Determination of Amino Acids at a Silver Oxide/Silver Phosphate Electrode and the Analysis of Structure‐Response Relationships

Abstract

When a silver electrode is conditioned in a solution of 0.5 M sodium hydroxide with added sodium phosphate and using a dual pulse (500 mV/750 mV vs. Ag/AgCl), a stable silver(I)/silver(II) oxide surface is formed. It has been previously shown that various moieties react with the silver(II) oxide in a chemical oxidation at the outer surface of the oxide layer. This is then followed by re-oxidation of the silver with the generation of current at approximately 500 mV relative to the silver/silver chloride electrode. Previously we found the need to remove carbon dioxide from the base and condition the electrode in a solution containing phosphate ion in order to provide mechanical stability to the oxide layer. We have previously shown this electrode to be applicable to the detection of a variety of carbohydrates. The applicability of the silver oxide/silver phosphate electrode to the post-chromatographic amperometric detection of amino acids was investigated. Calibration studies of amino acids representative of the various classes demonstrated good sensitivity and linearity in the 1 -100 mM range. Responses of amino acids were measured using glucose as an external standard, in order to correct for variability of the oxide layer. Relative responses of the amino acids ranged from 3 down to 0.1. Correlation with structure suggested the importance of absorption in determining the rate of oxidation. Comparison of arginine with n-benzoyl-l-arginine ethyl ester indicated that side chains as well as the backbone amino group can be oxidized. A Levitch plot of alanine was shown to be linear from approximately 30 to 300 radians per second spin rate at a scan rate of 50 mV per second. Application to post-chromatographic detection was demonstrated.

Electrocatalytic oxidation of glucose at gold–silver alloy, silver and gold nanoparticles in an alkaline solution

“…0.35 V extending to the potential limit in the absence of glucose. This oxidation peak is attributed to the oxidation of silver(0) to silver (I) [33]. In the presence of glucose, the catalytic oxidation current was observed at ca.…”

Capacitive Sensing of Amino Acids Using Caliraxene‐Coated Silicon Transducers

“…1,3-(Diethyl-5-oxavaleric Acid)-calix [4]arenecrown-6 (1) and 1,3-(di-4-oxabutanol)-calix [4]arenecrown-5 (2) were synthesized by the procedure described by Duta et al [38]. These macrocycles adopt the 1,3-alternate conformation, which seems to be the most favorable for complexation.…”

“…These macrocycles adopt the 1,3-alternate conformation, which seems to be the most favorable for complexation. Tetraethyl p-tert-butylthiacalix [4]arene tetraacetate (3) was synthesized by the procedure described by Lamartine et al [39]. Tetraethyl p-tertbutylcalix [4]arene tetraacetate (4) was obtained from procedure elaborated by Arnaud-Neu [40] and it adopts the cone conformation in solution.…”

“…Chromatographic separations followed by detection by electrooxidation at high potentials at metallic electrodes have often been carried out. Welch et al have made use of special pulsed coulometry waveforms for detection and in situ cleaning of Au electrodes in the determination of amino acids [3], while DeMott et al have used AgO electrode in order to lower the oxidation potentials [4]. Copper and nickel modified electrodes too have been used in alkaline media to oxidize the amino acids, wherein the reactive species like NiO(OH) and CuO(OH) formed at the electrode surface act as electrocatalysts [5 -7].…”

Enantioselective, potentiometric membrane electrodes based on cyclodextrins for the determination of l-histidine

“…A silver oxide/silver phosphate electrode was proposed for the assay of histidine, but it cannot discriminate between L-and Denantiomers of histidine [22]. This paper reports four enantioselective, potentiometric membrane electrodes (EPMEs) based on α-, β-, 2-hydroxyl-3-trimethylammoniopropyl-β-(as chloride salt) and γ-CDs impregnated on carbon paste for the assay of L-his.…”