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We describe a method for the determination of the two major urinary metabolites of vitamin K as the methyl esters of their aglycone structures, 2-methyl-3-(3′-3′-carboxymethylpropyl)-1,4-naphthoquinone (5C-aglycone) and 2-methyl-3-(5′-carboxy-3′-methyl-2′-pentenyl)-1,4-naphthoquinone (7C-aglycone), by HPLC with electrochemical detection (ECD) in the redox mode. Urinary salts were removed by reversed-phase (C18) solid-phase extraction (SPE), and the predominantly conjugated vitamin K metabolites were hydrolyzed with methanolic HCl. The resulting carboxylic acid aglycones were quantitatively methylated with diazomethane and fractionated by normal-phase (silica) SPE. Final analysis was by reversed-phase (C18) HPLC with a methanol-aqueous mobile phase. Metabolites were detected by amperometric, oxidative ECD of their quinol forms, which were generated by postcolumn coulometric reduction at an upstream electrode. The assay gave excellent linearity (typically, r2 ⩾ 0.999) and high sensitivity with an on-column detection limit of

A high-performance liquid chromatographic method with electrochemical detection (HPLC-ED) at a boron-doped diamond film electrode with preliminary separation and preconcentration by solid-phase extraction (SPE) has been developed for the determination of 1-hydroxypyrene (1-HP) in human urine. 1-HP is among the most widely used biomarkers of exposure to polycyclic aromatic hydrocarbons. Optimal HPLC-ED conditions have been found: mobile phase methanol-0.05 mol L phosphate buffer pH 5.0 (80:20, v/v), detection potential +1,000 mV versus Ag/AgCl (3 mol L KCl), and flow rate 0.8 mL min. For SPE, LiChrolut RP-18 E cartridges were used. The extraction yield was (87.0 ± 5.8) % ( n = 5). The concentration dependence of 1-HP was measured in the concentration range from 0.01 to 10 μmol L (2.18-2,180 μg L) using methanolic solutions resulting from the SPE pretreatment of spiked human urine samples. The limit of detection (signal-to-noise ratio 3) and the limit of quantification (signal-to-noise ratio 10) of the biomarker were 0.013 μmol L (2.84 μg L) and 0.043 μmol L (9.39 μg L), respectively, which is sufficient for its determination in the urine of persons exposed to polycyclic aromatic hydrocarbons. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Methylparaben (MePa), ethylparaben (EtPa) and propylparaben (PrPa) have been widely used, among others, as chemical preservatives in cosmetics, drugs and foods. As these compounds are linked with allergies, dermatitis and estrogenic properties, it is necessary to control the concentration of these substances in different matrices. The aim of this paper are: to evaluate the electrochemical behavior of parabens on the boron-doped diamond (BDD) electrode and the development of a chromatographic method, with electrochemical detection (HPLC-ED), for determination of parabens in shampoo. A BDD (8000ppm) electrode was adapted in a thin layer mode analytical cell consisting of a stainless steel and a platinum wire as reference and auxiliary electrodes, respectively. Chromatographic separations were obtained with a reversed phase C8 analytical column and a mobile phase of 0.025molL−1 disodium phosphate, pH 7.0, and acetonitrile (40:60, v/v), delivered at a flow rate of 1.0mL min−1. Sample preparation was performed by solid phase extraction using C18 cartridges and acetonitrile for elution. Benzylparaben was employed as internal standard. The HPLC-ED method developed, using the BDD electrode, was validated for the determination of parabens in shampoos and presented adequate linearity (>0.999), in the range of 0.0125–0.500% (w/w), detectability 0.01% (w/w), precision (RSD of 2.3–9.8%) and accuracy (93.1–104.4%) and could be applied for routine quality control of shampoos containing MePa, EtPa and PrPa. [Copyright &y& Elsevier]

The oxidative behaviour of pimozide was studied in hydroalcoholic media (10+90 methanol–H2O, pH range 2–7.5) at carbon based electrodes. Pimozide was irreversibly oxidized at high positive potentials, resulting in the formation of a couple with a reduction and re-oxidation peak at much lower potentials. The response was evaluated with respect to pH, scan rate, addition of surfactant and other variables. Using differential pulse voltammetry (DPV), the drug yielded a well-defined voltammetric response in Britton–Robinson buffer, pH 2.1 at +1.1 V (versus Ag/AgCl) on glassy carbon electrode. The process could be used to determine pimozide concentrations in the range 8×10−7–1×10−4 M. Applicability to tablets and human serum analysis was illustrated. Furthermore, a high-performance liquid chromatographic method with electrochemical detection (HPLC–EC) was developed, which allowed pimozide to be detected down to a level of 2.7×10−10 M (0.25 ppb). [Copyright &y& Elsevier]

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent pulmonary carcinogen found in unburned tobacco and tobacco smoke, and is believed to play an important role in human tobacco-induced cancers. In previous studies, NNK has been reported to induce oxidative DNA damage, and to alter DNA repair processes, effects that could contribute to pulmonary tumorigenesis in rodent models. The goal of this study was to determine the effects of NNK on levels of 8-hydroxydeoxyguanosine (8-OHdG), a biomarker of DNA oxidation, and activity of base excision repair (BER), which repairs oxidative DNA damage. Female A/J mice were treated with a tumorigenic dose of NNK (10μmol) i.p. At 1, 2 and 24h post treatment, there were no statistically significant differences in lung or liver 8-OHdG levels between control and NNK-treated mice (P>0.05). Furthermore, NNK did not alter lung or liver BER activity compared to control at any time point (P>0.05). In summary, acute treatment with a tumorigenic dose of NNK did not stimulate oxidative DNA damage or significantly alter BER activity, and these effects may not be major mechanisms of action of NNK in mouse models., (Copyright © 2013 Elsevier B.V. All rights reserved.)