevents waste ofanalytical effort if the method is not initially in control.However, when a prolonged series of measurements is made, itis also necessary to verify that the method remains in c
28、ontrolthroughout the run.5.2.4 Provide specific action limits and describe exactlywhat must be done when these limits are exceeded.5.2.5 For each method (for each sample type), choose acontrol material that is known to be stable and homogeneousand has measured values within the range of interest. An
29、yinhomogeneity in the control sample will add to the variance ofthe results. Any increase in variability that is not related to themeasurement process will reduce the sensitivity of the qualitycontrol procedure to detect changes in the measurementprocess. Where possible, the control material should
30、be similarto the samples to be analyzed. Obtain as large an amount ofcontrol material as can be prepared in a homogeneous statebecause considerable effort is required to prepare a newcontrol. Always prepare a new control material well in advanceof exhausting the old one so that the new chart is read
31、y whenneeded. In situations where satisfactory control material cannotbe obtained, alternative techniques (such as, retest by a senioranalyst) may be substituted for the control chart approach.5.2.6 Give analysts specific instructions concerning theirresponse to an out-of-control condition. Supervis
32、ion maydecide that, if the analyst can correct the problem so that thecontrol sample results again plot within limits, the process maycontinue without immediate contact with the supervisor. Inother situations, the supervisor may need to become involvedwith each out-of-control incident. In either cas
33、e, adjustments tothe process should be recorded to explain each shift in thecontrol measurements.5.2.7 Provide for a periodic in-depth review by supervisionand management of the overall effectiveness of the laboratoryquality control system. Operating experience may indicate thatmethods should be add
34、ed to, or dropped from the program, thatthe frequency of specific control samples should be increasedor decreased, or that a different strategy might be moreappropriate for control of a specific method. The interval forsuch reviews should be determined by the uniformity of theprocesses that generate
35、 the samples. Any anticipated or ob-served change in the character of the samples being analyzedshould initiate at least a cursory review of the control proce-dures for the methods that apply to those samples.5.3 Laboratory Quality Control StrategiesControl chartmethods are suitable for laboratory q
36、uality control programs.The choice of which control strategy to use depends oncircumstances: the type of instrument or laboratory procedure,the number of samples and frequency of the analyses, and thecloseness of control required. The following are appropriate:5.3.1 The X- and R-chart method is most
37、 frequently used.The control sample is run two or more times during the run,batch, or shift. The average is plotted on the X-chart and theabsolute value of the difference between the high and lowvalues, the range, is plotted on the R-chart. If the average fallsbetween the upper and lower control lim
38、its and the range fallsbelow the upper control limit, the process is considered to be incontrol. Fig. 1 shows the essential features of charts foraverages and ranges.E 882 87 (2003)25.3.2 The X-chart method (often called the control chart forindividuals) is useful for measurements that are made on a
39、frequent or continual basis. It is appropriate for methods orinstruments for which the usual mode of failure producesrelatively large shifts in results and the cost of a determinationprecludes performing replicate analyses of control samples. Itsmain characteristic is that it responds rapidly to sud
40、denrelatively large changes in the analytical process, but it is notas sensitive to small changes as the X- and R-chart method.Each time the control material is analyzed, its value is plottedon the X-chart. If the point plots between the upper and lowercontrol limits, the analytical process is consi
41、dered to be incontrol. Fig. 3 shows the essential features of charts forindividuals.5.3.3 A combination of the above two methods constitutes auseful strategy. A fixed number of control sample runs aremade during a period that samples are being analyzed (suchperiod could, for example, be a shift or a
42、 day in a continuousanalysis process). Each individual value is plotted on theX-chart as the measurement is completed. Their average valueand range are plotted on the X- and R-charts. The additionaleffort to prepare and maintain both types of control charts maybe justified in situations where errone
43、ous assays would causelarge economic losses. Other control chart techniques that maybe appropriate for special circumstances may be found in theANSI/ASQC document.5.3.4 Comparison with standard reference materials (SRMs)is frequently the only strategy that can be employed forFIG. 1 Control Chart for
44、 AveragesFIG. 2 Control Chart for RangesE 882 87 (2003)3infrequently used analytical methods or for nonroutine sampletypes. If an SRM such as one from the National Institute ofStandards and Technology (similar to the samples) is run alongwith the samples, comparison of the measured value againstthe
45、known value of the standard provides a measure ofconfidence in the sample assays. Lacking an SRM, anypreviously analyzed material may be used. In all cases, it isimportant to retain as large a portion of such a material aspossible and to tabulate the results, the method used, the date,and the analys
46、t. Materials and data thus obtained may haveimportant future statistical or control chart use.5.4 Definitions:5.4.1 mean:X5 X11 X21 . . Xn!/n! (1)where n = the number of analytical values.5.4.2 grand mean:X5 X11 X21 . . Xk!/k! (2)where K = the number of individual means.5.4.3 range:R 5 Xh2 Xl(3)wher
47、e:Xh= highest observed value, andXl= lowest observed value in the data being averaged.5.4.4 average range:R5 R11 R21 . Rk!/k! (4)5.4.5 estimated standard deviation:s 5(Xi2 X!2n 1(5)where:xi= the value of the n successive observations, and( = the sum of the squares of the indicated differences.5.5 Co
48、ntrol Chart ConstructionCalculate the centralvalue and control limits. Prepare the control chart with thevertical scale labeled so that the central value is approximatelymidway on the graph. Select a scale factor to permit the resultsto be plotted accurately and easily. The horizontal axis islabeled
49、 by shift, day, run number, or run date, as appropriate.Draw and label the central line and the lines representing theupper and lower control limits. The central line may be thegrand average of the values obtained during the base perioddescribed below, or it may be a specifed value based uponexperience. Title the chart with the method, the control sampleidentification, and any special instructions. Show all of theoriginal data points that were used to calculate the controllimits.5.5.1 X- and R-ChartAt least two independent measure-ments must be made on th
