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8 / ORGANIC ANALYTICAL METHODS - GC <br />If the RF value over the working range is a constant (less than <br />10% relative standard deviation), the RF can_ be assumed to be <br />invariant and the average RF can be used for calculations. Alter- <br />natively, the results can be used to plot a calibration curve of <br />response ratios, As/Ais against RF. <br />7.2.3.4 The working calibration curve or RF must be verified <br />on each working day by measuring one or more calibration standards. <br />If the response for any parameter varies from the predicted response <br />by more than +10%, either the test must be repeated using a fresh <br />calibration standard, or a new calibration curve must be prepared <br />for that compound. <br />7.3 Gas chromatographic analysis <br />7.3.1 Introduce volatile compounds to the gas chromatograph using <br />direct injection, headspace (Method 5020), or purge -and -trap (Method <br />5030). <br />7.3.2 Table 1 summarizes the estimated retention times and detec- <br />tion limits for a number of organic compounds analyzable using this <br />method. An example of the separation achieved by Column 1 is shown in <br />Figure 1. An example of the separation achieved by Column 2 is shown in <br />Figure 2. <br />7.3.3 Calibrate the system immediately prior to conducting any <br />analysis and recheck for each type of waste. Calibration should be <br />done no less frequently than at the beginning and end of each analysis <br />session. <br />8.0 Quality Control <br />8.1 Before processing any samples, the analyst should demonstrate <br />through the analysis of a distilled water me.hod blank that all glassware <br />and reagents are interference -free. Each time a set of samples is extracted <br />or there is a change in reagents, a method blank should be processed as a <br />safeguard against chronic laboratory contamination. The blank samples should <br />be carried through all stages of the sample preparation and measurement. <br />8.2 Standard quality assurance practices should be used with this <br />method. Field replicates should be collected to validate the precision of <br />the sampling technique. Laboratory replicates should be analyzed to validate <br />the precision of the analysis. Fortified samples should be carried through <br />all stages of sample preparation and measurement; they should be analyzed <br />to va Idate the sensitivity and accuracy of the analysis. If the fortified <br />waste samples do not indicate sufficient sensitivity to detect less than or <br />equal to 1 pg/g of sample, then the sensitivi�y of the instrument should be <br />