spectrometry due to their simplicity, freedom from interferences and excellent precision.
Fluorimetry is used much less extensively than absorptiometry because of the limited number of
naturally fluorescing species, although its range of applications can be extended by forming fluorescent
derivatives or complexes of non-fluorescent analytes. Quantitative applications predominate because,
like absorption spectra, fluorescence spectra consist of only a few broad bands. It is inherently more
selective and up to three orders of magnitude more sensitive than absorptiometry, detection limits
extending down to ppb levels. This has made it particularly valuable for the determination of trace
contaminants in foodstuffs and pharmaceuticals and for the determination of fluorescent substances in
clinical and forensic samples. The range of possible analytes includes non-transition metals which form
fluorescent neutral chelate complexes (charged complexes and those of transition metals do not
fluoresce due to rapid relaxation by internal conversion and intersystem crossing), polynuclear aromatic
hydrocarbons (PAH), lysergic acid diethylamide (LSD), penicillin, chlorophyll and other plant
pigments, numerous alkaloids, steroids, some vitamins, amino acids, proteins and enzymes. Some
examples are given in Table 9.5.
9.2—
Infrared Spectrometry
Summary
Principles
Absorption of electromagnetic radiation in the infrared region of the spectrum resulting in changes in
the vibrational energy of molecules.
Instrumentation
Fourier transform spectrometer or double-beam spectrophotometer incorporating prism or grating
monochromator, thermal or photon detector, alkali halide cells.
Applications
Very widespread use, largely for the identification and structural analysis of organic materials; useful
for quantitative analysis but less widely used than UV and visible spectrometry. Near infrared region
used increasingly for industrial quality control.
Disadvantages
Difficult to analyse mixtures. Special cells required for aqueous samples.
Absorption of radiation in the infrared region of the electromagnetic spectrum results in changes in the
vibrational energy of molecules. Energy changes are typically 6 × 103 to 42 × 103 J mol–^1 , which
corresponds to 250–