fused aromatic systems, cf. biphenyl and fluorene (Figure 9.11(b)). Structures containing heteroatoms or
which are ionized may undergo rapid relaxation by intersystem crossing thereby reducing or inhibiting
fluorescence, e.g. pyridine, nitrobenzene and iodobenzene exhibit no fluorescence whereas aniline,
phenol and chlorobenzene all fluoresce.
Some examples of fluorescing species and their analytical uses are included in Table 9.5.
Table 9.5 Applications of quantitative visible and ultraviolet spectrometry
Element or compound determined Reagent Example of application
Absorptiometry
Fe o-phenanthroline natural waters, petroleum products
Cu neocuproine minerals, alloys
Mn oxidation to steels
Cr diphenylcarbazide alloys, minerals
Hg, Pb dithizone food products, fish
reduction to molybdenum blue fertilizer residues, soils
aspirin — analgesic preparations
cholesterol Liebermann–Burchard reaction body fluids
sulphonamides diazo derivatives drug preparations
DDT nitrated derivative soils, fish
Element or compound determined Fluorescent emission maximum
(nm)
Example of application
Fluorimetry
vitamin A 500 nm foodstuffs, vitamin tablets
LSD > 430 nm body fluids
amphetamine codeine, morphine
drug preparations and body fluids
PAH 320 – 550 nm environmental samples
amines and amino acids as
derivatized by ninhydrin, o-
phthaldehyde (OPA), dansyl
chloride or fluorescamine
440 – 550 nm pre-^ or post-column derivatization for HPLC
separations
Al as alizarin garnet red complex 580 nm water samples and soils
Cd as 2-(o-hydroxyphenyl) –
benzoxazole complex
— water samples and soils
B as benzoin complex 450 nm water samples and soils