Analytical Chemistry

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