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7.5.7 Each sample analysis must be bracketed with an acceptable initial calibration,calibration verification standard(s) (each 12-hour analytical shift), or calibration standardsinterspersed within the samples.Although analysis of a single mid-concentration standard (standard mixture or multicomponentanalyte) will satisfy the minimum requirements, analysts are urged to use differentcalibration verification standards during organochlorine pesticide analyses. Also, multi-levelstandards (mixtures or multi-component analytes) are highly recommended to ensure that thedetector response remains stable for all the analytes over the calibration range.The results from these bracketing standards must meet the calibration verification criteriain Sec. 7.5.2. When a calibration verification standard fails to meet the QC criteria, all samplesthat were injected after the last standard that last met the QC criteria must be evaluated toprevent mis-quantitations and possible false negative results, and re-injection of the sampleextracts may be required. More frequent analyses of standards will minimize the number ofsample extracts that would have to be reinjected if the QC limits are violated for the standardanalysis.However, if the standard analyzed after a group of samples exhibits a response for ananalyte that is above the acceptance limit, i.e., >15%, and the analyte was not detected in thespecific samples analyzed during the analytical shift, then the extracts for those samples donot need to be reanalyzed, as the verification standard has demonstrated that the analytewould have been detected were it present. In contrast, if an analyte above the QC limits wasdetected in a sample extract, then re-injection is necessary to ensure accurate quantitation.If an analyte was not detected in the sample and the standard response is more than 15%below the initial calibration response, then re-injection is necessary to ensure that the detectorresponse has not deteriorated to the point that the analyte would not have been detected eventhough it was present (i.e., a false negative result).7.5.8 Sample injections may continue for as long as the calibration verificationstandards and standards interspersed with the samples meet instrument QC requirements.It is recommended that standards be analyzed after every 10 samples (required after every 20samples and at the end of a set) to minimize the number of samples that must be re-injectedwhen the standards fail the QC limits. The sequence ends when the set of samples has beeninjected or when qualitative and/or quantitative QC criteria are exceeded.7.5.9 If the peak response is less than 2.5 times the baseline noise level, the validityof the quantitative result may be questionable. The analyst should consult with the source ofthe sample to determine whether further concentration of the sample is warranted.7.5.10 Validation of GC system qualitative performance7.5.10.1 Use the calibration standards analyzed during the sequence to evaluateretention time stability. The retention time windows are established using the absoluteretention time of each analyte as described in Method 8000.7.5.10.2 Each subsequent injection of a standard during the 12-hour analyticalshift (i.e., those standards injected every 20 samples, or more frequently) must bechecked against the retention time windows. If any of these subsequent standards falloutside their absolute retention time windows, the GC system is out of control.Determine the cause of the problem and correct it. If the problem cannot be corrected,a new initial calibration must be performed.CD-ROM 8081A - 16 Revision 1December 1996
7.5.11 Identification of mixtures (i.e. Chlordane and Toxaphene) is based on thecharacteristic "fingerprint" retention time and shape of the indicator peak(s); and quantitationis based on the area under the characteristic peaks as compared to the area under thecorresponding calibration peak(s) of the same retention time and shape generated using eitherinternal or external calibration procedures.7.5.12 If compound identification or quantitation is precluded due to interference (e.g.,broad, rounded peaks or ill-defined baselines are present) cleanup of the extract orreplacement of the capillary column or detector is warranted. Rerun the sample on anotherinstrument to determine if the problem results from analytical hardware or the sample matrix.Refer to Method 3600 for the procedures to be followed in sample cleanup.7.6 Quantitation of multi-component analytes - Multi-component analytes present problemsin measurement. Suggestions are offered in the following sections for handing Toxaphene,Strobane, Chlordane, BHC, and DDT.7.6.1 Toxaphene and Strobane - Toxaphene is manufactured by the chlorination ofcamphenes, whereas Strobane results from the chlorination of a mixture of camphenes andpinenes. Quantitation of Toxaphene or Strobane is difficult, but reasonable accuracy can beobtained. To calculate Toxaphene from GC/ECD results:7.6.1.1. Adjust the sample size so that the major Toxaphene peaks are 10-70%of full-scale deflection (FSD).7.6.1.2 Inject a Toxaphene standard that is estimated to be within ± 10 ng ofthe sample amount.7.6.1.3 Quantitate Toxaphene using the total area of the Toxaphene pattern orusing 4 to 6 major peaks.7.6.1.3.1 While Toxaphene contains a large number of compoundsthat will produce well resolved peaks in a GC/ECD chromatogram, it alsocontains many other components that are not chromatographically resolved. Thisunresolved complex mixture results in the "hump" in the chromatogram that ischaracteristic of this mixture. Although the resolved peaks are important for theidentification of the mixture, the area of the unresolved complex mixturecontributes a significant portion of the area of the total response.7.6.1.3.2 To measure total area, construct the baseline ofToxaphene in the sample chromatogram between the retention times of the firstand last eluting Toxaphene components in the standard. In order to use the totalarea approach, the pattern in the sample chromatogram must be compared tothat of the standard to ensure that all of the major components in the standardare present in the sample. Otherwise, the sample concentration may besignificantly underestimated.7.6.1.3.3 Toxaphene may also be quantitated on the basis of 4 to6 major peaks. A collaborative study of a series of Toxaphene residuesevaluated several approaches to quantitation of this compound, including the useof the total area of the peaks in the Toxaphene chromatogram and the use of asubset of 4 to 6 peaks. That study indicated that the use of 4 to 6 peaks providesCD-ROM 8081A - 17 Revision 1December 1996
Page 1 and 2: METHOD 8081AORGANOCHLORINE PESTICID
Page 3 and 4: CompoundCAS Registry No.Chloropropy
Page 6 and 7: confirmation techniques may be empl
Page 9 and 10: 5.7.2 1-bromo-2-nitrobenzene is sug
Page 11 and 12: columns. Table 2 lists average rete
Page 13 and 14: mean CF ' CF 'nj CF ii'1nwhere n is
Page 15: 7.5.6.1 For aqueous samplesConcentr
Page 19 and 20: Construct a similar baseline in the
Page 21 and 22: 8.0 QUALITY CONTROL8.1 Refer to Cha
Page 23 and 24: 8000, Sec. 8.0 for information on e
Page 25 and 26: TABLE 1GAS CHROMATOGRAPHIC RETENTIO
Page 27 and 28: TABLE 3aFACTORS FOR DETERMINATION O
Page 29 and 30: TABLE 5GC OPERATING CONDITIONS FOR
Page 31 and 32: TABLE 6 (continued)RETENTION TIMES
Page 33 and 34: TABLE 8GC OPERATING CONDITIONS FOR
Page 35 and 36: TABLE 10ANALYTE RECOVERY FROM DICHL
Page 37 and 38: TABLE 12SINGLE LABORATORY ACCURACY
Page 39 and 40: FIGURE 2GAS CHROMATOGRAM OF INDIVID
Page 41 and 42: FIGURE 4GAS CHROMATOGRAM OF TOXAPHE
Page 43 and 44: FIGURE 6GAS CHROMATOGRAM OF ORGANOC

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