Page:NIOSH Manual of Analytical Methods - 3800.pdf/15

ORGANIC AND INORGANIC GASES by FTIR Spectrometry: METHOD 3800, Issue 1, dated 15 March 2003 - Page 15 of 47 sample. Estimated in FTIR spectroscopy by forming the ratio of the single-beam sample and background spectra; often presented in %T (100 × T) in spectral representations.

uncertainty—a mathematical quantity determined in a least-squares fitting procedure, used to estimate the likely error in the determination of the sample concentration in a procedure; see Equations C1-C6.

wavelength λ,—the physical distance between successive maxima in the electromagnetic waves which comprise light. The wavelength and speed of light depend on the medium through which the light travels.

wavenumber, w—the reciprocal of the wavelength, also the number of wavelengths of light per unit length, usually expressed in the units cm$-1$. As is true of both the speed and wavelength of light, the wavenumber is dependent on the medium through which the light travels. (See Appendix C, Section 4, and "frequency" in this Appendix.)

wavenumber adjustment—reassignment of the cm$-1$ values associated with single- and/or double beam spectra. Adjustments may be made locally by shifting or stretching the wavenumber scale, or globally stretched by changing the laser wavenumber during the FFT.

White cell—alternate name for a "multi-pass" absorption cell (see above) indicating its inventor.

zero filling—the addition of zero-valued points to the end of a measured interferogram. In most computer programs, specification of a zero filling "factor" of N results in an interferogram with N times as many points as the original interferogram. NIOSH Manual of Analytical Methods, Fourth Edition