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 SULFUR HEXAFLUORIDE by portable GC: METHOD 5512, Issue 2, dated 15 August 1994 - Page 5 of 4 Packed column, ambient temperature isothermal gas chromatography provides rapid analysis of samples with little sample preparation, but at the expense of providing limited separation of the analyte of interest from potential interferences. The column used in the evaluation of this method was 38 cm x 0.6-cm (OD) stainless steel, packed with 100-120 mesh activated aluminum oxide, using an Argon carrier gas flow of approximately 30 mL/min. These conditions provided a retention time of approximately 1.4 minutes for SF 6, allowing replicate analyses of multiple samples and calibration standards during a work shift. Increasing the carrier gas flow provided a somewhat faster analysis, but resulted in a loss of sensitivity. Decreasing the carrier gas flow lengthened the retention time, but did not result in an increase in sensitivity. Baseline drift was typically less than 10% per hour. Relative standard deviations for replicate analyses ranged from 0.90 to 5.64%, with a mean of 2.2%. Analysis of certified commercial standards ranged from 97.6 to 102.8%, with a mean of 99.6%. Samples in multi-layer 5.5-mil bags (Calibrated Instruments, Inc.) showed no detectable change in concentration over a 28-hr period. Samples in 4 mil Tedlar bags (SKC, Inc.) showed no detectable change in concentration after 28 hrs.

REFERENCES: [1] NIOSH Manual of Analytical Methods, 2nd ed., Vol. 5, U.S. Department of Health, Education, and Welfare (NIOSH) Publ. 79-141 (1979).

METHOD WRITTEN BY: G.E. Burroughs, NIOSH/DPSE.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94