SULFITE IN FOOD IS EASY!
Λ ΡΙ ί -lm
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Analyte
CL system
Label
Creatine kinase isoenzymes Bile acids Dansyl chloride
Amino acids
Aliphatic alcohols, aldehydes, ethers, saccharides Cholic acid
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Examples of chemiluminescence (CL) detection with
Polycyclic aromatic amines Co(ll), Cu(ll)
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Table II. HPLC
' 21)PF Sti'irtte(>j kpri(bot
Aminobutyl ethylisoluminol
Ascorbic acid a
Firefly luciferin/ luciferase Bactérieluminescence Trichlorophenyl oxalate/hydrogen peroxide Trichlorophenyl oxalate/hydrogen peroxide Luminol/hydrogen peroxide Luminol/Co(ll)
Hydrogen peroxide/Fe(lll) Lucigenin/base
Detection limit
Reference
350 U/L
14
a
15
low fmol
16
sub pg
17
sub ppb
11
low fig
12
20 fmol
13
5 mg/L
18
not reported
Extr acti< )n)
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omplying with the recent FDA packaged food labeling require ments will be no problem, thanks to voltammetry. Re cent literature references* document and validate the simple procedures used for determining sul fite in food. Give us a call today to find out about this and the many other capabilities of voltammetry. Let us elaborate on the virtues of the technique. MAOAC, VW. 76, No. 1, p. 114; Dev. Food SO., tot. 12, p. 711.
VOLTAMMETRY IT'S FAST... INEXPENSIVE... AND DEPENDABLE.
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tection of bile acids separated by chromatography (15). Bile acids react with nicotinamide adenine dinucleotide (NAD) and 3a-hydroxysteroid-NAD oxidoreductase to generate NADH, which can be detected by coupling with the bacterial bioluminescent reaction: 2 NADH + FMN — 2 NAD + FMNH 2 FMNH 2 + RCHO + 0 2
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light Arisue et al. also evaluated the use of the peroxyoxalate reaction for detection of the fluorescent NADH produced (IS). Although the authors report that sensitivity was not adequate under the conditions used for the clinical assays evaluated, the feasibility of using immobilized enzyme reactors for postcolumn detection was shown. Peroxyoxalate CL is one of the reactions most extensively investigated for postcolumn detection. The attractive feature of this reaction is the ability to detect analytes with native fluorescence (or compounds derivatized with fluorescent labels that are already commercially available) but that are at levels as much as 2-3 orders of magnitude lower than those detected with conventional photoexcitation. Fluctuations and scattering from the light source, which limit detectability, are eliminated in the chemiluminescent measurement. The method was first demonstrated for dansylated amino acids where detection limits in the low femtomole range are achievable by the postcolumn addition of hydrogen peroxide and the
CIRCLE 40 ON READER SERVICE CARD
1254 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 21, NOVEMBER 1, 1987
oxalate ester bis(2,4,6-trichlorophenyl) oxalate (16). Further work has shown that not all fluorophors are efficiently excited by the CL reaction and that therefore an additional degree of selectivity is obtained in complex matrices. Birks et al. detected subpicogram levels of polycyclic aromatic amines in shale and coal oil samples (17). Several reports of peroxyoxalate CL indicate that detectability is limited by a background CL emitted when no fluorophor is added. The lucigenin reaction has been used for the determination of reducing agents and is especially sensitive for ascorbic and dehydroascorbic acids that can be quantitated in the milligram-per-liter range (18). DNA hybridization assays DNA hybridization dot assays are also based on the specificity of a binding process: that of DNA strands for eacb other. An unknown DNA can be identified with the Southern Blot method in which the strands of the analyte are separated and allowed to interact with labeled probe DNA strands on nitrocellulose filter paper. Unbound strands are washed away, leaving only doublestranded DNA on the filter paper. If the label on the probe is detected, the DNA can be identified and, in some cases, quantitated. Again, radioactive tags have been used because of the measurement sensitivity required for quantitation, although these assays often require overnight measurements. Recently, H R P has been used as a DNA probe detected with the luminol
