Page:NIOSH Manual of Analytical Methods - 3800.pdf/41

ORGANIC AND INORGANIC GASES by FTIR Spectrometry: METHOD 3800, Issue 1, dated 15 March 2003 - Page 41 of 47

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Table E3. Parameters Used to Generate Synthetic Sample Spectra Containing TFE, DFE, and Water.

TFE Scaling Factor	TFE Synthetic Conc. (ppm)	DFE Scaling Factor	DFE Synthetic Conc. (ppm)	H2O Scaling Factor	Synthetic Sample Spectrum File Name
0	0	0	0	0.6	S001.spc
0	0	0	0	1.2	S002.spc
1.200	25.0	1.264	25.0	0.6	S551.spc
1.200	25.0	0.253	5.00	0.6	S511.spc
0.240	5.00	1.264	25.0	0.6	S151.spc
1.200	25.0	1.264	25.0	1.2	S552.spc
1.200	25.0	0.253	5.00	1.2	S512.spc
0.240	5.00	1.264	25.0	1.2	S152.spc

A spectrum representing random absorbance noise was added to each synthetic spectrum. The noise spectrum was generated using the function RANDOM within the program GRAMS/32 V4.1 1 (Galactic, Inc.; see the Array Basic User’s Guide, V4.1, page 31 6); similar functions are also available in Microsoft Excel. For the noise spectrum, the root mean square absorbance noise N_RMS (see also equation C2, which defines the RSA), calculated over the appropriate analytical region(s) according to

$N_{\text{RMS}}={\sqrt {\sum _{l=p}^{l=q}{\frac {(R_{l})^{2}}{q-p}}}}$⁠Equation E2

was 0.00034 in the region 1438 to 1282 cm^-1; this is very close to the value obtained from actual absorbance spectra (provided by MID AC Corporation) recorded with the quoted system configuration in the region 1005 to 932 cm^-1.

The synthetic spectra represent four different mixtures of TFE and DFE (including one "mixture" which contains neither compound), each at two different moisture levels.

Table E4 lists the results of a LSF analysis (program 4FTIMD V15, Rho Squared; see Reference 18) for TFE, DFE, and water in the analytical region 1215 to 1080 cm^-1 using the reference spectral files TFE3.spc (CCP = 133 .2 ppm-m) and dfeav04.spc (CCP = 133.3 ppm-m), and wat01bl.spc. Note that these are not the same reference spectra which were used in the generation of the synthetic sample spectra, and that the results for water are in arbitrary units. The analysis included the determination of two baseline correction parameters along with the compound concentrations.

NIOSH Manual of Analytical Methods, Fourth Edition