Ji-Ye Jin

Integrated pulsed amperometric detection of glufosinate, bialaphos and glyphosate at gold electrodes in anion-exchange chromatography.

A rapid and practical method for direct detection of the herbicides (glufosinate, bialaphos and glyphosate) in anion-exchange chromatography has been developed with integrated pulsed amperometric detection (IPAD). The electrochemical behavior of these herbicides showed catalytic currents based on the oxidation of amines in their structures. Waveform in IPAD was similar to that for amino acids, which exhibited adsorption/desorption catalytic features at gold electrode surface in alkaline solution. Under optimized conditions, detection limits (signal-to-noise ratio of 3) for glufosinate, bialaphos and glyphosate were 20, 65 and 50 ng ml(-1), respectively, with correlation coefficients of 0.995, 0.997 and 0.996 over concentration ranges of 0.1-45, 0.3-32 and 0.1-50 microg ml(-1), respectively. The relative standard deviations (n=5) were 1.7-3.0%. The present method was successfully applied to the determination of glyphosate in urine and serum.

Simultaneous separation of inorganic anions and cations by using anion-exchange and cation-exchange columns connected in tandem in ion chromatography

Inorganic anions and cations in environmental waters were determined by ion chromatography. Stationary and mobile phases were examined for the simultaneous separation of both anions and cations. Cations detection by UV detection requires a mobile phase with a UV absorbing additive, which indirectly visualizes cations as negative peaks. Simultaneous separation of anions and cations were achieved when using an eluent that consists of inorganic acid with weak basic amino acid as additives. It was convenient to separate both anions and cations by coupling anion-exchange and cation-exchange columns in tandem. The order of the separation columns connected affected the elution profiles. When the eluent comprises of multiple anions and a single cation, the anion-exchange column should be connected in the upper stream, whereas when the eluent comprises multiple cations and a single anion, the cation-exchange column should be connected in the upper stream. Use of switching valves also allowed simultaneous separation of anions and cations in a single chromatographic run. In the present work, operating conditions were optimized for the simultaneous separation of anions and cations.

Separation of aliphatic carboxylic acids and benzenecarboxylic acids by ion-exclusion chromatography with various cation-exchange resin columns and sulfuric acid as eluent.

The application of various hydrophilic cation-exchange resins for high-performance liquid chromatography (sulfonated silica gel: TSKgel SP-2SW, carboxylated silica gel: TSKgel CM-2SW, sulfonated polymethacrylate resin: TSKgel SP-5PW, carboxylated polymethacrylate resins: TSKgel CM-5PW and TSKgel OA-Pak A) as stationary phases in ion-exclusion chromatography for C1-C7 aliphatic carboxylic acids (formic, acetic, propionic, butyric, isovaleric, valeric, isocaproic, caproic, 2-methylhexanoic and heptanoic acids) and benzenecarboxylic acids (pyromellitic, trimellitic, hemimellitic, o-phthalic, m-phthalic, p-phthalic, benzoic, salicylic acids and phenol) was carried out using diluted sulfuric acid as the eluent. Silica-based cation-exchange resins (TSKgel SP-2SW and TSKgel CM-2SW) were very suitable for the ion-exclusion chromatographic separation of these benzenecarboxylic acids. Excellent simultaneous separation of these benzenecarboxylic acids was achieved on a TSKgel SP-2SW column (150 x 6 mm I.D.) in 17 min using a 2.5 mM sulfuric acid at pH 2.4 as the eluent. Polymethacrylate-based cation-exchange resins (TSKgel SP-5PW, TSKgel CM-5PW and TSKgel OA-Pak A) acted as advanced stationary phases for the ion-exclusion chromatographic separation of these C1-C7 aliphatic carboxylic acids. Excellent simultaneous separation of these C1-C7 acids was achieved on a TSKgel CM-5PW column (150 x 6 mm I.D.) in 32 min using a 0.05 mM sulfuric acid at pH 4.0 as the eluent.

Nickel–titanium alloy electrodes for stable amperometric detection of underivatized amino acids in anion-exchange chromatography

Nickel-titanium (Ni-Ti) alloy electrode was used as an electrochemical detector for the analysis of underivatized amino acids in flow systems. In strong alkaline solution, an oxide film on the Ni-Ti alloy electrode surface exhibited a high catalytic activity toward the oxidation of amino acids. Cyclic voltammetry experiments confirmed that electrogenerated Ni(III)O(OH) functioned as the key redox mediator associated with the oxidation of the amine group in amino acids. The electrochemical behavior of the Ni-Ti electrode in alkaline medium was very similar to the Ni electrode. However, the oxide film was found to be much stable on Ni-Ti than on Ni. Consequently, the Ni-Ti alloy electrode exhibited an excellent stability for constant-potential amperometric detection of amino acids in flow systems. For example, the relative standard deviation (R.S.D.) for the repetitive 100 injections of 50 muM (1.2 nmol) glycine over 10 h was less than 1%. It was postulated that the presence of Ti in the alloy stabilizes the microstructure of oxide layer on the electrode surface. The sensitivities of amino acids at the electrode were different, depending on their chemical structures. The detection limits obtained in a range from 0.9 pmol for arginine to 90.2 pmol for leucine and isoleucine. The Ni-Ti alloy electrodes have been demonstrated to be very suitable for the amperometric detection of underivatized amino acids in anion-exchange chromatography.

Measurement of nitric oxide released in the rat heart with an amperometric microsensor

Nitric oxide (NO) plays an important role in various physiological processes, acting either as an intra- and intercellular messenger or as a toxic agent. The detection and quantification of NO have been accomplished by a variety of methodologies. In the present study, real-time production of NO in the rat heart was continuously measured by using a novel copper-platinum microparticle-modified NO electrochemical microsensor. The linearity range of the microsensor is between 8.0 x 10(-8) and 4.8 x 10(-6) mol L-1 and the detection limit is 3.0 x 10(-8) mol L-1. NO release from the rat heart stimulated by the agonists L-arginine and acetylcholine was observed, and the responses were decreased by the NO synthase inhibitor L-N omega-nitroarginine. In addition, the effect of sodium nitroprusside (SNP), a NO donor, was also studied. SNP increases the concentration of NO in the rat heart. The experiments showed that electrochemical detection is suitable for detecting and quantifying NO in biological systems.

Simultaneous determination of inorganic nitrogen species by microcolumn ion chromatography.

Inorganic nitrogen species (nitrate, nitrite and ammonium ions) were simultaneously determined by microcolumn ion chromatography. Nitrate and nitrite were determined by UV detection at 206 nm, whereas ammonium ion was determined by fluorescence detection at excitation 410 nm and emission 470 nm. The latter fluorescence detection is based on the postcolumn reaction of ammonium ion with o-phthalaldehyde in the presence of 2-mercaptoethanol. Effects of the reagent concentration, pH, and other reaction conditions on the signal intensity were examined, and the optimum condition was explored. The present method allowed simultaneous determination of nitrate, nitrite and ammonium ions in river water.

Determination of inorganic anions via postcolumn reaction with iodide in ion chromatography

Inorganic anions were determined as triiodide by postcolumn reaction with iodide under an acidic condition with help of alpha-cyclodextrin in ion chromatography. Analytes reacting with iodide to produce iodine could be determined by the present method. The analytes were indirectly detected at 287 or 355 nm. The presence of alpha-cyclodextrin caused an increase in the concentration of triiodide, leading to improvement of the sensitivity. The present system achieved good selectivity to iodate, bromate and nitrite as well as good repeatability under the optimum conditions. The determination of nitrite in river water was possible.

Separation of enantiomers by microcolumn liquid chromatography with methylated β-cyclodextrin as mobile phase additive

Enantiomers can be separated by microcolumn liquid chromatography with methylated β-cyclodextrin (β-CD) as a mobile phase additive. Effects of the mobile phase composition on the retention behaviour of the analytes were examined. The separation factor achieved with heptakis(2,3,6-tri-O-methyl)-β-CD as the chiral selector for 1,1′-binaphthyl-2,2′-diyl hydrogenphosphate enantiomers was up to 3. Heptakis(2,6-di-O-methyl)-β-CD achieved poor enantioselectives for the enantiomers examined.