Flow-rate dependence of post-column reaction chromatographic detectors and optimization of reactor length for slow chemical reactions

Spectrofluorimetric determination of formaldehyde by a flow-injection method based on its catalytic effect on the acridine yellow-bromate reaction

A flow-injection configuration for the determination of formaldehyde is proposed. The method is based on the enhancing effect of formaldehyde on the oxidation of acridine yellow by bromate in acidic medium. The proposed procedure is simple, inexpensive, sensitive and suitable for concentrations of formaldehyde between 1 and 56 microg mL(-1). A sampling-rate of 60 samples h(-1) was achieved. The effect of several organic and inorganic species was studied. The method was applied to the determination of formaldehyde in pharmaceuticals, milk and air in work environments. The accuracy of the method was confirmed by comparing the results with those obtained using the standard acetylacetone method.

Theoretical concepts of on-line liquid chromatographic-biochemical detection systems. II. Detection systems based on labelled affinity proteins

A theoretical concept for on-line liquid chromatography-biochemical detection (LC-BCD) using labelled affinity proteins as reporter molecules is presented. The BCD system is based on the post-column addition of labelled affinity proteins such as fluorescein-labelled streptavidin to the LC effluent. After a short reaction time, free and analyte-bound label are separated during passage through a column packed with an immobilised-ligand support. The bound fraction passes the column unretained and is measured downstream by means of a conventional HPLC detector. The theoretical model presented here relates the detector response to the most important instrumental and biochemical parameters such as dispersion, reaction time, concentration and affinity of the affinity protein and the number of binding sites. The theoretical concept is validated using fluorescein-labelled streptavidin and biotin as model system.

Theoretical concepts of on-line liquid chromatographic-biochemical detection systems. I. Detection systems based on labelled ligands

A theoretical foundation for on-line coupling of liquid chromatography (LC) with fluororeceptor assays based on fluorescent ligands is presented. Using a recently developed LC-receptor affinity detection (RAD) system as a model, equations are derived which describe the detector response and the signal-to-noise ratio as a function of important biochemical and instrumental parameters. The effect of ligand and label affinity, and receptor concentrations on the detector performance were investigated. It was found that the response of the RAD system is correlated with the affinity of the injected compounds and that the relative affinity order of binding ligands is maintained in the RAD system.

Liquid chromatographic separation and stereoselective detection of L- and D-amino acids with catalytic reaction detection using immobilized enzymes

A post-column LC detection system is described for the stereoselective detection of L- and D-amino acids. The effluent of the LC column passes an immobilized enzyme reactor (IMER) containing either L- or D-amino acid oxidase. The hydrogen peroxide formed in this reactor by the oxidation of the amino acids is then transported to a second IMER containing horse-radish peroxidase. With the addition of 4-aminophenazone and dichlorophenosulphonyl chloride to the carrier, the hydrogen peroxide is reacted to form a red-coloured complex which is detected in a flow-through photometric cell at 514 nm. Applications to the analysis of amino acids in bovine and human sera are described.

High-performance liquid chromatographic separation of some mono- and disaccharides with detection by a post-column enzyme reactor and a chemically modified electrode

The effluent from a chromatographic column was mixed with nicotinamide adenine dinucleotide coenzyme (NAD+) buffer and passed through a packed-bed reactor containing immobilized glucose dehydrogenase. Oxidation of the carbohydrates emerging from the column produced an equivalent amount of reduced coenzyme (NADH), which was detected electrochemically using an electrode modified with 7-dimethylamino-1,2-benzophenoxazine (Meldola Blue). Separation was effected in three different chromatographic systems containing a protonated ion exchanger, a calcium(II)-saturated or a lead(II)-saturated ligand exchange column. Separation, detection and k' values are reported for glucose, 2-deoxyglucose, xylose, mannose, cellobiose, lactose, ribose and glucosamine. The detection limit was 2 ng for a 20-microliter injection of glucose and the response was linear up to 6300 ng. Samples from fermentation of penicillin were analysed for lactose and glucose with the described detector. A comparison with the recordings from a refractive index detector showed that the selectivity of the enzymes and the modified electrodes are necessary for the determination of glucose and lactose.