ne samples collected at the 1 ppm PEL could be successfully stored in the 0.1% sulfamic acid collection solution. After sample collection using MFGBs, samples were transferred into 20-mL vials, capped with Teflon-lined caps, and stored at ambient laboratory temperatures in a dark environment for 1, 5, 15, or 30 days before analysis. Results: Samples analyzed after 30 days were found to be within 3% of those analyzed immediately. Thus, storage does not represent a source of bias that would need to be corrected in the method. Storage stability data are presented in Table 5. 7. Independent Method (Analytical) An independent volumetric method (9.8.) involving a thiosulfate titration was used to determine the concentration of chlorine used for spiking. Chlorine gas was generated at a theoretical concentration which would give a chlorine concentration of 21.70 g/mL in a specified volume of sulfamic acid. This value was calculated using the equation given in Appendix A. The gas was collected in 0.1% sulfamic acid solution which was then used as a chlorine stock solution for spiked samples (Section 2.). All other samples were taken using the generation system. Analyses of the stock solution were performed using the RCE and the thiosulfate titration methods. The following results were obtained: Method-------------------------------------------------------------------------------- Chlorine (g/mL)-------------------------------------------------------------------------------- Titration 20.45 RCE 20.92 The average value of 20.69 g/ml from both methods was used as the stock solution concentration for the spiked samples mentioned in Section 2. 8. Conclusions This sampling and analytical method has been shown to be precise and accurate at exposures near the OSHA PEL of 1 ppm when using 15-L air volumes. Breakthrough or storage stability do not pose significant problems under the conditions tested. The development and evaluation of this method took ...
