تسجيل الدخول

تسجيل

Instrument calibration , Wavelength (wavenumber) scale

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  p429-430

2026-11-12

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Instrument calibration

Wavelength (wavenumber) scale

The wavelength (wavenumber) scale is a critical parameter in infrared, particularly where computer matching of spectra is employed for identification purposes. As noted in discussions later in this chapter, computer matching relies on comparison of the major absorbance bands in the IR spectrum. The data system calculates the wavenumbers corresponding to the main absorbance bands for the sample and then, in effect, compares these with the wavenumbers for the main absorbance bands in the reference library spectra. If the wavenumbers are not accurate for the sample spectrum, the data system will not produce a correct library match. A card carrying an accredited transparent film of polystyrene (0.035 mm in thickness) is used to calibrate the wavelength (wavenumber) scale. The spectrum should have the form illustrated in Figs 2 and 1. Peak locations and tolerances recommended in the British Pharmacopoeia (British Pharmacopoeia Commission 2007) are given in the inset in Fig. 1.

Figure 1 Zoomed-in regions of the IR spectrum of a 40 μm thick polystyrene film indicating the location of critical parameters. A whole spectrum is illustrated in Fig. 16.2.

Figure 2 Liquid sample or Nujol mull sandwiched between two NaCl plates.