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.     

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.     

Spectrophotometric determination of nitrite in environmental waters using column preconcentration on biphenyl

Column preconcentration methods have been established for the spectrophotometric determination of trace nitrite with sulfanilic acid (SA) orp-aminoacetophenone (AAP) as the diazotizable aromatic amine andN, N-dimethylaniline (DMA) or 1-aminonaphthalene (AN) as the coupling agent, using differention-pairs co-precipitated with biphenyl. Nitrite ion reacts with SA in the pH range 2.0–3.0 and AAP in the pH range 1.7–3.0 in HCl medium to form water-soluble colourless diazonium cations. These cations are subsequently coupled with DMA in the pH range 3.7–6.1 for the SA-DMA system and AN in the pH range 1.7–2.3 for the AAP-AN system to be retained on microcrystalline biphenyl packed in a column. The solid mass is dissolved out from the column with 5 ml of DMF and the absorbance is measured by a spectrophotometer at 420 nm for the SA-DMA system and at 517 nm for the AAP-AN system. The calibration was linear over the concentration ranges 0.3–6.0 g of nitrite in 5 ml of DMF solution (i.e., 0.02–0.40 g/ml in the sample solution) for the SA-DMA system and 0.5–7.0 g of nitrite in 5 ml of DMF solution (i.e., 0.03–0.47 g/ml in the sample solution) for the AAP-AN system. The molar absorptivity and Sandell's sensitivity were respectively 2.63 × 10⁴lmol^–1cm^–1 and 1.75 × 10^–3 g cm^–2 for SA-DMA and 3.28 × 10⁴lmol^–1 cm^–1 and 1.40 × 10^–3 g cm^–2 for AAP-AN. The concentration factors were 4 and 16 for SA-DMA and AAP-AN, respectively. The detection limits were 0.0138 and 0.0175 g/ml NO₂ ^– for SA-DMA and AAP-AN, respectively. Seven replicate determinations of a solution containing 3.5 g of nitrite gave mean absorbances of 0.410 and 0.500 with relative standard deviations of 0.51 and 0.55% for SA-DMA and AAP-AN, respectively. Interference from various foreign ions has been studied and the methods have been applied to the determination of nitrite in environmental samples.     

Analysis of the Aerial Parts of Verbena officinalis L. by Micellar Electrokinetic Capillary Chromatography

A micellar electrokinetic capillary chromatography (MECC) method was developed for the qualitative and quantitative determination of five marker compounds (iridoid glycosides, flavonoids and phenylethanoids) in Verbena officinalis. Optimum separation was achieved using a 50 mM sodium borate solution (pH 9.3), containing 50 mM sodium dodecylsulfate (SDS) as surfactant, at an applied voltage of 25 kV and a temperature of 30 °C, respectively. Because of their different absorption maxima, the compounds were detected either at 205 or 235 nm. Calibration data confirmed linearity of the detector response within the concentration range injected (R² from 0.997 to 0.999), and revealed detection limits ranging from 5.0 g mL^–1 (verbascoside) to 13.6 g mL^–1 (hastatoside). The five markers were readily assignable in several samples of Verbena.     

Determination of nitrogen in uranium and uranium-oxide by high-temperature gas-extraction

Summary The reducing fusion gas extraction method has been used for the determination of nitrogen in uranium metal and uranium dioxide reference materials at levels of about 10–15g·g^–1. It has been found that when extracting at temperatures above 2700° C the use of a platinum flux is no longer necessary. Pure nitrogen and nitrogen-helium mixtures were used for calibrating the detection unit in the range of 1.5–670 g. The calibration of the extraction was performed with metallic reference materials in the range of 8–331 g N₂ content.

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Bestimmung von Stickstoff in Uran und Uranoxid durch Hochtemperatur-Gasextraktion

Zusammenfassung Die Gasextraktion aus reduzierender Schmelze wurde zur Stickstoffbestimmung in Uranmetall- und Urandioxid-Referenzmaterialien bei Gehalten von 10–15 g·g^–1 angewendet. Bei Temperaturen über 2700° C ist kein Platinbad mehr erforderlich. Zur Eichung der Detektionseinheit im Bereich von 1,5–670 g wurden reiner Stickstoff oder Stickstoff-Helium-Mischungen benutzt. Zur Eichung der Extraktion wurden metallische Referenzmaterialien mit (8–331g) N₂ eingesetzt.

     

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 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.     

Determination and Differentiation of Two Seemingly Identical Medicinal Herbs by Capillary Electrophoresis with Electrochemical Detection

A high-performance capillary electrophoresis with electrochemical detection (CE-ED) method has been employed for the determination of six bioactive ingredients in traditional Chinese herbs, Herba cepbalanoplosis segeti and Herba cirsii japonici. The effects of several factors such as the acidity and concentration of running buffer, the separation voltage, the applied potential and the injection time on CE-ED were investigated. Under the optimum conditions, the six analytes could be well separated within 21 min in a 75 cm length capillary at the separation voltage of 15 kV in a 50 mmol L^–1 borax running buffer (pH 8.4). A 300 m diameter carbon disk electrode was used as the working electrode positioned carefully opposite the outlet of the capillary in a wall-jet configuration at potential of +950 mV (vs. SCE). Good linear relationship was established between peak current and concentration of analytes over two orders of magnitude with detection limits (S/N=3) ranged from 1.5×10^–7 to 6.0×10^–7 g mL^–1 for all six analytes. This proposed method has been successfully applied for the analysis of traditional Chinese herbs after a relatively simple extraction procedure, further on, for the differentiation of these above two seemingly identical herbs based on their electropherograms or characteristic electrochemical profiles.     

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.     

Tris(2-ethylhexyl)phosphate as an extractant for quadrivalent tin,with subsequent determination with pyrocatechol violet in alloy samples

The solvent extraction of tin(IV) from chloride media withtris(2-ethylhexyl)phosphate is presented. Tin(IV) is extracted quantitatively from 2.75–3.20 mol dm^–3 hydrochloric acid using 6.38–6.91 mol dm^–3 tris(2-ethyl-hexyl)phosphate dissolved in toluene as an extractant. After back-extraction of tin(IV) with water from thetris(2-ethylhexyl)phosphate phase, it is estimated spectrophotometrically following complexation with pyrocatechol violet. The recommended range for determination of tin(IV) is 10–100 g. The probable extracted species is SnCl₄·2TEHP. The method is applicable to the analysis of alloy samples with a detection limit of 0.4 g/ml (for 10 g of tin) and a relative standard deviation between 0.21–0.32%.     

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 dextromethorphan and dextrorphan in urine by capillary zone electrophoresis: Application to the determination of debrisoquin-oxidation metabolic phenotype

Summary A capillary zone electrophoresis method has been developed for the determination of dextromethorphan and its metabolite, dextrorphan, in urine. A linear relationship was observed between the peak area and the concentration of both dextromethorphan and dextrorphan within the range of 490 ng mL^–1 to 500 g mL^–1 with a correlation coefficient of greater than 0.9999. The limit of detection was 80 ng mL^–1 for both compounds. The inter-day coefficients of variation for the concentrations of 2.5 g mL^–1 and 50 g mL^–1 were 6.2% and 4.1% for dextromethorphan, and 5.6% and 2.8% for dextrorphan (n=15). The method could be applied directly to the determination of dextromethorphan and dextrorphan in human urine without any sample pretreatment for the elimination of interfering compounds as is required in published highperformance liquid chromatography and gas chromatography methods. Using dextromethorphan as a probe of the debrisoquin-oxidation metabolic phenotype, the 44 healthy volunteers were phenotyped after oral administration of a 15 mg dose using both this capillary electrophoresis method and a high-performance liquid chromatography assay from the literature. Good agreement was found between the two methods.     

Chromotropic acid,a fluorogenic chelating agent for aluminium(III)

Complexation of aluminium(III) with the fluorogenic ligand chromotropic acid (4,5-dihydroxynaphthalene-2,7-disulfonic acid) has been revisited with the aim of using enhancement of the fluorescence intensity as an analytical tool. Complexation at the optimum pH4 was shown to lead to a 1:1 complex with a stability constant log ₁₁₀=18.4±0.7. The fluorogenic effect was thoroughly investigated. Nearly selective excitation of the chelate rather than the ligand could be achieved at wavelengths longer than 360 nm. For analytical purposes the main interfering ion was Ga³⁺. The strongest competing ligand was shown to be citric acid. Competitive complexation by acetate or formate ions can also make their use in a buffer at the usual concentration, 0.2 mol L^–1, questionable, whereas a 10^–2 mol L^–1 formic acid buffer was shown to be a good alternative. The calibration plot showed that the dependence of response on Al(III) concentration was linear up to 500 g L^–1; the detection limit was 0.65 g L^–1 (3SD _blank, n=10, SD=±1.4% at 10 g L^–1 and ±0.8% at 100 g L^–1). The analytical procedure was successfully applied to several samples of tap water and the results were in good agreement with those from AAS determination.     

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.     

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.     

Flow injection chemiluminescence determination of l-cysteine in amino acid mixture and human urine with the BrO3 −–quinine system

In this paper, a novel flow injection chemiluminescence (CL) determination of l-cysteine is proposed. The method is based on the CL reaction of l-cysteine and KBrO₃ in acidic medium. The CL intensity was greatly enhanced in the presence of quinine. The CL intensity was linear with l-cysteine concentration in the range of 0.2–80 g L^–1, and the detection limit was 0.1 g L^–1 (3). A complete analysis, including sampling and injecting, could be performed in 1 min, giving a throughput of about 60 h^–1. The relative standard deviation was 1.6% for 0.8 g L^–1 l-cysteine (n=11). The proposed method was satisfactorily applied to the determination of cysteine in an amino acid mixture and human urine. The mechanism of the CL reaction is also discussed.     

Direct analysis of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders by total reflection X-ray fluorescence spectrometry

A direct analysis procedure for the determination of trace impurities of Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga in Al₂O₃ ceramic powders by total reflection X-ray fluorescence spectrometry (TXRF) is described. The powders were analysed in the form of slurries containing 1–10 mg mL^–1 of powder. The use of the procedure in the case of powders with differing grain size and for different slurry concentrations was investigated. Three different quantification possibilities were compared, namely the use of Al as a matrix component, the use of Fe as a trace element contained in the sample or of Co added in concentrations of 200 g g^–1 as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 L of the 10 mg mL^–1 slurries was studied by scanning the 4- to 5-mm-diameter spots of two samples by synchrotron radiation TXRF at Hasylab. For powders with differing graininess but mainly finer than about a few 10 m, no systematic influence of the grain size on the accuracy of the determinations of Ca, V, Fe, Ni, Cu and Zn could be observed. The measurement precision, however, seemed to be limited by inhomogeneous distributions of the trace elements in the samples as testified by the synchrotron radiation TXRF scans. Detection limits of the developed TXRF procedure for Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga were found to be in the 0.3–7 g g^–1 range and were shown to increase slightly with the grain size of the samples. Quantification using Al (matrix) as internal standard led to systematically higher values out of the accuracy required, whereas the other two approaches in all cases led to reliable results.Dedicated to the memory of Wilhelm Fresenius     

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.     

Solid-phase reactor flow-injection on-line oxidizing spectrofluorimetry for determination and dissolution studies of folic acid

A simple, sensitive and specific flow-injection spectrofluorimetric method has been developed for the determination of folic acid in pharmaceuticals. The method is based on use of a lead dioxide solid-phase reactor for on-line oxidation of folic acid into a strongly fluorescent compound with a maximum excitation wavelength of 281 nm and an emission wavelength of 450 nm. Under optimum conditions the fluorescence intensity of oxidation product is proportional to the concentration of folic acid over the range 0.008–2.5 g mL^–1. The detection limit is 0.0001 g mL^–1, the relative standard deviation is 0.85% for 11 replicate determinations of 0.05 g mL^–1 folic acid, and the sample throughput is 20 h^–1. In combination with an on-line filter and dilution, an automated drug-dissolution system was established. The proposed method has been successfully applied to the determination of folic acid in pharmaceutical preparations and dissolution testing.