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7 Quality Control <br />7.1 Quality control procedures are followed in two areas: <br />sampling and analysis. <br />7.2 The quality control procedures used in sampling are: <br />7.2.1 The Tedlar bag samplers are checked every 6 months for <br />leakage and contamination. The interval is shortened <br />if any malfunction is suspected. A written record is <br />maintained of the history of each sampler. (See <br />Appendix A). <br />7.2.2 The Tedlar bags are checked for leakage and contamin- <br />ation before being used for sampling. A log book is <br />maintained with a complete history of bag usage. <br />(See Appendix B). <br />7.3 The quality control procedures used in analyzing the sample <br />are: <br />7.3.1 The accuracy of the method has not been determined. <br />7.3.1.1 Every six to nine months a calibration standard is prepared <br />in a glass -lined Pfaudler Chamber maintained by the Environ- <br />mental Laboratory Section of the Haagen -Smit Laboratory. <br />7.3.1.2 The chamber is repeatedly evacuated and flushed with zero <br />air until it is shown by gas chromatographic analysis to <br />be free of any significant contamination. <br />7.3.1.3 To prepare the standard, the chamber is re -evacuated and <br />filled with zero air to a pressure of 5 psia. <br />7.3.1.4 A measured volume of a volumetrically prepared solution <br />of halogenated hydrocarbons in methanol is injected via <br />a heated injector into a stream of zero air as it is <br />flowing into the chamber. The volume of the solution <br />injected into the chamber is chosen so as to give the <br />desired gas phase concentration of halogenated hydro- <br />carbons when the chamber is pressurized to 16 psia with <br />zero air. <br />7.3.2 Calibration standards are prepared periodically. The <br />accuracy of the standard is verified and the pro- <br />cedure validated by comparing the concentration of <br />tetrachloroethane in the chamber to that of an NBS <br />standard. <br />7.3.2.1 A newly prepared chamber working standard is rejected <br />unless the tetrachloroethene concentration based on <br />calculation agrees within +/- 5% of the value <br />determined by analysis, using the NBS standard for <br />calibration. <br />0 <br />