Electrochemical Oxidation of l-selenomethionine and Se-methylseleno-l-cysteine at a Thiol-Compound-Modified Gold Electrode: Its Application in a Flow-Through Voltammetric Sensor.

A flow-electrolytic cell that consists of a bare gold wire or of different thiol-compound-modified gold electrodes (such as 2,4-thiazolidinedione, 2-mercapto-5-thiazoline, 2-mercaptothiazoline, l-cysteine, thioglycolic acid) was designed to be used in a voltammetric detector to identify l-selenomethionine and Se-methylseleno-l-cysteine using high-performance liquid chromatography. Both l-selenomethionine and Se-methylseleno-l-cysteine are more efficiently electrochemically oxidized on a thiol/gold than on a bare gold electrode. For the DC mode, and for measurements with suitable experimental parameters, a linear concentration from 10 to 1600 ng·mL-1 was found. The limits of quantification for l-selenomethionine and Se-methylseleno-l-cysteine were below 10 ng·mL-1. The method can be applied to the quantitative determination of l-selenomethionine and Se-methylseleno-l-cysteine in commercial selenium-containing supplement products. Findings using high-performance liquid chromatography with a flow-through voltammetric detector and ultraviolet detector are comparable.

Evaluating a Cobalt-Tetraphenylporphyrin Complex, Functionalized with a Reduced Graphene Oxide Nanocomposite, for Improved Tooth Whitening.

OBJECTIVES: To study using cobalt-tetraphenylporphyrin/reduced graphene oxide (CoTPP/RGO), a nanocomposite highly catalytic both for oxidizing and for reducing hydrogen peroxide (H2 O2 ), to whiten teeth. METHODS: Dyes (D&C Red 34, Orange No. 4), tea, and betel nuts (Areca catechu) were used to stain the tooth specimens for three days and subsequently bleached using H2 O2 alone, H2 O2 plus CoTPP, or H2 O2 plus CoTPP/RGO for 0.5-70 hours. The process was photographed using an electronic chromometer and a camera. Color change was assessed after each session. The results of bleaching teeth with and without photoirradiation were compared. RESULTS: CoTPP/RGO increased the tooth-whitening efficacy of H2 O2 for specimens stained with dyes, tea, and betel nuts. Using lamps (photoactivation) (wavelengths: 254 nm and 310 nm) to catalyze the H2 O2 bleaching agent reduced the bleaching treatment time. CLINICAL SIGNIFICANCE: First, the Co/TPP/RGO complex allows improved tooth bleaching and shorter treatment times. Second, because the Co/TPP/RGO complex bleached D&C Red 34 at a similar rate and to a similar degree as tea and other natural agents stain teeth, it is a convenient staining agent for studying many vital aspects of tooth bleaching. (J Esthet Restor Dent 28:321-329, 2016).

Electrochemical oxidation of cysteine at a film gold modified carbon fiber microelectrode its application in a flow-through voltammetric sensor.

A flow-electrolytical cell containing a strand of micro Au modified carbon fiber electrodes (CFE) has been designedand characterized for use in a voltammatric detector for detecting cysteine using high-performance liquid chromatography. Cysteine is more efficiently electrochemical oxidized on a Au /CFE than a bare gold and carbon fiber electrode. The possible reaction mechanism of the oxidation process is described from the relations to scan rate, peak potentials and currents. For the pulse mode, and measurements with suitable experimental parameters, a linear concentration from 0.5 to 5.0 mg·L(-1) was found. The limit of quantification for cysteine was below 60 ng·mL(-1).

Studies on the electrochemical behavior of thiazolidine and its applications using a flow-through chronoamperometric sensor based on a gold electrode.

The electrochemical behaviors of thiazolidine (tetrahydrothiazole) on gold and platinum electrodes were investigated in a Britton-Robinson buffer (pH 2.77-11.61), acetate buffer (pH 4.31), phosphate buffer solutions (pH 2.11 and 6.38) and methanol or acetonitrile containing various supporting electrolytes. Detection was based on a gold wire electrochemical signal obtained with a supporting electrolyte containing 20% methanol-1.0 mM of phosphate buffer (pH 6.87, potassium dihydrogen phosphate and dipotassium hydrogen phosphate) as the mobile phase. Comparison with results obtained with a commercial amperometric detector shows good agreement. Using the chronoamperometric sensor with the current at a constant potential, and measurements with suitable experimental parameters, a linear concentration from 0.05 to 16 mg L-1 was found. The limit of quantification (LOQ) of the method for thiazolidine was found to be 1 ng.

Study of the aerosol fragrances of eugenol derivatives in Cananga odorata using diffuse reflectance infrared Fourier transform spectroscopy and gas chromatography.

The purpose of this study was to develop and test a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) method, a fast and non-destructive method without extraction, and compare it with the standard gas chromatography (GC) method currently used. A micro-orifice uniform deposit impactor (MOUDI) was used to sample all the size distributions of the aerosol particles of essential oils to investigate the relation between size distributions and the indoor concentration distributions of ylang essential oils. Correlation coefficients for DRIFTS and GC were 0.9904, 0.9910, 0.9913, and 0.9983 for eugenol, isoeugenol, methyl ether, and eugenyl acetate, respectively. The results showed that the concentrations of the four eugenol derivatives of smoke were approximately three times higher than those of mist. Additionally, the major size distributions of aerosol were 0.19 microm and 1.8 microm for the smoke and mist methods, respectively. Because these two methods produce similar results, DRIFTS is a practical method for assessing these fragrances in aerosols.

Electrochemical reduction of coumarins at a film-modified electrode and determination of their levels in essential oils and traditional Chinese herbal medicines.

The electrochemical reduction of coumarins on glassy carbon and electrodeposited metal electrodes was investigated in a Britton-Robinson buffer (pH 1.87-11.98). The effects of various factors, such as the deposition material, time, and concentration of mercury, on the precision of the analysis were explored. The possible reaction mechanism of the reduction process with regards to scan rates, peak potentials, and currents is discussed. Electroreduction was used to quantitatively determine the levels of coumarins in some essential oils and traditional Chinese herbal medicines. A comparison with high performance liquid chromatography analysis results shows good agreement.

Determining urinary trace elements (Cu, Zn, Pb, As, and Se) in patients with bladder cancer.

OBJECTIVES: Trace elements are essential components of biological structures, but they can be toxic at concentrations beyond those necessary for their biological functions. METHODS: A study group of 30 patients with bladder cancer and a control group of 30 healthy volunteers were measured for trace elements using a graphite furnace atomic absorption spectrophotometer. RESULTS: Urinary zinc and selenium levels in patients were significantly (P < 0.05) higher than those in controls, but urinary copper, arsenic, and lead were not significantly different. CONCLUSION: This case-control study suggests that zinc and selenium concentrations are associated with the proliferation of bladder cancer cells because zinc and selenium are excreted in the urine of bladder cancer patients.

Vehicle and enhancer effects on human skin penetration of aminophylline from cream formulations: evaluation in vivo.

The effects of four essential oils (rosemary, ylang, lilacin, and peppermint oils), and three plant oils (jojoba oil, corn germ oil, and olive oil) on the permeation of aminophylline were studied using human skin. The permeation effects of these oils were compared with those of three chemical penetration enhancers. Although all oils enhanced the permeation of aminophylline, their effects were less than that of ethanol. Jojoba oil was found to be the most active, causing about a 32% peak height decrease of N-H bending absorbances in comparison with the control, while peppermint, lilacin, rosemary, and ylang oils caused 28%, 24%, 18%, and 12% peak height decreases, respectively. Microemulsions containing 10% jojoba oil and 30% corn germ oil were found to be superior vehicles for the percutaneous absorption of aminophylline. Comparision with results obtained from high-performance liquid chromatography shows good agreement.

Simultaneous determination of p-aminobenzoic acid and its metabolites in the urine of volunteers, treated with p-aminobenzoic acid sunscreen formulation.

p-Aminobenzoic acid (PABA) and its metabolites (p-aminohippuric acid, p-acetamidobenzoic acid, and p-acetamidohippuric acid) were detected using high-performance liquid chromatography with an electrochemical (carbon paste) detector (HPLC-ECD). For direct current (dc) mode, with the current at a constant potential, and measurements with suitable experimental parameters, a linear concentration from 0.125 to 1.80 microg/ml was found. The detection limit was approximately 2.0 ng/ml. A carbon paste coulometric detector was used to demonstrate that PABA and its metabolites are electrochemically oxidized in acidic media, and to determine, by analyzing human urine, the percutaneous absorption of PABA and its metabolites. Findings using HPLC-ECD and HPLC with an ultraviolet detector (HPLC-UV) were comparable.

Simultaneous determination of urinary metabolites of methoxypsoralens in human and Umbelliferae medicines by high-performance liquid chromatography.

A high-performance liquid chromatography method has been developed for the determination of coumarins and furocoumarins (psoralens). Nine coumarins and furocoumarins are separated simultaneously on a Hypersil C(8) (25 cm x 4.6-mm i.d.) column with a gradient of methanol and acetonitrile aqueous solution as mobile phase at 1.0 mL/min with two-channel UV-vis absorbance detection. The limits of detection are 0.366, 0.219, 0.317, 0.440, 0.536, 0.300, 0.531, 0.531, 0.237, and 0.280 ng/mL for coumarin, 7-hydroxycoumarin, 7-methoxycoumarin, citropten (5,7-dimethoxycoumarin), 7-ethoxy-4-methylcoumarin, psoralen, xanthotoxin (8-methoxypsoralen), bergapten (5-methoxypsoralen), isopimpinellin (5,8-dimethoxypsoralen), and imperatorin (9-isopenteneoxypsoralen), respectively. Human urine is analyzed 1-6 days after ingestion of the oral Chinese medicines. This lead to the conclusion that the concentration of coumarins and furocoumarins is higher than that of the control urine. The coumarins and furocoumarins are detected at 312 and 249 nm, respectively.

Simultaneous determination of chlorinated bacteriostats in cosmetic and pharmaceutical products.

A high-performance liquid chromatography method has been developed for simultaneous determination of triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) and triclocarban (3,4,4'-trichlorocarbanilide) in cosmetic and pharmaceutical products. The two compounds could be separated on a Nucleosil C(18) column and eluted with acetonitrile and water (70:30, v/v) as the mobile phase and detected with a differential refractive index detector. The retention times of triclosan and triclocarban were 5.81 and 2.99 min, respectively. The results obtained were in good agreement with those obtained by a differential pulse voltammetric method.

Simultaneous determination of oxidative hair dye p-phenylenediamine and its metabolites in human and rabbit biological fluids.

A liquid chromatography with an electrochemical detector method has been developed for the quantitative measurement for three diamine derivatives (p-phenylenediamine, N,N(')-p-phenylenebisacetamide, and 4-aminoacetanilide) in human urine and rabbit blood, urine, and feces. The detection cell consisted of a glassy carbon electrochemical signal obtained with a supporting electrolyte containing 20% methanol-5mM octylammonium orthophosphate (pH 6.30) as the mobile phase. A comparison of the results obtained from HPLC-UV shows agreement.

Determination of 5-methoxypsoralen in human serum.

A high performance liquid chromatography with fluorometric and ultraviolet detection described to quantify 5-methoxypsoralen (5-MOP) percutaneous absorption in humans after the application of an essential oil, as well as 5-MOP in bergamot oil and cosmetics by fluorometric and voltammetric measurement, respectively. A muBondapack C(18) analytical column (particle size 5 microm, 3.9 x 300 mm) eluted with acetonitrile-tetrahydrofuran-water (70:15:15, v/v/v) containing 0.07% trifluoroacetic acid. The quantification limits are 0.05 and 0.26 ng for 5-MOP and 5-geranoxypsoralen, respectively. For fluorometric measurement was found linear over the range 0.05-3.00 microg/ml for psoralens. Five volunteers blood samples were collected over a 2-day period were investigated before and after treatment with bergamot oil. Serum levels of 5-MOP were significantly increased from the 4 h after the application of bergamot essential oil. The hourly mean levels were significantly higher after the application of bergamot essential oil compared to baseline values.

Ion chromatography studies of quaternary ammonium halide solutions and the determination of pharmaceuticals.

The feasibility of using ion chromatography (IC) in solutions containing quaternary ammoniums is studied. The results establish the applicability of IC for the determination of halide ions in a pharmaceutical sample without interferences by various excipient ions. For IC measurements with suitable methodical parameters, linearity is maintained over the range of 20 to 200 mg/L and 10.0 to 250 mg/L for the chloride and bromide of quaternary ammoniums, respectively. A comparison of the anion results obtained from differential pulse voltammetry shows good agreement.