Chromatofocusing of paracetamol-containing pharmaceuticals on reversed-phase sorbents

The chromatofocusing technique has been applied for the formation of ascending linear and quasilinear pH gradients within columns with reversed-phase sorbents Diasorb D-130-C₁₈ and Diasorb-100-CN-mono for the first time. It was found that the optimum composition of mobile phases was 25 mM KH₂PO₄ + 25% CH₃CN (pH 3.0) for the starting solution and 3.15 mM KH₂PO₄ + 25% CH₃CN (pH 6.8–7.0) for the eluent. Separation of components of Maxicold and Efferalgan-C pharmaceuticals has been carried out by the chromatofocusing technique on the Diasorb-100-CN-mono sorbent.     

Excess Adsorption of Organic Eluent Components from Mobile Phases Containing Electrolytes

The excess adsorption isotherms of organic eluent components from solutions containing electrolytes on a C18-bonded stationary phase are investigated by frontal analysis in staircase mode. The excess adsorption of acetonitrile increases when NaHSO₄, NaH₂PO₄, NaCl, or NaOAc is added to the eluent, but decreases upon addition of NaBr or NaClO₄. The excess adsorption of acetonitrile increases in the order of NaCl, NaHSO₄, NaH₂PO₄?>?NaOAc?>?NaBr, NaClO₄. On the other hand, the effect of electrolyte addition on the excess adsorption of methanol is not significant. The effect of electrolytes on the retention of alkylbenzenes in reversed-phase liquid chromatography is discussed on the basis of the excess adsorption of organic eluent components. The retention of alkylbenzenes shows negative correlation with the excess adsorption of acetonitrile. This indicates that the acetonitrile layer on the stationary phase does not act as a part of the stationary phase. A developed acetonitrile layer reduces the retention of alkylbenzenes by the competitive adsorption at the interface between the organic layer and the stationary phase.     

Usefulness of chaotropic salt additive in RP‐HPLC of organic nonionized compounds

New synthesized 1,4‐disubstituted thiosemicarbazide derivatives were analyzed in the RP system, modified with the addition of salts; chaotropic (sodium hexafluorophosphate – Na PF₆), cosmotropic (sodium phosphate – NaH₂PO₄), and neutral (NaCl) on Zorbax XDB C18 column. The effect of the eluent composition on the analytes retention (k), system efficiency (N), peak symmetry (A_s), and LOD values were all examined and compared to unmodified organic‐aqueous mobile phase system. It was established that eluent modified with chaotropic salts addition was also the most advantageous according to other peak parameters such as the theoretical plates numbers and asymmetry factors. The lower LOD values were achieved in comparison to unmodified organic‐aqueous eluent system. Compatibility of lipophilicity parameters calculated by the use of computer software with experimental ones measured by RP‐HPLC was also the best for chaotropic modified mobile phase. To explain the observed phenomena, molecular modeling was performed for chosen representative compound in different environment representing examined mobile phase composition.     

Quantitative Separation of Volatile Fatty Acids by High-Pressure Liquid Chromatography

Abstract

Volatile fatty acids (acetic, propionic, butyric, isovaleric, and valeric) are separated isocratically on a reverse phase C₁₈ μBONDAPAK column in less than 20 min. The eluent was 0.01 M NaH₂PO₄ buffer, pH 3.5, containing 10% methanol. Separations were monitored by UV absorption at 210 nm. Peak height measurements gave quantitative linear responses from 0.25 μmole to 2.50 μmole of each acid.     

Simple eluents for the formation of ascending pH gradients in chromatofocusing of bipolar compounds

The formation of ascending pH gradients was studied in carboxyl columns with the use of eluents of simple composition (one or two components). The obtained gradients are comparable in a wide pH range with the gradient formed with the use of the synthetic polyampholytic eluent Polybuffer-96. The smoothest nearly linear pH gradients are formed at the ionic strength 0.05–0.5 in one or both mobile phases: the starting solution and the eluent. Potentialities of the analytical use of simple eluents in chromatofocusing were demonstrated with the example of the separation of a model mixture of proteins and formate dehydrogenase isoforms.     

Monitoring the Supercritical Fluid Extraction of Pyrethroid Pesticides using Capillary Electrochromatography

Capillary electrochromatography (CEC) is reported for monitoring the extraction of the pyrethroid pesticides fenpropathrin, fenvalerate and fluvalinate by SFE using supercritical CO₂. The optimum SFE conditions obtained for the pyrethroid pesticides from spiked cellulose matrix, were for fenpropathrin 300 atm and 70°C, fenvalerate 300 atm and 60°C and for fluvalinate 200 atm and 75°C. Extracts collected in methanol were subjected to analysis by CEC on a 30 cm × 75 μm i.d. fused silica capillary packed with 5 μm Hypersil ODS (21 cm packed length). Electrochromatograms of the three pyrethroid pesticides were obtained in order of elution thiourea (as the EOF marker), fenpropathrin, fenvalerate and fluvalinate, with mobile phase ACN-25 mM NaH₂PO₄ pH 8.3 (85 : 15), voltage 25 kV, electrokinetic injection 5 kV, 3 sec and detection at 200 nm. The SFE recoveries were > 80% for all three solutes. In addition, enantioseparation of the pyrethroid pesticides was investigated using Me-β-CD and HP-β-CD as chiral additives. The enantioseparation of fenpropathrin was optimised to a methanol-25 mM Tris pH 8.3 mobile phase (75 : 25) containing 70 mM Me-β-CD.     

Validated Optimized Method for Simultaneous Analysis of Active Silymarin Components and Dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethylene Dioxybiphenyl-2,2′-dicarboxylate in a Pharmaceutical Preparation by Use of a Monolithic Silica C18 Column

A simple, rapid, and sensitive isocratic reversed-phase LC method using a monolithic column has been developed and validated for simultaneous analysis of the active components of silymarin [taxifolin, silydianin, silychristin, diastereomers of silybin (silybin A and B), and diastereomers of isosilybin (isosilybin A and B)] and dimethyl-4,4′-dimethoxy-5,6,5′,6′-dimethylene dioxybiphenyl-2,2′-dicarboxylate in a commercial formulation. The mobile phase was a 45:55 (v/v) mixture of methanol and 5 mM NaH₂PO₄ (adjusted to pH 2.75 with phosphoric acid) at a flow rate of 1.5 mL min^?1. UV detection was performed at 288 nm and quantification was based on peak area. The method was validated for linearity, accuracy, precision, selectivity, and robustness.     

Direct chiral separation of caderofloxacin enantiomers by HPLC using a glycoprotein column

The enantiomers of caderoflxacin (CS-940), the new antibacterial fluoroquinolone compound, were separated on the commercially available α-acid glycoprotein-coated chiral stationary phase (Chiral-AGP) using the mobile phase of IPA: 0.15 M NaH₂PO₄ + Et₃N (pH 7.9) = 3: 97 at 0.8 mL/min with UV detection at 282 nm. The chromatographic behavior of caderofloxacin enantiomers was investigated by varying the mobile phase conditions. The chiral assay method was validated and used to determination of (R)-Caderofloxacin in (S)-Caderofloxacin raw material samples.     

A study of HPLC separation and spectrophotometric and voltammetric detection of 4′-substituted derivatives of 3-carboxy-4-hydroxy-6-acetylaminoazobenzene

 Optimised conditions have been found for the separation of 3-carboxy-4-hydroxy-6-acetylaminoazo-benzene derivatives substituted in the position 4′ (4′-R-CHAAB, where R=–H, –CH₃, –OCH₃, –Cl, –COCH₃, –NO₂ and –NHCOCH₃) using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of 0.01 mol/L NaH₂PO₄ at pH 4 with methanol (1+1), 0.01 mol/L NaH₂PO₄ at pH 2 with acetonitrile (1+1) or 1% aqueous acetic acid with methanol (4+6). UV photometry is the most universal detection technique and yields limits of detection around 10^-6 mol/L. Direct anodic voltammetry on a glassy carbon fibre array detector yields lower limits of detection for –COCH₃ derivatives and higher limits of detection for –NO₂ and –NHCOCH₃ derivatives. When the analytes are chemically reduced using zinc powder in acetic acid, the voltammetric detection has limits of detection one order of magnitude lower than those obtained UV photometrically. Received: 27 June 1996/Revised: 25 October 1996/Accepted: 3 November 1996     

Osmotic and activity coefficients of {yNaH2PO4+(1−y)Na2SO4}(aq) at the temperature 298.15 K

The osmotic coefficients of the mixed electrolyte solution {yNaH₂PO₄+(1−y)Na₂SO₄}(aq) have been measured by the isopiestic method, at the temperature T=298.15 K. The activity coefficients of NaH₂PO₄ and Na₂SO₄ were calculated by Scatchard's neutral-electrolyte method and by Pitzer and Kim's treatment for mixed-electrolyte solutions. The Scatchard interaction parameters are used for calculation of the excess Gibbs energy as a function of ionic strength and ionic-strength fraction of NaH₂PO₄. Also, the Zdanovskii's rule of linearity is tested.     

Quantitative analysis of Pentalgin tablets by gradient and isocratic high-performance liquid chromatography

The retention of paracetamol, propyphenazone, caffeine, phenobarbital, and codeine phosphate, which are the components of the new medicine Pentalgin, was studied by reversed-phase high-performance liquid chromatography on a column (150 × 3.9 mm) filled with the Symmetry C18 sorbent (5.0 μm) in the gradient elution mode and on a column (150 × 3.9 mm) filled with the Nova-Pak CN HP sorbent (4.0 μm) as a function of the profile and composition of the gradient and as a function of the concentrations of acetonitrile and KH₂PO₄ and the pH of the mobile phase, respectively, with detection at 212 nm. The optimum composition of the mobile phase was selected. The time of separation was 16 and 11 min for the gradient and isocratic elution modes, respectively. The procedures were used for the analysis of a preproduction sample of the tablets. The procedures provide accurate and reproducible results of analysis; however, the isocratic version is preferable for mass production control as a technically simpler technique.     

Prediction of the chromatographic behaviour for a series of diuretic compounds

Summary The proportion of organic modifier and the pH of the acetonitrile-water mixtures used as mobile phases were optimized in order to separate a group of diuretic compounds covering a wide range of physyco-chemical properties. The Linear Solvation Energy Relationship (LSER) formalism based either on the multiparameter π^*, β and α scales or the single solvent polarity parameterE _T ^N , have been used to predict their chromatographic behaviour as a function of the percentage of acetonitrile in the eluent. Moreover, correlation established between retention and pH of the aqueous-organic mobile phases have been used to predict the chromatographic behaviour of the diuretic compounds studied as a function of the eluent pH. Linear correlation between a function of the eluent pH. Linear correlation between the chromatographic retention and theE _T ^N polarity parameter of mobile phases containing different percentages of organic modifier has been obtained Based on the knowledge of the acid-base dissociation constant the relation between retention and mobile phase pH has also been linearized. These relationship allowed an important reduction of the experimental retention data needed for developing a given separation and a great improvement in chromatographic optimization schemes.     

Direct determination of chlorophenols present in liquid samples by using a supported liquid membrane coupled in-line with capillary electrophoresis equipment

Actually there is a great trend on the development of effective analytical methods for monitoring trace levels of various phenols which can indicate, among others compounds, the water quality. A simple, inexpensive supported liquid membrane (SLM) device was used in combination with commercially available capillary electrophoresis (CE) equipment for the direct determination of chlorophenols in surface water samples. The manifold was used simultaneously to extract and preconcentrate the analytes from liquid samples. In the extraction set-up, the donor phase (4 mL) was placed in the CE vial, where a micro-membrane extraction unit (MMEU) accommodating the acceptor phase (100 μL) in its lumen was immersed. The supported liquid membrane was constructed by impregnating a porous Fluoropore Teflon (PTFE) membrane with a water-immiscible organic solvent (dihexyl ether). The extraction process was optimized with regard to the pH of the donor and acceptor phases, membrane liquid, extraction time and voltage applied to the inlet or outlet vial during extraction. The chlorinated phenols pentachlorophenol (PCP), 2,3,6 trichlorophenol (TCP) and 2,6 dichlorophenol (DCP) were thus efficiently separated by CE, using tris(hydroxymethyl)aminomethane (Tris) and an NaH₂PO₄ solution containing 1% (v/v) methanol at pH 10.5 as running buffer.     

The separation of arsenic species in soils and plant tissues by anion-exchange chromatography with inductively coupled mass spectrometry using various mobile phases

Anion-exchange chromatography (Hamilton, PRP-X100) with inductively coupled plasma mass spectrometry (ICP-MS) is commonly used for the speciation of arsenic in environmental and biological samples. However, retentions for As species are frequently different because of the use of widely different mobile phases. In addition, chloride in matrices interferes with arsenic determination. In this study, we systematically investigated various mobile phases based on ammonium salts affecting arsenic retention to eliminate chloride interference chromatographically. Hence, various mobile phases based on ammonium salts, including NH₄H₂PO₄, NH₄HPO₄, NH₄Ac, NH₄HCO₃ and NH₄NO₃, were examined for reasonable resolution and to separate chloride from arsenic species. The best result was obtained with a mobile phase containing 30 mM NH₄H₂PO₄ at pH 5.6, where the separation of arsenic species, including arsenite [As(III)], arsenate [As(V)], dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA)], was achieved within 9 minutes with reasonable resolution and free of chloride interference at its high level (500 mg L^− 1). The detection limits for the arsenic species were in the range of 0.1-0.3 μg L^− 1 with a direct injection of sample without removing matrix. Finally, the proposed method was used for the determination of arsenic species in contaminated soil and plant tissues.     

Thermal decomposition of bisphenol A-based polyetherurethanes blown with pentane: Part II—Influence of the novel NaH2PO4/NaHSO4 flame retardant system

The thermal degradation process of ethoxylated bisphenol A (BPA) and oxyalkylenated 2,6-toluylenediamine-based polyurethane (PU) foams blown with pentane and flame retarded by novel NaH₂PO₄ and NaHSO₄ intumescent system (5:3, w/w) was studied by thermogravimetry coupled with mass spectrometry (TG–MS), thermogravimetry coupled with Fourier transform infrared spectroscopy (TG–FTIR), pyrolysis–gas chromatography coupled with mass spectrometry (Py/GC–MS) and diffuse reflectance Fourier transform spectroscopy (DRIFTS) methods. It has been found that NaH₂PO₄/NaHSO₄ system is active both at the initiation stage of PU decomposition as well as it catalyses cross-linking reactions that lead to enhanced char formation during degradation; both effects contribute to the overall flame retardation effect.     

Chemical processes in kaolin sintered with NaH2PO4

The results of experiments on application of NaH₂PO₄ as a binding agent for ceramic kaolin samples were presented. The experiments were carried out at temperatures of 973, 1073 and 1173 K and NiO and CoO additives were used as tempering agents. The parameters of the obtained samples with NaH₂PO₄ were compared with the samples compressed with water only. The materials of 3-4 times higher bending strength, lower water absorption as well decreased open porosity were prepared during these experiments. The binding function of the NaH₂PO₄ additive relies on creation of some compounds in reaction between the products of its condensation and products of kaolin decomposition. Finally a ceramic material of prospective properties was created. This revised version was published online in July 2006 with corrections to the Cover Date.     

Electroanalytical Determination of Some Phenolic Acids by High‐Performance Liquid Chromatography at Gold Electrodes

The electrochemical and amperometric behavior of a gold electrode was investigated towards the oxidation of several common phenolic acids in neutral phosphate solutions. Au electrodes show an appreciable stability and reproducibility of the amperometric signals by using a constant applied potential of 1.0 V vs. Ag/AgCl. Separations of selected phenolic acids using a reverse phase C₁₈ analytical column with a mobile phase containing 10 mM NaH₂PO₄ plus 10 mM Na₂HPO₄ (pH 7) and methanol as organic modifier, are achieved isocratically in less than 30 min. The detection limits at the level of nmol/L and linear ranges of four‐five orders of magnitude are generally achieved. The proposed chromatographic strategy coupled with the electrochemical detection at the Au electrode was successful tested for the quantitative determination of phenolic acids in beer, red wine and brandy with good sensitivity and recovery.     

多壁碳纳米管固相萃取净化-高效液相色谱法测定猪肉和鸡肉中的磺胺多残留

建立了多壁碳纳米管为吸附剂的固相萃取净化-高效液相色谱-紫外检测测定猪肉和鸡肉中多种磺胺类药物多残留的方法。样品采用乙腈提取,多壁碳纳米管固相萃取净化,NaH₂PO₄缓冲溶液（pH 5.5~6.0）溶解上样,5%（v/v）丙酮-正己烷淋洗,丙酮-二氯甲烷（1：1,v/v）洗脱。色谱分离以50 mmol/L NaH₂PO₄-乙腈（7：3,v/v）为流动相,方法的线性范围为0.01~1.00 mg/L,线性相关系数大于0.998,检出限（LOD）为0.003 mg/L,定量限（LOQ）为0.01 mg/L。在0.02~0.2 mg/kg添加范围内,9种磺胺类药物的回收率高于70%,RSD低于8%,表明多壁碳纳米管对磺胺类药物具有较强的吸附富集能力。该方法简便、准确可用于动物组织及产品中磺胺药物残留的检测。     

Semi‐preparative high‐speed counter‐current chromatography separation of alkaloids from embryo of the seed of Nelumbo nucifera Gaertn by pH‐gradient elution

A new high‐speed counter‐current chromatography method for semi‐preparative separation and purification of alkaloids from embryo of the seed of Nelumbo nucifera Gaertn was developed by using pH‐gradient elution mode. Diethyl ether was used as the stationary phase of the two‐phase solvent system and Na₂HPO₄/NaH₂PO₄ buffer solution with pH values of 7.5 and 7.2 in gradient mode as the mobile phase. Consequently, 33 mg of liensinine, 42 mg of isoliensinine, and 67 mg of neferine were obtained from 200 mg of crude extracts. The purities of them were all over 98% as determined by HPLC area normalization method, and the structures were identified by ¹H‐NMR and ¹³C‐NMR.     

Simultaneous analysis of six cardiovascular drugs by capillary electrophoresis coupled with electrochemical and electrochemiluminescence detection,using a chemometrical optimization approach

CE coupled with dual electrochemical (EC) and electrochemiluminescence (ECL) detection was optimized for simultaneous analysis of six cardiovascular drugs (alprenolol, propafenone, acebutolol, verapamil, atenolol and metoprolol) via central composite design. Following this study, three critical electrophoretic factors governing the CE separation were investigated: Tris‐H₃PO₄ buffer concentration, buffer pH value and separation voltage. A modified chromatographic response was adopted for evaluating CE separation quality. Optimum conditions were achieved using Tris‐H₃PO₄ buffer 35.6 mM (pH 2.3) separated at 13.9 kV, which was employed experimentally and led to the successful simultaneous separation of the above six drugs. The good agreement of the chromatographic response was observed between predicted data and actual experimental results using these optimized conditions (RSD=3.75%). The proposed method was validated for linearity, repeatability and sensitivity, and subsequently successfully applied to determine six basic drugs in urine samples.