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<br />7.1.1 Transfer 100 mL of well-mixed sample to a 250-mL Griffin <br />beaker; add 2 mL of 30% H~Oz and sufficient concentrated HNO, to result in <br />an acid concentration of 1% (v/v). Heat for 1 hr at 95°C or until the <br />volume is slightly less than 50 mL. <br />7.1.2 Cool and bring back to 50 mL with Type II water. <br />7.1.3 Pipet 5 mL of this digested solution into a lO~mL volumetric <br />flask, add 1 mL of the 1% nickel nitrate solution, and dilute to 10 mL <br />with Type II water. The sample is now ready for injection into the <br />furnace. <br />7.2 The 196.0 nm wavelength line and a background correction system must <br />be employed. Follow the manufacturer's suggestions for all other spectropho- <br />tometer parameters. <br />7.3 Furnace parameters suggested by the manufacturer should be employed <br />as guidelines. Because temperature-sensing mechanisms and temperature <br />controllers can vary between instruments or with time, the validity of the <br />furnace parameters must be periodically confirmed by systematically altering the <br />furnace parameters while analyzing a standard. In this manner, losses of analyte <br />due to overly high temperature settings or losses in sensitivity due to less than <br />optimum settings can be minimized. Similar verification of furnace parameters <br />may be required for complex sample matrices. <br />7.4 Inject a measured uL aliquot of sample into the furnace and atomize. <br />If the concentration found is greater than the highest standard, the sample <br />should be diluted in the same acid matrix and reanalyzed. The use of multiple <br />injections can improve accuracy and help detect furnace pipetting errors. <br />7.5 Analyze all EP extracts, all samples analyzed as part of a delisting <br />petition, and all samples that suffer from matrix interferences by the method of <br />standard additions. <br />7.6 Run a check standard after approximately every 10 sample injections. <br />Standards are run in part to monitor the life and performance of the graphite <br />tube. Lack of reproducibility or significant change in the signal for the <br />standard indicates that the tube should be replaced. <br />7.7 Duplicates, spiked samples, and check standards should be analyzed <br />every 20 samples. <br />7.8 Calculate metal concentrations: (1) by the method of standard <br />additions, (2) from a calibration curve, or (3) directly from the instrument's <br />concentration read-out. All dilution or concentration factors must be taken into <br />account. <br />7740 - 4 <br />CD-ROM Revision 0 <br />Date September 1986 <br />