Page:NIOSH Manual of Analytical Methods - 3800.pdf/4

 ORGANIC AND INORGANIC GASES by FTIR Spectrometry: METHOD 3800, Issue 1, dated 15 March 2003 - Page 4 of 47 b. W avenumber Reproducibility Check. Record a preliminary workspace air sample spectrum and perform the calculations described in Appendix B, Section 3.

SAMPLING: 9. Using the integration time specified in the test plan, obtain samples and record infrared spectra of the desired ambient gases using the entire sampling system. The sampling location may be changed as desired. For tests of duration greater than 2 hours, or if the FTIR system is moved during sampling, monitor the system ’s single-beam resp ons e level. If changes greater than 5% in non-absorbing regions of the single beam spectrum occur, suspend sampling and record a new background spectrum (see Step 5). Sample spectra must be acquired at each sampling location for a time period no less than the system respon se tim e (se e the system test docu m enta tion). 10. Repeat Step 6; acquire at least one post-test SZ spectrum of N 2 or zero air; confirm the absence of sampling system contaminates. 11. Reco rd at least one post-test CTS spectrum (see Step 7); confirm that the system configuration and the system absorption pathlength (to within 5%) m atch those of the test plan. 12. (Optional) Acquire a pos t-test backgroun d spectrum (see Step 5).

SAMPLE ANALYSIS: 13. Using the analytical regions specified in the test plan, employ an appropriate mathematical analysis (see Ap pendix E) to determ ine preliminary analyte concen trations and their 3F uncertainties from the sam ple spe ctra, re ference spe ctra, a bso rption pathlength, and ga s pre ssu re. NOTE: Reference spectra for all ana lytes m ust m eet or exc eed the Q A/Q C re quirem ents of Appendix D. The reference library must include at least one wavenumber standard spectrum and at least one calibration transfer standard ( CTS) spectrum. The sample absorption due to any analyte may not exceed the m axim um concentration -path length pro duct represente d in the reference library for that compound.

QUALITY CONTRO L: Th e follow ing pro cedu res (Steps 14 throu gh 18 ) may b e perform ed on ly by an exp erienced analyst. 14. Using one of the SZ spectra, calculate the RSA and LOD values (see Appendix E) in the analytical regions pertaining to the test analytes. Verify that the system pathlength, current RSA values, and current LODs are consistent with the test’s data quality objectives. Using a suitable workspa ce air spectrum, perform the W avenumber Reproducibility and Resolution tests described in Appendix B, Sections 3 and 4. If either the W avenumber Reproducibility or Resolution results fail to meet the sp ec ifications, corrective actions are nece ssary (see Step 17 ). 15. Perform qualitative and/or quan titative analyses of the pre- and post-test SZ sp ectra and co nfirm the absence of s am pling syste m conta m inants. If contam inants are found which possess significant absorbance in any analytica l reg ion, co rrective actio ns m ay be necessary (see Step 1 7). Perform qualitative and/or quantitative analyses of the pre- and post-test CTS spectra and confirm that the system absorption pathlength is within 5% of the value quoted in the test plan. 16. Verify that the re ference spe ctra a nd re sults m eet the da ta quality objec tives of the test plan (see Ap pendix D). If they do not, corrective actions may be nece ssa ry (see Step 17). Examine the results of the quantitative sample analysis (Step 13) and verify som e su bse t of them (includ ing tho se w ith rela tively high and relatively low con centrations) m anually to ensure proper operation of analytical program. (Techniques for generating spectra representing the analytes at the concentration indicated by the analysis - “scaled spectra,” as defined in Appendix A— are described in Appendix E. The analyst sh ould gen erate such spectra and compare them, eith er visually or m ath em atic ally, to the indicated sam ple spe ctra.) 17. Corrective actions: If the results of Steps 14 through 16 indicate that the data quality objectives of the test plan have not been achieved, the analyst may perform one or m ore of the following actions: S Averaging of se quential sam ple spectra to reduce the res idual noise area (RSA ). S Inclusion of contaminant reference spectra in the mathem atical analysis.

NIOSH Manual of Analytical Methods, Fourth Edition