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linear calibration model or a linear model not through the origin has been employed forthe initial calibration, consult Sec. 7 of Method 8000 for the specifics of calibrationverification.% Difference ' CF & CF vCF× 1007.5.2.2 If this criterion is exceeded for any analyte, use the approach describedin Sec. 7 of Method 8000 to calculate the average percent difference across all analytes.If the average of the responses for all analytes is within ±15%, then the calibration hasbeen verified. However, the conditions in Sec. 7 of Method 8000 also apply, e.g., theaverage must include all analytes in the calibration, regardless of whether they are targetanalytes for a specific project, and the data user must be provided with the calibrationverification data or a list of those analytes that exceeded the ±15% limit.7.5.2.3 If the calibration does not meet the ±15% limit (either on the basis ofeach compound or the average across all compounds), check the instrument operatingconditions, and if necessary, restore them to the original settings, and inject anotheraliquot of the calibration verification standard. If the response for the analyte is still notwithin ±15%, then a new initial calibration must be prepared. The effects of a failingcalibration verification standard on sample results are discussed in Sec. 7.5.7.7.5.3 Compare the retention time of each analyte in the calibration standard with theabsolute retention time windows established in Sec. 7.4.6. As described in Method 8000, thecenter of the absolute retention time window for each analyte is its retention time in the midconcentrationstandard analyzed during the initial calibration. Each analyte in each standardmust fall within its respective retention time window. If not, the gas chromatographic systemmust either be adjusted so that a second analysis of the standard does result in all analytesfalling within their retention time windows, or a new initial calibration must be performed andnew retention time windows established.7.5.4 Inject a 2-µL aliquot of the concentrated sample extract. Record the volumeinjected to the nearest 0.05 µL and the resulting peak size in area units.7.5.5 Tentative identification of an analyte occurs when a peak from a sample extractfalls within the absolute retention time window. Each tentative identification must be confirmedusing either a second GC column of dissimilar stationary phase or using another techniquesuch as GC/MS (see Sec. 7.7).When results are confirmed using a second GC column of dissimilar stationary phase,the analyst should check the agreement between the quantitative results on both columns oncethe identification has been confirmed. See Sec. 7 of Method 8000 for a discussion of such acomparison. Unless otherwise specified in an approved project plan, the higher result shouldbe reported, as this is a conservative approach relative to protection of the environment. If therelative percent difference of the results exceeds 40%, consult Method 8000 for steps that maybe taken to address the discrepancy.7.5.6 When using the external calibration procedure (Method 8000), determine thequantity of each component peak in the sample chromatogram which corresponds to thecompounds used for calibration purposes, as follows. Proper quantitation requires theappropriate selection of a baseline from which the peak area or height can be determined.CD-ROM 8081A - 14 Revision 1December 1996
7.5.6.1 For aqueous samplesConcentration (µg/L) '(A x )(V t )(D)(CF)(V i)(V s)where:AVxtD––CFVVis= Area (or height) of the peak for the analyte in the sample.= Total volume of the concentrated extract (µL).= Dilution factor, if the sample or extract was diluted prior to analysis. If no dilutionwas made, D = 1. The dilution factor is always dimensionless.= Mean calibration factor from the initial calibration (area/ng).= Volume of the extract injected (µL). The injection volume for samples andcalibration standards must be the same. For purge-and-trap analysis, V i is notapplicable and therefore is set at 1.= Volume of the aqueous sample extracted in mL. If units of liters are used for thisterm, multiply the results by 1000.Using the units specified here for these terms will result in a concentration in units ofng/mL, which is equivalent to µg/L.7.5.6.2 For non-aqueous samplesConcentration (µg/kg) '(A x )(V t )(D)(CF)(V i)(W s)––where A , V , D, CF, and V are the same as for aqueous samples, andx tiW = Weight of sample extracted (g). The wet weight or dry weight may be used,sdepending upon the specific application of the data. If units of kilograms areused for this term, multiply the results by 1000.Using the units specified here for these terms will result in a concentration in units ofng/g, which is equivalent to µg/kg.7.5.6.3 See Method 8000 for the equation used for internal standardquantitation.7.5.6.4 If the responses exceed the calibration range of the system, dilute theextract and reanalyze. Peak height measurements are recommended over peak areaintegration when overlapping peaks cause errors in area integration.7.5.6.5 If partially overlapping or coeluting peaks are found, change GCcolumns or try GC/MS quantitation (see Sec. 8.0 and Method 8270).CD-ROM 8081A - 15 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: mean CF ' CF 'nj CF ii'1nwhere n is
Page 17 and 18: 7.5.11 Identification of mixtures (
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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