Application of l-cysteine-capped nano-ZnS as a fluorescence probe for the determination of proteins

Nanometer-sized l-cysteine-capped ZnS particles have been synthesized and used as a fluorescence probe to investigate the effect of proteins on fluorescent intensity. With =190 nm, maximum and constant synchronous fluorescence enhancement was produced at 267 nm and pH 5.12 in the presence of proteins. A highly sensitive synchronous fluorescence method for the rapid determination of proteins has been developed. Under optimum conditions, calibration graphs are linear over the range 0.03–8.0 g mL^–1 for bovine serum albumin (BSA), 0.01–6.0 g mL^–1 for human serum albumin (HSA), 0.05–8.0 g mL^–1 for -globulin (-G), and 0.04–4.0 g mL^–1 for ovalbumin, respectively. The relative standard deviations of seven replicate measurements were 1.75% for 1.0 g mL^–1 BSA, 1.90% for 1.0 g mL^–1 HSA, 1.65% for 1.0 g mL^–1 -G, and 2.32% for 1.0 g mL^–1 ovalbumin.     

Determination of Dextromethorphan and Dextrorphan in Human Urine by High Performance Liquid Chromatography for Pharmacogenetic Investigations

The aim of the present study was to develop a sensitive method to measure dextromethorphan and dextrorphan in urine by HPLC to support pharmacogenetic studies in ethnic groups. Linearity was assessed in the range: 0.015–10 g mL^–1 for dextromethorphan and 1-10 g mL^–1 for dextrorphan. Inter and intra-day coefficients of variation were < 10%. Limits of detection and quantitation were 0.003 g mL^–1 and 0.015 g mL^–1 for dextromethorphan and 0.24 g mL^–1 and 1.0 g mL^–1 for dextrorphan, respectively. The method is reliable in helping determine the phenotype of Mexican ethnic groups using model drugs such as dextromethorphan.     

Simultaneous Determination of Four Active Components in a Compound Formulation by Liquid Chromatography

Summary A rapid and accurate LC method is described for simultaneous determination of pseudoephedrine hydrochloride (PSE), acetaminophen (AMP), dextromethorphen hydrobromide (DEX), and diphenhydramine hydrochloride (DPH) in a compound formulation. Chromatographic separation of the four drugs was achieved on a Hypersil CN column (150 mm × 4.6 mm, 5 m particle) by use of a mobile phase comprising a mixture of 3 mM ion-pairing solution, 2% aqueous triethylamine solution, and 2 M phosphoric acid, 68:48:88 (v/v), pH 3.0, delivered at 1.0 mL min^–1. Compounds were detected at 215 nm and the run time was less than 10 min. The linearity, accuracy, and precision of the method were found to be acceptable over the concentration ranges 6.1–36.4 g mL^–1 for PSE, 65.0–390.0 g mL^–1 for AMP, 3.1–18.6 g mL^–1 for DEX, and 5.0–30.0 g mL^–1 for DPH.     

Separation of linear gramicidins using carbon dioxide-containing mobile phases

Packed-column supercritical-fluid chromatography (pSFC) is presented as a novel method for separating and analyzing gramicidin samples. By use of methanol-modified carbon dioxide as a mobile phase the pentadecapeptides gramicidin A (gA), gramicidin B (gB), and gramicidin C (gC) are readily separated and eluted from a PRP-1 poly(styrene–divinylbenzene) column. Although optimum separation conditions are typically achieved near a column temperature of 40°C, a column pressure of 11 MPa, and 30% methanol modifier, pressure and modifier gradients around these values are also found to improve the overall separation time. Measurements indicate that the mobile phase solubility of gramicidin under these conditions is 5.0±0.4 g mL^–1. Collection of individual peaks during chromatography achieved analytical-scale isolation of 2 g refined gC from 20 g injected gramicidin D. Further, supercritical-fluid extraction of 200 g gramicidin D from a Chromosorb 102 support packed into the vessel produced 57 g gA in 90% purity. The results establish that carbon dioxide-based mobile phases can be successfully used for the separation of individual gramicidin species.     

Determination of 6-amino-2,2-dimethyl-1,3-dioxepan-5-ol by postcolumn derivatization witho-phthalaldehyde/2-mercapto-ethanol after ion-pair chromatography

Summary A high-performance liquid chromatographic method is discribed for the determination of 6-amino-2,2-dimethyl-1,3-dioxepan-5-ol using Spherisorb ODS II stationary phase and mobile phase 30:70 (v/v) methanol: aqueous 1-octane sulfonic acid. Detection was fluorimetric following postcolumn derivatization with o-phthaladehyde/2-mercaptoethanol. The procedure was applied to the analysis of aqueous solutions and microcrystalline suspensions in liquid paraffin, prepared for investigation of the toxicological profile. The method was validated for selectivity, linearity of detector response, repeatability, limit of detection and quantitation. The HPLC method was selective. The instrumental limit of detection was 0.5 ng per injection (0.05 g mL^–1). The method detection limits were 0.5 g mL^–1 aqueous solution and 5 g mL^–1 liquid paraffin suspension, the quantitation limit 0.05 mg mL^–1 aqueous solution and 1.0 mg mL^–1 liquid paraffin. Linearity was within 0.94–47.1 g mL^–1. Intra-assay accuracy accounted for 99–100% in the range 0.05–226 mg mL^–1 aqueous solution, intra-assay precision for 2% (C.V.). For microcrystalline liquid paraffin suspensions with 1 and 250 mg mL^–1 99 and 109% was found for intra-assay accuracy. Intra-assay precision was 5% (C.V.). Reliable results over a wide concentration range can be obtained. The procedure is considered valid for determination of the analyte in aqueous solution or microcrystalline paraffin oil suspensions.     

Extractive spectrophotometric determination of dioxouranium(VI) with the sodium salt of hexamethyleneiminecarbodithioate

The optimum conditions for the extractive spectrophotometric determination of dioxouranium(VI) with hexamethyleneiminecarbodithioate(HMICdt) have been established. Dioxouranium(VI) reacts with this ligand at pH 4.5 to form a yellowish-orange uncharged 12 metal-ligand complex which can be extracted by chloroform. The calibration graph was linear in the range of 1–20 g ml^–1 of dioxouranium(VI) at 335 nm. The molar absorptivity of the extracted species is 5.952×10³ l mol^–1 cm^–1 with Sandell's sensitivity of 0.04 g cm^–2. The average of 10 determinations of dioxouranium was 49.75 g for the samples containing 50 g of U(VI) and the variation from the mean at 95% confidence limit was 49.75±0.5955.     

Determination of ochratoxin A in Portuguese rice samples by high performance liquid chromatography with fluorescence detection

A sensitive and accurate analytical method for the determination of ochratoxin A (OTA) in rice, based on extraction with phosphate-buffered saline/methanol, an immunoaffinity column (IAC) for clean-up, and high performance liquid chromatography with fluorescence detection (HPLC-FD), is described. The limit of quantification of the proposed method was 0.05 g kg^–1. Recovery of OTA from rice samples spiked at 0.05 g kg^–1 was 92%, with a within-day RSD of 5.4%. The proposed method was applied to 42 rice samples from Portugal and the presence of OTA was found in six samples at concentrations ranging from 0.09 to 3.52 g kg^–1. The identification of OTA was confirmed by methyl ester derivatization and then HPLC analysis. The daily intake of OTA by the Portuguese population was also estimated.     

Determination of pentachlorophenol residues in wine and corks by solvent extraction methodology and specific gas chromatography detection

Summary A gas chromatographic methodology with selective detection is presented for the analysis in wines and corks of pentachlorophenol residues, which are suspected to be the most likely precursors of some off-flavours described in several wine samples. After derivatisation, pentachlorophenol acetate residues were monitored by electrolytic conductivity detection and/or mass spectrometric detection in the selective ion mode at m/z 264 and 266. Recoveries varied from 80 to 96% for wine samples fortified with 5 to 100 g l^–1 and from 83 to 91% for corks (fortified at 25 to 100 g kg^–1). The proposed methodology allowed for a determination limit of g l^–1 for wine and 10 g kg^–1 for corks.     

Simultaneous determination of neodymium and erbium in rare earth mixture with 5,7-dibromo-8-hydroxyquinoline and TX-100 by third-derivative spectrophotometry

The absorption spectra of 4f electron transitions of the complexes of neodymium and erbium with 5,7-dibromo-8-hydroxyquinoline in the presence of octylphenol poly(ethyleneglycol)ether have been studied by normal and third-derivative spectrophotometry. The proposed method is free of interference of other rare earths. The calibration graphs were linear up to 18 g/ml of neodymium and 21 g/ml of erbium (in the final solution). The derivative molar absorptivities are 395 l.mol^–1.cm^–1 for neodymium and 3421.mol^–1.cm^–1 for erbium. The corresponding values of Sandell's sensitivity were 0.36 and 0.49 g.cm^–1, respectively. The relative standard deviations evaluated from ten independent determinations of 2.5 g/ml of neodymium and erbium are 1.5 and 3.8% for neodymium and 1.8 and 4.1% for erbium in absence and presence of 70 g of lanthanum, respectively. The detection limits (signal to noise ratio=2) are 0.23 g/ml for neodymium and 0.30 g/ml for erbium. The method has been used for the determination of neodymium and erbium in mixed rare earths with satisfactory results.     

Development and validation of a novel HPLC/ELSD method for the direct determination of tobramycin in pharmaceuticals,plasma, and urine

A novel method for the direct determination of the aminoglycoside tobramycin was developed and validated based on reversed-phase high-performance liquid chromatography (RP-HPLC) with evaporative light scattering detector (ELSD). Using a Waters ODS-2 C18 Spherisorb column with an evaporation temperature of 45°C and nitrogen pressure of 3.5 bar, the selected mobile phase consisted of water/acetonitrile 55:45 containing 1.5 mL L^–1 HFBA (11.6 mM) in an isocratic mode at a rate of 1.0 mL min^–1. Tobramycins retention time was 4.3 min with an asymmetry factor of 1.7. A logarithmic calibration curve was obtained from 1 to 38 g mL^–1 (r > 0.9998). LOD was 0.3 g mL^–1; within-day %RSD was 1.0 (n = 3, 4.7 g mL^–1) and between-day %RSD was 1.1 (3 days within a week). The developed method was applied to the determination of tobramycin in a pharmaceutical crude substance and formulations (eye drops and ointments). Dilution experiments revealed the absence of interference from excipients (no constant and proportional errors); recovery from spiked samples was 99–103% with %RSD < 2.2 (n = 3×3). The developed HPLC/ELSD method was also found to be applicable in the determination of tobramycin in human plasma (0.6–12.5 g mL^–1) and urine (1.5–12.5 g mL^–1) after solid-phase extraction using carboxylate cartridges followed by solvent evaporation (×2 preconcentration). A mean recovery of 86% for plasma and 91% for urine was obtained.     

Capacitive chemical sensor for fenvalerate assay based on electropolymerized molecularly imprinted polymer as the sensitive layer

A capacitive chemical sensor for fenvalerate is reported. By using ac impedance measurements the sensor has been based on the decrease in capacitance caused by the analyte used as the template in the formulation of an electropolymerized molecularly imprinted polymer as receptor layer. Improvement of the insulating properties of the sensor was investigated in detail. The capacitive sensor was prepared by a deposition of a self-assembled monolayer of 2-mercaptobenzimidazole (2-MBI) before electropolymerization of 2-MBI and subsequent treatment with n-dodecanethiol to eliminate pinholes and defects in the polymerized 2-MBI film. From the calibration curve concentrations of fenvalerate up to 9 g mL^–1 could be detected with a linear determination range up to 5 g mL^–1 and a detection limit of 0.36 g mL^–1. No significant interference was observed from common pyrethroid insecticides.     

LC Method for the Determination of Multiple Components in a Compound Cold Formulation

An isocratic liquid chromatographic method for determination of acetaminophen (AMP), caffeine (CAF), chlorphenamine maleate (CPM) and guaiacol glyceryl ether (GGE) in a compound cold formulation is described. Separation and quantitation were achieved on a Diamonsil C18 column using a binary mixture of methanol and 1.5% aqueous acetic acid (55: 45, v/v, pH 3.6) as mobile phase delivered at 0.4 mL min^–1. Single wavelength detection was at 220 nm for all four drugs and the run time was < 10 min. The linearity, accuracy and precision of the method were found to be acceptable over the concentration ranges: 16.0–127.8 g mL^–1 for AMP, 6.0–48.2 g mL^–1 for CAF, 5.0–40.0 g mL^–1 for CPM and 10.1–80.6 g mL^–1 for GGE.     

Simultaneous determination of lomefloxacin,fenbufen and felbinac in human plasma using high performance liquid chromatography

Summary A simple, specific, and sensitive high-performance liquid chromatography method has been developed for simultaneous determination of the lomefloxacin, febufen, and felbinac in human plasma. Plasma-spiked with internal standard, was vortex-mixed for 1 min with a mixture of dichloromethane-diethylether (80:20, v/v). The evaporated extract was dissolved in 0.02 M NaOH. The extracts were chromatographed on an Supelcosil LCSAX column (5 m 250×4.6 mm I.D.) equipped with a guard column with a mibile phase composed of acetonitrile and phosphate buffer, with ultraviolet detection. Drugs were resolved at ambient temperature on a flow rate was 1.2 mL min^–1, and monitoring was performed at 280 nm. The detection limits for lomefloxacin was 0.05 g mL^–1, 0.02 g mL^–1 for fenbufen and 0.03 g mL^–1 for felbinac. No interference from other commonly administered drugs or endogenous substances was observed. The method is fast since it involves two extraction steps followed by evaporation of organic solvent and chromatography of the residue. This method was found to be applicable to pharmacokinetic and pharmacodynamic studies of each drug after the concomitant administration of lomefloxacin and febufen.     

Determination of Methacycline and Glucose in Biological Fluids by Europium(III)-Sensitized Luminescence

Complexation in the Eu(III)–methacycline and Eu(III)–methacycline–hydrogen peroxide systems was studied by luminescence. It was proposed to use the studied complexes as analytical forms for the luminescence determination of methacycline in blood plasma (lower determination limit 2.5 g/mL) and urine (25 g/mL) and for the indirect determination of 0.025–0.7 mM glucose in blood plasma.     

Di-μ-hydroxo bridge-cleavage reactions between [Co(nta)(μ-OH)]2 2− and different monodentate ligands

The cleavage of the di--hydroxo bridges of [Co(nta)(-OH)]₂ ^2– by dimethylaminopyridine (dmap) and pyridine (py) has been investigated. [Co(nta)(-OH)]₂ ^2– equilibrates rapidly in aqueous basic solutions with a mono--hydroxo bridged Co^III species [pK _OH = 3.26(2)] and both these species react with the incoming ligand to form different ion associated species which react in the subsequent rate-determining steps (k ₁ and k ₂) to form presumably a ligand-substituted, mono-bridged species, [(nta)(OH)Co--OH-Co(nta)(L)]^2–. Values for k ₂, the preferred mono--hydroxo bridged substitution pathway for these reactions, vary between 6.8(2) × 10^–4 s^–1 (py) and 8.5(4) × 10^–2 s^–1 (dmap).     

Determination of oxaliplatin in human plasma and plasma ultrafiltrate by graphite-furnace atomic-absorption spectrometry

A method for sensitive determination of the anti-cancer agent oxaliplatin in human plasma and human plasma ultrafiltrate (pUF) is presented. The method is based on the quantification of platinum by graphite-furnace atomic-absorption spectrometry, with Zeeman correction and an atomisation temperature of 2,700°C. Sample pretreatment involves dilution of the samples with a solution containing 0.15 mol L^–1 NaCl and 0.20 mol L^–1 HCl in water. Validation was performed in accordance with the most recent FDA guidelines for bioanalytical method validation. All results were within requirements. The validated ranges of quantification were 0.10–400 mol L^–1 for human pUF and 0.50–400 mol L^–1 for plasma. The assay is now successfully used to support pharmacokinetic studies of cancer patients treated with oxaliplatin.     

Simultaneous Determination of Pioglitazone and Glimepiride by High-Performance Liquid Chromatography

A rapid and accurate HPLC method has been developed for simultaneous determination of pioglitazone and glimepiride. Chromatographic separation of the two pharmaceuticals was performed on a Cosmosil C₁₈ column (150 mm × 4.6 mm, 5 m) with a 45:35:20 (v/v) mixture of 0.01 m triammonium citrate (pH adjusted to 6.95 with orthophosphoric acid), acetonitrile, and methanol as mobile phase, at a flow rate of 1.0 mL min^–1, and detection at 228 nm. Separation was complete in less than 10 min. The method was validated for linearity, accuracy, precision, limit of quantitation, and robustness [1, 2]. Linearity, accuracy, and precision were found to be acceptable over the ranges 2.50–30.00 g mL^–1 for pioglitazone and 0.10–10.00 g mL^–1 for glimepiride.     

Alternative spectrophotometric determination of niobium and tantalum with o-hydroxyhydroquinonephthalein in cationic surfactant micellar media

Summary The alternative and simultaneous spectrophotometric determination of niobium and tantalum was examined by using the colour development between o-hydroxyhydroquinonephthalein (Qnph) and niobium or tantalum in the presence of hexadecyltrimethylammonium chloride (HTAC) in strong acidic media. Beer's law was obeyed up to 10.0 g of niobium and up to 18.0 g of tantalum in a final volume of 10.0 ml. The apparent molar absorption coefficients for niobium and tantalum were 2.18×10⁵ and 2.09×10⁵ l mol^–1 cm^–1 with Sandell's sensitivities of 0.00042 g/cm² niobium at 520 nm and 0.00085 g/cm² tantalum at 510 nm, respectively. The alternative assay of niobium and tantalum was possible by using two methods: Method A — masking method with oxalic acid, Method B — acid adjusting-method using 50% sulfuric acid. These methods were 2–6-times more sensitive than other methods.Application of xanthene derivatives in analytical chemistry. Part XC. Part LXXXIX see ref [1]     

High-Performance Liquid Chromatographic Assay of Zonisamide (1,2-benzisoxazole-3-methanesulfonamide) in Human Plasma using a Solid-Phase Extraction Technique

A selective and sensitive liquid chromatographic method was developed for the determination of zonisamide in small volumes of plasma. Zonisamide and the internal standard methyl 4-hydroxybenzoate were extracted from 0.2 mL of plasma with solid-phase extraction columns and eluted with methanol. Analysis of the extracts was performed on a Symmetry C₁₈ column with ultra-violet spectrophotometric detection. The calibration curve was linear over the concentration range of 0.05–5 g mL^–1 in plasma. Recoveries were reasonable for routine analyses; the limit of quantification was 0.05 g mL^–1 with a signal-to-noise ratio of 5. This method could be useful for the pharmacokinetic study of zonisamide in a limited volume of human plasma and for therapeutic drug monitoring.     

Determination of levodopa methyl ester and its metabolites in rat serum by CZE with amperometric detection

A reliable and reproducible method, capillary zone electrophoresis with amperometric detection (CZE–AD), has been developed for separation and quantification of levodopa methyl ester (LDME) and its biotransformation products levodopa (L-DOPA) and dopamine (DA) in rat serum. A carbon-disk electrode was used as working electrode. The optimum conditions for CZE detection were 50 mmol L^–1 phosphate solution at pH 7.0 as running buffer, 17 kV as separation voltage, 1.0 V (vs Ag/AgCl, 3.0 mol L^–1) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 2.4×10^–2 to 2.2 g mL^–1 for LDME, 2.9×10^–1 to 49.5 g mL^–1 for L-DOPA, and 1.4×10^–2 to 1.5 g mL^–1 for DA with correlation coefficients of 0.9997, 0.9994, and 0.9999, respectively. The detection limits for LDME, L-DOPA, and DA were 14.6, 98.0, and 9.7 ng mL^–1, respectively. Recoveries were 80.3% for LDME, 93.5% for L-DOPA, and 86.5% for DA. This method was applied to serum samples after intravenous injection of LDME and L-DOPA to rats.