Determination of asymmetric and symmetric dimethylarginines in human plasma by HPLC with electrochemical detection

A new HPLC method was developed and validated for the determination of asymmetric and symmetric dimethylarginines and l ‐arginine in human plasma. After SPE and evaporation of the eluate, the samples were derivatised with an o‐phthaldialdehyde reagent containing 3‐mercaptopropionic acid. The derivatives formed were analysed by isocratic RP‐HPLC with electrochemical detection at +320 mV. The mobile phase consisted of 50 mM phosphate buffer (pH 6.1) containing 10% v/v acetonitrile, the flow rate was 1 mL/min. The retention times of all compounds including monomethylarginine (internal standard) were <24 min. The LODs (S/N 3:1) were 0.012 μM for both dimethylarginines and 0.013 μM for l ‐arginine; the linearity of the method was from 0.1 to 20 μM for both dimethylarginines and from 1 to 200 μM for l ‐arginine. Absolute extraction recoveries measured for all analytes ranged from 85 to 88%.     

HPLC of porphyrinogens with electrochemical detection

Summary A reversed-phase system is described for the separation of coproporphyrinogen I, II, III, IV isomers, deethylisocoproporphyrinogen and isocoproporphyrinogen. The porphyrinogens are detected electrochemically with high sensitivity. The relative retention of the prophyrinogens is mainly governed by the arrangement of the ethyl and methyl substituents around the macrocycle, although steric effect may also be an important parameter.     

Determination of hydrazine and 1,1-dimethylhydrazine as salicyldehyde derivates by liquid chromatography with electrochemical detection

Summary Determination of hydrazine and 1,1-dimethylhydrazine after derivatization with salicylaldehyde was done using high-performance liquid chromatography with electrochemical detection. The oxidation of the phenolic group of salicylaldazine (S-HY) and salicylaldehyde-1,1-dimethylhydrazone (S-UDMH) was optimized with respect to ionic strength, pH, and applied potential. Less than 5 ng of S-HY and S-UDMH could be detected. The detection limits for hydrazine and 1,1-dimethylhydrazine solutions were estimated to be 0.025 and 0.20 ppm, respectively.     

Determination of glibenclamide in human serum by HPLC

The antidiabetic drug glibenclamide can be reliably quantitated in human serum with high performance liquid chromatography. The serum is buffered and extracted with toluene. The organic solvent is evaporated, the residue dissolved in the mobile phase and an aliquot sampled automatically and chromatographed. UV-detection at 229 m allows a lower limit of quantitation of 5 ng/ml. Precise handling of exact volumes facilitates external calibration. Statistical data for imprecision and inaccuracy are given and illustrate reliable quantification. Application of the method to experimental and clinical pharmacokinetic studies with specific problems is illustrated.     

Separation and Determination of Methylnaltrexone in Human Plasma Samples After Oral Administration by HPLC Coupled with Electrochemical Detection

Introduction Opioidmedicationsarewidelyusedclinically forrelievingpainandasantidiarrhealsandantitus- sives.Opioidantagonistsconsistofagroupofnat- ural,semisynthetic,orsyntheticcompoundsacting onaseriesofreceptors.Concomitantwiththeabil- itytorelievepain,thesedrugshaveadverseef- fects.Side-effectsofopioidtreatmentincludenau- sea,constipation,urinaryretention,pruritus,fa- tigue,psychomimeticdisturbance,difficultmic- turition,vomitinganddependence.Thesesideef- fectsareoftensevereenoughtolimitthe…     

A review of post-column photochemical reaction systems coupled to electrochemical detection in HPLC

Post-column photochemical reaction systems have developed into a common approach for enhancing conventional methods of detection in HPLC. Photochemical reactions as a means of ‘derivatization’ have a significant number of advantages over chemical reaction-based methods, and a significant effort has been demonstrated to develop an efficient photochemical reactor. When coupled to electrochemical (EC) detection, the technique allows for the sensitive and selective determination of a variety of compounds (e.g., organic nitro explosives, beta-lactam antibiotics, sulfur-containing antibiotics, pesticides and insecticides). This review will focus on developments and methods using post-column photochemical reaction systems followed by EC detection in liquid chromatography. Papers are presented in chronological order to emphasize the evolution of the approach and continued importance of the application.     

Electrochemical,fluorescence, and UV detection for HPLC analysis of various cysteine derivatives

Electrochemical (ECD), fluorescence (FLD), and UV spectrophotometric (UVD) detection were used to monitor various S-alk(en)yl-L -cysteines and their corresponding sulfoxide isomers following pre-column derivatization with o-phthaldialdehyde-tert-butylthiol and separation by reversed-phase HPLC. Recording of hydrodynamic voltammograms, FLD stop-flow scanning, and on-line captured UV spectra were methods used for establishing optimal detector settings which were defined as a compromise between favorable selectivity and high sensitivity. Optimal detector settings were found at: (A) 750 mV vs. Ag/AgCl for ECD; (B) excitation at 230 nm and emission at 420 nm for FLD; and (C) 337 nm for UVD. Various aspects of detector practicability such as selectivity, baseline disturbances due to excessive reagent, scanning possibilities, as well as detection limits were evaluated and compared. Minimal detectable amounts of the compounds were in the range of 130-160 fmol for ECD, and 2.5-3.5 pmol and 13-16 pmol for FLD and UVD. In addition, the possibilities and benefits of detector coupling were examined.     

Development and optimization of a method for the analysis of Brazilein by HPLC with electrochemical detection

The aim of this study was to establish an easy and accurate method for the determination of Brazilein in plant samples due to its potential pharmacological activities. High-performance liquid chromatography (HPLC) with electrochemical detection (ED) was used for the assay of Brazilein in this study for the first time. Crucial influence parameters including concentration of dodecane-1-sulfonic acid sodium salt (DSASS), inorganic modifier, tetrabutyl-ammonium hydroxide solution (TBAOH), and applied potential of proposed method were investigated. The proposed method is simple, rapid (analysis time: approximately 10 min), sensitive [(detection limit: 0.6 ng per injection (20 microl) at a signal-noise ratio 3:1)], highly selective and precise (intra- and inter-day precisions were within 5%, n = 7). The calibration graph of Brazilein was linear in the range 0.6-150 ng per injection 20 microl. Recovery of Brazilein was over 92% by standard addition method.     

Determination of phenol in raw and potable waters by HPLC multi-electrode electrochemical detection

Summary A method is proposed for the determination of phenol in raw and potable waters using multi-electrode electrochemical detection HPLC. The coulometric efficiency of the electrochemical cell together with an ability to ‘screen out’ other electrochemically active species precludes the need for trace enrichment concentration techniques. The development work leading up to the proposed method is discussed with reference to selection of solvent pH and electrode potentials. The method has a limit of detection of 0.034μgl⁻¹ phenol and a total standard deviation of 0.083μgl⁻¹ phenol at a phenol concentration of 1.048μgl⁻¹ phenol in river water.     

HPLC with electrochemical detection of metal-flavonoid-complexes isolated from food

Summary The electrochemical and chromatographic behaviour of flavonoid standards and of flavonoids extracted from food (green tea, black tea and onions) is investigated with respect to metalbinding properties. It is shown that metals such as iron, copper or aluminium are complexed by flavonoids, preferrably by those having an aromatic o-dihydroxy structure. This is confirmed by cyclic voltammetry on HPLC fractions (stopped flow) and by AAS measurement of metals. As the complexing sites of flavonoids are closely related to electrochemical properties, this is used for an indirect detection of metal species at low oxidation potentials. For iron species in particular a sensitive and selective detection is possible. For copper reductive detection can also be used.     

Determination of sulphonamides in milk by HPLC with electrochemical detection

Summary A simple quantitative method for the analysis of the residues of sulphadiazine and sulphadimidine in milk is described. The method is based on a simple extraction step and high-performance liquid chromatography (HPLC) with electrochemical detection. The Chromatographic seperation is performed on a reversed phase column (RP-C2) and an aqueous eluent. With this analytical system 10 ng/ml can be detected. Recoveries of sulphonamides from milk are between 94.4% and 110% in the concentration range of 0.01–1.8 g/ml sample.

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Bestimmung von Sulfonamidrückständen in Milch mit Hilfe der HPLC und dem elektrochemischen Detektor

Zusammenfassung Es wird eine einfache Methode zum Nachweis von Sulfonamidrückständen in Milch am Beispiel von Sulfadiazin und Sulfadimidin beschrieben, mit der noch Rückstandsmengen von 10 ng/ml erfaßbar sind. Das Verfahren besteht aus einem einfachen Aufreinigungsschritt, der Trennung der Rückstände auf einer Umkehrphase (RP-C2) und der Detektion mit einem elektrochemischen Detektor. Die Wiederfindungsraten liegen zwischen 94,4% und 110% für einen Konzentrationsbereich von 0,01–1,8 g/ml Untersuchungsmaterial.

     

Determination of acetylcholine and choline in the femtomole range by means of HPLC,a post-column enzyme reactor,and electrochemical detection

Summary The measurement of choline and acetylcholine by means of HPLC, a post-column enzyme reactor, and electrochemical detection has been simplified and optimised. The use of a cation exchanger and enzyme reactor fitted in a cartridge holder appeared to result in reproducible, sensitive, and selective measurement of endogenous choline and acetylcholine with a lower detection limit of 50 fmole.     

The determination of serum retinol by high performance liquid chromatography

A method for the quantitation of retinol in serum by normal phase high performance liquid chromatography is described. The mobile phase consists of a hexane/diethylether/methanol mixture with spectrophotometric detection. The sample preparation is similar to that described by other authors and involves protein precipitation followed by extraction and direct injection onto the chromatograph. Adequate sensitivity is achieved using 200 μl samples. The internal standard chosen is α-naphthol because of its spectral similarities to retinol and its greater stability than the commonly used retinyl esters. The method has been successfully applied to the clinical evaluation of a number of malabsorption syndromes for which it is preferred to the measurement of total carotenoids.     

高效液相色谱法测定人血清中格列吡嗪浓度

建立了人血清中格列吡嗪浓度的HPLC测定方法, 为研究格列吡嗪的代谢动力学及相对生物利用度提供了方法. 采用Oasis HLB萃取小柱对血清样品进行处理, 格列齐特为内标, C18为固定相. 流动相为V(乙腈)∶V(0.08%三乙胺)＝40∶60水溶液;H3PO4 调节pH为3.5, 流速1.0 mL/min, 柱温30 ℃, 检测波长: 225 nm. 在12.5～1000 μg/L的质量浓度范围内, 格列吡嗪与内标峰的比值与质量浓度呈良好的线形关系(r=0.9959);格列吡嗪平均回收率为96.8%, 批间、批内RSD均小于6%, 检出限为12.5 μg/L (S/N≥3). 方法可用于药物代谢动力学及生物等效性的研究.