Spectrophotometric determination of aliphatic primary and secondary amines by reaction with p-benzoquinone

A simple, sensitive and selective spectrophotometric method has been developed for determination of aliphatic primary and secondary amines. It is based on a reaction with excess of p-benzoquinone in ethanol whereby 1:1 (amine:quinone) coloured products are obtained, which have maximum absorption at 510 nm and E(1cm)(1%) in the range 400-650. The effect of solvent, temperature, concentration of quinone and the presence of water have been kinetically investigated by the initial rate method. The conditions for monitoring amine concentrations as low as 0.1 microg/ml are optimized in the light of the kinetic data. Results with an average recovery of 98.5% and mean standard deviation of 1.9% are obtained with 9 different amines without interference from tertiary amines, ammonia, amides, imides, anilides, hydrazines and alpha-amino-acids.

An air-gap enzyme electrode: development and applications

A novel air-gap enzyme electrode was developed by amalgamating the principles controlling ion-selective electrodes, enzyme kinetics, and diffusion of molecules across membranes. Commercially available ammonia and carbon dioxide gas-sensing electrodes were modified to measure the respective gases over a head-space. A plexiglass cell was designed and fabricated to house the modified electrodes. The air-gap electrodes exhibited superior sensitivity and response characteristics compared to the original membrane electrodes. The plexiglass cell was divided into two compartments by virtue of a selectively permeable membrane. Enzymatic reactions were conducted in the cell to determine quantitatively the concentration of the substrate. L-Phenylalanine ammonia lyase was used to determine L-phenylalanine with the ammonia electrode and L-glutamate decarboxylase was utilized for the determination of L-glutamic acid by the carbon dioxide electrode. Near-Nernstian slopes were obtained for the response of the enzyme electrodes. In addition to the good reproducibility, the method provided unique ability to reuse the same enzyme solution for several determinations of various concentrations of the analyte. The performance of the two compartment cell and air-gap enzyme electrode was found to be superior in comparison to conventional enzyme electrodes.