Arsenic Speciation in Water by High-Performance Liquid Chromatography with Electrothermal Atomic Absorption Detection

A procedure was developed for determining arsenite, arsenate, monomethylarsonate, and dimethylarsinite ions in natural waters in concentrations 0.05–0.07 mg/L. The procedure involved separation by high-performance liquid chromatography and off-line determination by electrothermal atomic absorption spectrometry. The procedure was used to study arsenic transformations in the aquatic ecosystem of a tailing pit of an ore-dressing industrial plant.     

New Fluorimetric Detection Method of Corticosteroids after High-Performance Liquid Chromatography Using Post-Column Derivatization with Glycinamide

Abstract

Some biological corticosteroids were detected by a new fluorimetric method using post-column derivatization with glycinamide.

Urinary corticosteroids which are hydrolyzed and extracted from sample fluid are detected by the reaction with glycinamide in the presence of hexacyanoferrate (III) in weakly alkaline media of borate buffer solution of pH 9.8 at 90 [ddot]C for 5 min.

This method is highly sensitive and specific for some corticosteroids and the reaction is performed under mild condition, compared with the fluorimetric method using the reaction with sulfuric acid, so that this method can be used for fractional assay of urinary corticosteroids of patients for a steroid abnormal metabolism.     

Rapid and Sensitive Method for Citrinin Determination Using High-Performance Liquid Chromatography with Fluorescence Detection

Citrinin is a toxic product of secondary metabolism of fungi, such as certain Aspergillus, Penicillium, and Monascus species that are usually contaminating cereals. A new sensitive liquid chromatographic method with fluorescence detection was developed, validated, and applied for citrinin determination. The method is based on reversed-phase separation at pH 2.5, where citrinin exhibits the highest fluorescence quantum yield. In this setup, no derivatization step is needed. The method shows linearity in the range between 0.2 μg/mL and 0.1 mg/mL. The detection limit reached is 90 ng/mL (3.6 × 10^?7 M). Validated method was successfully applied on analysis of spiked and real cereal samples.     

Determination of Squalene Using High-Performance Liquid Chromatography with Diode Array Detection

A high-performance liquid chromatographic method with photodiode array detection has been developed for the determination of squalene. After treated by extraction and fractional crystallization, squalene was analyzed on a C₁₈ column (150 × 3.9 mm, 5 m) with acetonitrile as mobile phase. Excellent linearity of the calibration curve was observed in the range of 100–40000 gL^–1 and the detection limit was 40 gL^–1. The recoveries were from 89.6% to 100.5% and the relative standard deviations were from 0.5% to 1.4%. The method was successfully applied to the determination of squalene in squalene capsules, olive oil, algal lipids and algal cells.     

Determination of Reserpine in Plasma Using High-Performance Liquid Chromatography with Fluorescence Detection

Abstract

A high-performance liquid chromatographic method for determining reserpine in plasma has been developed. The procedure involves extraction of reserpine from buffered plasma into benzene, oxidation of reserpine to a fluorophor by treatment with vanadium pentoxide in phosphoric acid, and chromatographic separation of the reserpine fluorophor on an octadecylsilane column by ion-pairing with heptanesulfonate ions. Fluorescence monitoring of the column effluent provides high sensitivity of detection and increases the specificity of the procedure. A detection limit of approximately 100 pg of reserpine per ml of plasma was obtained following analysis of 2 ml samples. Analysis of a number of samples demonstrated the applicability of this method in confirming the presence of reserpine in equine plasma specimens collected at various horse shows and in evaluating the pharmacokinetic behavior of reserpine following intramuscular administration to horses.     

Determination of Sulfamerazine in River Water Using Thermoresponsive Modified Silica for Solid-Phase Extraction with High-Performance Liquid Chromatography Detection

Four thermoresponsive silica-poly(N-isopropylacrylamide-co-butyl methacrylate) materials were prepared by grafting (N-isopropylacrylamide-co-butyl methacrylate) at different ratios on multimodal porous silica via surface-initiated atom transfer radical polymerization. The thermoresponsive materials were employed as the adsorbent for the rapid determination of sulfamerazine in river water by solid-phase extraction. The properties of silica-poly(N-isopropylacrylamide-co-butyl methacrylate) were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Static adsorption measurements showed that the silica-poly(N-isopropylacrylamide-co-butyl methacrylate)₃ material had the highest adsorption characteristics (8.72?mg?g^?1) at 35°C. The solid-phase extraction conditions were optimized, including the elution solvent and its volume used. The thermoresponsive silica-poly(N-isopropylacrylamide-co-butyl methacrylate)₃ material provided satisfactory results for solid-phase extraction, with a recovery of 90.06%, allowing the rapid purification of sulfamerazine in river water.     

Catalytic Detection of Acetylthiourea in High-Performance Liquid Chromatography

The catalytic effect of substituted thioureas was found in the indicator reaction of the oxidation of Bromopyrogallol Red with bromate. Conditions of conducting the oxidation reaction of Bromopyrogallol Red with potassium bromate in the batch and dynamic modes were studied. The parameters of the flow system and the preconcentration of reactants were optimized. A technique was developed for the selective catalytic detection of acetylthiourea after its chromatographic separation from other thioureas, which allows its determination in the presence of 100-fold amounts of dimethylthiourea and ethylthiourea. The detection limit of acetylthiourea was 1 × 10^–5 M. The proposed technique can be used in pharmacology and medical practice.     

Micro-Scale Method for Determination of Tobramycin in Serum Using High-Performance Liquid Chromatography

Abstract

A rapid, simple, accurate, and micro-scale method for the determination of tobramycin, sisomicin and netilmicin in serum using high-performance liquid chromatography has been developed. The method is sensitive to 0.3 pg/ml using only 20 μl of serum. The serum is deproteinized with methanol containing an internal standard: sisomicin for the tobramycin, netilmicin for the sisomicin, and sisomicin for the netilmicin. After centrifugation, a counter-ion reagent is added to the supernatant, then an aliquot of the solution is injected into the chromatograph. Tobramycin, sisomicin and netilmicin are separated by reversed-phase, ion-pair chromatography and detected by fluorescence using continuous-flow, post-column derivatization with o-phthalaldehyde. For the tobramycin, within-run and day-to-day variation was below 2.5%. Correlation of this method with microbiological assay and homogeneous enzyme immunoassay was good.     

Derivatization of Ketosteroids for High-Performance Liquid Chromatography with Electrochemical Detection

Abstract

A highly sensitive and selective derivatization of ketosteroids for use in high-performance liquid chromatography with electrochemical detection (HPLC/EC) is described. When the detector response for three phenylhydrazone derivatives was compared with one another using dehydroepiandrosterone, the p-nitrophenylhydrazone showed the highest sensitivity with a detection limit of 200 pg. Dehydroepiandrosterone and other principal 17-ketosteroids in human blood were quantitatively derivatized into p-nitrophenylhydrazones and efficiently separated by HPLC/EC on a μBondapak C_{1 8} column using 0.5%. NH₄H₂PO₄/methanol (2:7, v/v).     

Separation of Minute Quantities of Impurities in Nonapeptides by Reverse-Phase High-Performance Liquid Chromatography: Critical Nature of The Water/Acetonitrile Ratio

Abstract

A detailed study of the influence of the eluent composition, such as the ratio of the concentration of water to acetonitrile and the apparent pH, for the analysis of nonapeptides by high-performance liquid chromatography is described. Selection of the optimum conditions is based on maximizing the separation of the minor components from the major component in a minimum elution time.

This investigation also describes the effect of an elution gradient, the wavelength setting for the absorbance detection, recycling the main component through the column and using microparticulate octadecyl columns from different manufacturers.     

Determination of Tetracyclines in Water Samples Using Liquid Chromatography with Fluorimetric Detection

A liquid chromatographic method with fluorimetric detection is proposed for the determination of trace levels of oxytetracycline, tetracycline, chlortetracycline and doxycycline in water samples. The analytes are preconcentrated by solid phase extraction using reversed phase polymeric cartridges and acetonitrile as eluent. Preconcentration factors up to 125 can be obtained. The chromatographic separation is performed on a polymeric column with a gradient elution program using mobile phases based on mixtures of acetonitrile and 0.01 mol L^?1 oxalic acid aqueous solution at a flow rate of 1.2 mL min^?1. Tetracyclines are post-column derivatized with a reagent solution consisting of 0.1 mol L^?1 Mg(II) at pH 9 at a flow rate of 0.6 mL min^?1. The highly fluorescent Mg(II) chelates are detected at λ _ex = 374 nm and λ _em = 499 nm. The detection limits of the whole process are in the low μg L^?1 level. The proposed method has been applied to the analysis of spiked natural water samples, and recovery rates higher than 80% have been obtained.     

Determination of Amino Acids by High-Performance Liquid Chromatography with Electrochemical Detection Using Ferrocene Derivatization Reagents

Abstract

Two new reagents possessing ferrocene as an electrophore and isothiocyanate reactive toward the amino group were prepared and evaluated for pre-column derivatization of amino acids in high-performance liquid chromatography with electrochemical detection. The utilities of these reagents were investigated employing glycine as a model compound. Ferrocenylisothiocyanate was more favorable with respect to reactivity and electrochemical properties. The newly developed method was applied to the determination of 4-aminobutyric acid in biological specimens.     

Quantitation of Baclofen in Tablets Using High-Performance Liquid Chromatography

Abstract

A reverse phase high-performance liquid chromatography method has been developed to quantify baclofen in tablets. The method is accurate and precise with a percent relative standard deviation of 0.52 based on 5 readings. The recovery from the synthetic mixtures was quantitative. The results were in excellent agreement with the USP-NF colorimetric method. The method can be used to test the content uniformity of the tablets. Samples which were treated with either sulfuric acid or sodium hydroxide and boiled for 10 minutes did not show new peaks in the chromatogram. Baclofen appears to be a very stable compound.     

Determination of Tetracyclines in Honey Using Liquid Chromatography with Ultraviolet Absorbance Detection and Residue Confirmation by Mass Spectrometry

A determination method has been optimized and validated for the simultaneous analysis of tetracycline （TC）, oxytetracycline （OTC）, chlortetracycline （CTC） and doxycycline （DC） in honey. Tetracyclines （TCs） were removed from honey samples by chelation with metal ions bound to small Chelating Sepharose Fast Flow columns and eluted with Na2EDTA-Mcllvaine pH 4.0 buffers. Extracts were further cleaned up by Oasis HLB solid-phase extraction （SPE）, while other solid-phase extraction cartridges were compared. Chromatographic separation was achieved using a polar end-capped C 18 column with an isocratic mobile phase consisting of oxalic acid, acetonitrile and methanol. LC with ultraviolet absorbance at 355 nm resulted in the quantitation of all four tetracycline residues from honey samples fortified at 15, 50, and 100 ng/g, with liner ranges for tetracyclines of 0.05 to 2 μg/mL. Mean recoveries for tetracyclines were greater than 50% with R.S.D. values less than 10% （n= 18）. Detection limits of 5, 5, 10, 10 ng/g for oxytetracycline, tetracycline, chlortetracycline and doxycycline, respectively and quantitation limits of 15 ng/g for all the four tetracyclines were determined. Direct confirmation of the four residues in honey （2-50 ng/g） was realized by liquid chromatography-tandem mass spectrometry （LC/MS/MS）. The linear ranges of tetracyclines determined by LC/MS/MS were between 5 to 300 ng/mL, with the linear correlation coefficient r〉 0.995. The limits of detection of 1 to 2 ng/g were obtained for the analysis of the TCs in honey.     

小波变换用于高效液相色谱的基线校正

本文根据小波变换将信号分频的性质，用Ｄａｕｂｅｃｈｉｅｓ小波成功地解决了高效液相色谱中基线校正问题，用于定量分析乳酸－稀土络合物体系中的十六个稀土元素，所得结果与仪器给出了结果进行比较，准确度提高，重现性良好。     

Determination of Fatty Acids by High-Performance Liquid Chromatography with Electrochemical Detection Using A Ferrocene Derivatization Reagent

Abstract

New derivatization method using ferrocene reagents has been developed for the determination of fatty acids by high-performance liquid chromatography with electrochemical detection. Condensation of fatty acids with 3-bromoacetyl-1, 1'-dimethyl-ferrocene was effected in the presence of 18-crown-6 and potassium fluoride. The resulting esters showed the satisfactory sensitivity at +0.60 V vs. an Ag/AgCl reference electrode with a detection limit of 0.5 pmole. Also the high selectivity was obtained by using a twin electrode electrochemical detector. The proposed derivatization method was found applicable to the determination of fatty acids in human serum.     

Determination of Nitidine Chloride in Toothpaste by Dual Gradient Two-Dimensional High-Performance Liquid Chromatography

Nitidine chloride in toothpaste was determined by two-dimensional high-performance liquid chromatography. One gradient pump was used to enrich and purify the sample. The analyte was passed into the analytical column by switching a valve following the removal of the sample matrix. The samples were extracted by ultrasonic extraction. A C₁₈ (2.1 mm × 100 mm, 5 µm) column was used in one dimension, and a second C₁₈ (4.6 mm × 250 mm, 5 µm) column was used in the other dimension. The mobile phase was 0.02 mol/L monobasic potassium phosphate and acetonitrile with double isocratic elution. The wavelength of the ultraviolet-visible detector was 328 nm. The linear range for nitidine chloride was between 0.01 and 2 mg/L, with a correlation coefficient greater than 0.9998. The limit of detection for nitidine chloride was 0.01 mg/kg. The mean recoveries were 88.7% to 91.0%, and the relative standard deviation was less than 2.81%. This method is simple, sensitive, and accurate for the determination of nitidine chloride in toothpaste.     

A Method for the Determination of Methionine in Human Serum by High-Performance Liquid Chromatography with Electrochemical Detection

Abstract

We have found remarkable enhancement of electrochemical response for the analysis of methionine by use of a glassy carbon electrode preanodized in a 0.2 M phosphate buffer (KH₂PO₄?KOH, pH 6.5) at +1.9 V vs. Ag/AgCl for 2 min. On the basis of this finding, we have developed a method for the determination of methionine in human serum by reversed-phase high-performance liquid chromatography with electrochemical detection using the electrochemically pretreated glassy carbon electrode. The minimum detectable quantity of methionine has been found to be about 1 ng.     

Analysis of Triorganotin Compounds by High-Performance Liquid Chromatography with Reverse-Pulse Amperometric Detection

High-performance liquid chromatography (HPLC) coupled with the reverse-pulse amperometric (RPA) detection method has been developed for the analysis of triorganotin compounds in aqueous solutions. The major advantage of RPA vs. conventional amperometric detection is its ‘in situ’ elimination of interference from dissolved oxygen in the chromatographic eluent; therefore, no extra chemicals or apparatus are required for oxygen removal. With a Partisil-10 SCX column and an eluent of methanol/0.01 M sodium acetate buffer (70:30, pH 5.5), the four triorganotins, viz., trimethyl-, triethyl-, tripropyl-, and tributyltin, can be totally separated. Detection by RPA was performed with a static dropping mercury electrode with an initial potential of ?1.15 V and a final potential of +0.15 V. The absolute detection limit (S/N = 3) ranged from 12 ng of tributyltin (as tin) to 0.3 μg of trimethyltin (as tin). Applications of the method to the analysis of trace tributyltin in marine antifoulant leachate and sea water are described.