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ORGANIC AND INORGANIC GASES by FTIR Spectrometry: METHOD 3800, Issue 1, dated 15 March 2003 - Page 40 of 47 Figure E.6 TFE and DFE Spectra for Absorbance Area Calculations

E2.

Presented in this section is a description of a least squares fit (LSF) analysis for the two compounds TFE and DFE in ambient air samples. As is always the case before actual measurements are taken, no actual sample data for mixtures of the compounds in the assumed matrix (ambient air) were available as these analyses were performed. Accordingly, the following description is based on synthetic spectra generated from available reference spectra for TFE, DFE, and water.

In order to not overestimate the effectiveness of the FTIR technique, the noise levels in the synthetic sample spectra were artificially raised, and the reference spectra used are not those most likely to provide an optimal analysis. This is the most prudent course available to an analyst attempting to predict the performance of the FTIR method under essentially unknown conditions, and it is the course recommended by the authors to analysts who find themselves in this common situation.

Estimates of the LOD for this sample matrix (see Appendix E, Section 1) indicate that the analytical region from 1215 to 1080 cm$-1$ will likely provide the most reliable TFE and DFE concentrations. The system configuration parameters used in those estimates are assumed to hold in the following description.

E2A. Generation and Analysis of Synthetic Sample Spectra of TFE and DFE

Table E3 describes the mathematical generation of synthetic samples for the following LSF analysis description. Each sample spectrum consists of the sum of scaled reference spectra for TFE (tfe4.spc, CCP = 208.3 ppm-m), DFE (dfeav05.spc, CCP = 197.8 ppm-m) and water (wat02bl.spc). The scaling factors indicated in Table E3 were used to generate synthetic sample spectra at the listed concentrations and the assumed absorption pathlength of 10.0 meters. NIOSH Manual of Analytical Methods, Fourth Edition