Nonaqueous capillary electrophoresis for the analysis of labile pharmaceutical compounds

Synthesis and characterization of a ZnMn2O4nanostructure as a chemical nanosensor: a facile and new approach for colorimetric determination of omeprazole and lansoprazole drugs

ZnMn₂O₄nanostructure was preparedviaan auto-combustion method using different fuels, and it was used as a chemical sensor for determination of omeprazole and lansoprazole drugs.

Non-aqueous microchip electrophoresis for characterization of lipid biomarkers

In vivo measurements of lipid biomarkers are hampered by their low solubility in aqueous solution, which limits the choices for molecular separations. Here, we introduce non-aqueous microchip electrophoretic separations of lipid mixtures performed in three-dimensional hybrid nanofluidic/microfluidic polymeric devices. Electrokinetic injection is used to reproducibly introduce discrete femtolitre to picolitre volumes of charged lipids into a separation microchannel containing low (100 μM-10 mM) concentration tetraalkylammonium tetraphenylborate background electrolyte (BGE) in N-methylformamide, supporting rapid electro-osmotic fluid flow in polydimethylsiloxane microchannels. The quality of the resulting electrophoretic separations depends on the voltage and timing of the injection pulse, the BGE concentration and the electric field strength. Injected volumes increase with longer injection pulse widths and higher injection pulse amplitudes. Separation efficiency, as measured by total plate number, N, increases with increasing electric field and with decreasing BGE concentration. Electrophoretic separations of binary and ternary lipid mixtures were achieved with high resolution (R s ∼ 5) and quality (N > 7.7 × 10(6) plates m(-1)). Rapid in vivo monitoring of lipid biomarkers requires high-quality separation and detection of lipids downstream of microdialysis sample collection, and the multilayered non-aqueous microfluidic devices studied here offer one possible avenue to swiftly process complex lipid samples. The resulting capability may make it possible to correlate oxidative stress with in vivo lipid biomarker levels.

A validated stability indicating HPLC method for the determination of process-related impurities in pantoprazole bulk drug and formulations

A stability-indicating high-performance liquid chromatographic (HPLC) method was developed with short run time and validated for the assay of process related impurities of pantoprazole in bulk form. Resolution of drug, its potential impurities and degradation products were achieved on a Hypersil ODS column utilizing a gradient with 0.01 M phosphate buffer of pH 7 and acetonitrile as eluent, at the detection wavelength of 290 nm. Flow rate was set at 1 mL min-1. The procedure was found to be specific, linear (r=0.999), recovery (97.9-103%), LOD (0.043-0.047 µgmL-1), LOQ (0.13-0.14 µgmL-1) and robust. Acceptable robustness indicates that the assay method remains unaffected by small but deliberate variations. Pantoprazole was found to degrade in acidic, oxidative and under photolytic stress conditions. The drug was stable to alkaline and dry heat conditions. This method has been successively applied to pharmaceutical formulation and no interference from the excipients was found.

Spectrophotometric determination of peptic ulcer sulfur-containing drugs in bulk form and in tablets

Two spectrophotometric procedures are suggested for the determination of three irreversible proton pump inhibitors, rabeprazole (RAB), omeprazole (OMP) and pantoprazole (PAN) in pure form and in different pharmaceutical formulations. The first method is based on the oxidation of RAB and PAN with potassium iodate in an acidic medium followed by extracting the liberated iodine with cyclohexane and measurement at λ = 520 nm. Beer's law is valid in the concentration ranges from 10-400 and 5-400 µg ml(-1) for RAB and PAN, respectively. The apparent molar absorptivities of the resulting coloured product were found to be 1.34 × 10(3) and 1.64 × 10(3) l.mol(-1). cm(-1) for RAB and PAN, respectively. The second method is based on the interaction of the basic drugs, OMP, RAB and PAN, in 1,2-dichloroethane with bromophenol blue (BPB), bromocresol green (BCG) and bromocresol purple (BCP) in the same solvent to produce stable coloured ion pairs with maximum absorbance at 385-405 nm. Regression analysis of Beer's plots showed good correlation in the concentration ranges 10-60, 10-60 and 5-40 µg ml(-1) for OMP, 10-150, 10-150 and 10-60 µg ml(-1) for RAB and 10-250, 10-150 and 10-100 µg ml(-1) for PAN with BPB, BCG and BCP reagents, respectively. The limits of detection are 0.46-7.69 µg ml(-1) and limits of quantitation range between 1.52-8.53 µg ml(-1). The optimum assay conditions were investigated and the recovery of the drugs from their dosage forms ranged from 99.33% to 100.5%. Intraday relative standard deviations (RSD) were 0.029-1.397% and the correlation coefficients ranged from 0.9992 to 1. The two methods can be applied successfully for the determination of these drugs in tablets. The results of analysis were validated statistically through recovery studies.

Analytical methodologies for the determination of omeprazole: An overview

Omeprazole, a gastric acid pump inhibitor, dose-dependently controls gastric acid secretion; the drug has greater antisecretory activity than histamine H(2)-receptor antagonists. Omeprazole has been determined in formulations and biological fluids by a variety of methods such as spectrophotometry, high-performance liquid chromatography with ultraviolet detection and liquid chromatography coupled with tandem mass spectrometry. The overview includes the most relevant analytical methodologies used in its determination since the origin still today.

Determination of omeprazole, hydroxyomeprazole and omeprazole sulfone using automated solid phase extraction and micellar electrokinetic capillary chromatography

A sensitive method for the determination of omeprazole and its metabolites has been developed. It involves an automated solid phase extraction (SPE) procedure and capillary electrophoresis with UV detection. Omeprazole, hydroxyomeprazole and omeprazole sulfone could be separated by micellar electrokinetic capillary chromatography using a background electrolyte composed of 20 mM borate buffer and 30 mM sodium dodecyl sulfate, pH 9.5. The isolation of omeprazole and its metabolites from plasma was automatically accomplished with an original SPE procedure using surface-modified styrene-divinylbenzene polymer cartridges. Good recovery data and satisfactory precision values were obtained. Responses were linear for the three analytes, from 0.08 to 2.0 microg/mL of plasma. Intra- and inter-day precision values of about 1.6% R.S.D. (n=10) and 2.5% R.S.D. (n=36), respectively, were obtained. The method is highly robust and no breakdown of the current or capillary blockages were observed during several weeks of operation. The validated method was applied to the determination of omeprazole in pharmaceutical preparations and for the analysis of plasma samples obtained from three volunteers who received oral doses of omeprazole.

Determination of omeprazole in rat plasma by high-performance liquid chromatography without solvent extraction

A HPLC method without solvent extraction and using ultraviolet detection at 302 nm for the determination of omeprazole in rat plasma has been validated. Plasma samples after pretreatment with acetonitrile to effect deproteinization were dried under N(2) at 40 degrees C and reconstituted with mobile phase. The standard calibration curve for omeprazole was linear (r(2)=0.9999) over the concentration range of 0.02-3 microgml(-1). The intra- and inter-day assay variability range was 4.8-9.2% and 5.2-10.3% individually. This method has been successfully applied to a pharmacokinetic study of omeprazole in rats.

Capillary electrophoresis inN,N-dimethylformamide

N,N-Dimethylformamide (DMF) is a dipolar protophilic solvent with physicochemical properties that makes it suitable as solvent for capillary electrophoresis (CE). It is prerequisite for the proper application of CE to adjust and to change the pH of the background electrolyte (BGE) in a defined manner. This was done in the present work using benzoic acid-benzoate by selecting different concentration ratios of acid and salt, and calculating the theoretical pH from the activity-corrected Henderson-Hasselbalch equation. The mobilities of the analytes (chloro- and nitro-substituted phenolates) were found to follow reasonably well the typical sigmoid mobility versus pH curve as predicted by theory. The actual mobilities and pK(a) values (at 25 degrees C) of the analytes were derived from these curves. pK(a) values were in the range of 11.1-11.7, being thus 3-4.4 units higher than in water. This pK(a) shift is caused by the destabilization of the analyte anion and the better stability (solubility) of the molecular analyte acid in DMF, which overcome the higher basicity of DMF compared to water. Absolute mobilities were calculated from the actual mobilities; they were between 32x10(-9) and 42x10(-9) m(2)/Vxs. Slight deviations of the measured mobilities from the theoretical mobility versus pH curve were discussed on the bases of ion pairing and heteroconjugation and homoconjugation of either buffer components or buffer components and analytes. Heteroconjugation was used as a mechanism for the electrically driven separation of neutral analyte molecules in a BGE where salicylate acted as complex forming ion. Rough estimation of the complexation constants for the phenolic analytes gave values in the range of 100-200 L/mol. Addition of water to the solvent decreased the effect of heteroconjugation, but it was still present up to the surprisingly high concentration of 20% water. Electrophoretically relevant parameters like ionic mobilities and pK(a) values, and conjugation and ion pairing are dependent on the water content of the solvent. The water uptake of DMF was measured when exposed to humidity of ambient air. The resulted behavior of the water uptake was found rather similar to that for acetonitrile and methanol.

Voltammetric behaviour of rabeprazole at a glassy carbon electrode and its determination in tablet dosage form

The oxidative behaviour of rabeprazole was studied at a glassy carbon electrode in Britton-Robinson (BR) buffer solutions using cyclic, linear sweep and differential-pulse voltammetry. The oxidation process was shown to be irreversible over the pH range (6.0-11.0) and was diffusion-adsorption controlled. An analytical method was developed for the determination of rabeprazole in BR buffer solution at pH 8.0 as supporting electrolyte. The anodic peak current varied linearly with rabeprazole concentration in the range 1.0 x 10(-6) to 2.0 x 10(-5) M of rabeprazole with a limit of detection of 4.0 x 10(-7) M. Validation parameters, such as sensitivity, accuracy, precision and recovery, were evaluated. The proposed method was applied to the determination of rabeprazole in the tablet dosage form. The results were compared with those obtained by a published high-performance liquid chromatographic method. No difference was found statistically.

Square-wave adsorptive cathodic stripping voltammetry of pantoprazole

Adsorption and reduction of pantoprazole were investigated by cyclic and square-wave voltammetry on a hanging mercury drop electrode in Britton-Robinson buffers at pH 2.0-11.0. The reduction process gave rise to a single peak within the entire pH range. Study of the variation of the reduction signal with solution variables such as pH and concentration of pantoprazole and instrumental variables such as accumulation time and potential, frequency, pulse height and pulse amplitude, has resulted in optimization of the reduction signal for analytical purposes. The voltammetric procedure was applied successfully to give a rapid and precise assay of pantoprazole in a tablet dosage form.

Determination of dissociation constants of labile drug compounds by capillary electrophoresis

The utility of capillary electrophoresis (CE) for determination of the negative logarithm of dissociation constants (pK(a)) of labile compounds was investigated. In this study pyridinyl-methyl-sulfinyl-benzimidazoles (PMSB's), which have both an acidic and a basic pK(a), were selected as a first set of model drug compounds. This is a group of compounds that are known to degrade in aqueous solutions under neutral and acidic conditions which thus may impair their pK(a) determination when using common batch techniques based on spectrophotometry or potentiometry. An additional set of model drug compounds, benzenesulfonic acid phenethyloxy-phenyl esters (BSAP's), which are labile at high pH, were also studied. It is demonstrated that pK(a) values can be determined with high precision and accuracy by CE for both these sets of model compounds because decomposition products and impurities can be sufficiently separated from the main component. Based on the results in this study, a general strategy is proposed and discussed for determination of pK(a) for labile compounds. Key steps comprise use of a stabilizing sample diluent, injection by electromigration, short analysis time, and characterization of the main component by UV-Vis spectra.

First-order UV-derivative spectrophotometry in the analysis of omeprazole and pantoprazole sodium salt and corresponding impurities

The first-order UV-derivative spectrophotometry, applying zero-crossing method was developed for the determination of omeprazole (OM), omeprazole sulphone (OMS), pantoprazole sodium salt (PANa), and N-methylpantoprazole (NPA) in methanol-ammonia 4.0% v/v, where the sufficient spectra resolutions of drug and corresponding impurity were obtained, using the amplitudes 1D(304), 1D(307), 1D(291.5) and 1D(296.5), respectively. Method showed good linearity in the ranges (microg ml(-1)): 1.61-17.2 for OM; 2.15-21.50 for OMS; 2.13-21.30 for PANa and 2.0-20.0 for NPA, accuracy and precision (repeatability and reproducibility). The experimentally determined values of LOD (microg ml(-1)) were 1.126; 0.76; 0.691 and 0.716 for OM, OMS, PANa and NPA, respectively. The obtained values of 2.91% w/w for OMS and 3.58% w/w for NPA in the presence of their parent drug, by applying the method of standard additions, point out the usage of the proposed method in stability studies. Zero-crossing method in the first-order derivative spectrophotometry showed the impurity-drug intermolecular interactions, due to the possible intermolecular hydrogen bonds, confirmed by divergences of experimentally obtained amplitudes for impurities OMS and NPA in comparison to expected values according to regression equations of calibration graphs.

Determination of pantoprazole by adsorptive stripping voltammetry at carbon paste electrode

A voltammetric method was described for the determination of pantoprazole by differential-pulse adsorptive stripping voltammetry at a carbon paste electrode. Accumulation of pantoprazole was found to be optimized in Britton-Robinson buffer (0.04 M, pH 4.0) solution following 5 min accumulation time at open circuit condition. Under optimized conditions, the current showed a linear dependence with concentration in the range 1.0 x 10(-7)-1.0 x 10(-5) M. The detection limit was 2.0 x 10(-8) M. The method was applied successfully for the analysis of pantoprazole in tablet dosage form. The results of accuracy and precision were comparable to those obtained by spectrophotometry.

Spectrophotometric and chromatographic determination of rabeprazole in presence of its degradation products

Three methods were presented for the determination of rabeprazole (RA) in presence of its degradation products. The first method was based on high performance liquid chromatographic (HPLC) separation of RA from its degradation products on a reversed phase, ODS column using a mobile phase of methanol-water (70:30, v/v) and UV detection at 284 nm. The second method was based on HPTLC separation followed by densitometric measurement of the spots at 284 nm. The separation was carried out on Merck HPTLC sheets of silica gel 60 F 254, using acetone-toluene-methanol (9:9:0.6 v/v) as mobile phase. The third method depends on first derivative of the ratio spectra (1DD) by measurement of the amplitudes at 310.2 nm. Moreover, the proposed HPLC method was utilized to investigate the kinetics of the oxidative and photo degradation processes. The pH-rate profile of degradation of RA in Britton-Robinson buffer solutions within the pH range 3-11 was studied. In addition, the activation energy of RA degradation was calculated in Britton-Robinson buffer solution pH 7.

Potential of formamide and N-methylformamide in nonaqueous capillary electrophoresis coupled to electrospray ionization mass spectrometry. Application to the analysis of beta-blockers

A nonaqueous capillary electrophoresis (NACE) method, coupled with either UV or electrospray mass spectrometry (ESI-MS), is described for the simultaneous analysis of seven beta-blockers. The same electrolyte, namely 25 mM ammonium formate and 1 M formic acid, was used with different investigated organic solvents. In addition to frequently used organic solvents such as methanol (MeOH) and acetonitrile (MeCN), formamide and its derivatives were investigated. Formamide (FA) and N-methylformamide (NMF) present several interesting physico-chemical properties, one of them being a high dielectric constant (e). Since FA and NMF possess a high UV cutoff, beta-blockers with an absorbance above 250 nm were selected as model compounds in order to compare NACE-UV and NACE-MS performances. FA and NMF showed different selectivity compared to water, MeOH or MeCN, and also demonstrated a higher efficiency in terms of the number of theoretical plates (especially NMF). To overcome their unfavorable optical properties, hyphenation with MS detection appears as a promising technique, thanks to its benefits in terms of selectivity, sensitivity and universality. The practical compatibility of FA and NMF with ESI-MS detection in combination with a sheath liquid configuration was demonstrated. In comparison to UV detection, sensitivity was increased, while a high efficiency was maintained. In addition, the low and stable generated currents observed were evidences for the successful hyphenation with ESI-MS. Hence, FA and NMF seemed to be promising alternatives in NACE-ESI-MS, either used as pure organic solvent or as a mixture with MeOH or MeCN.

Omeprazole determination using HPLC with coulometric detection

A sensitive high performance liquid chromatography (HPLC) method for the determination of omeprazole and three related benzimidazoles is reported. Coulometric detection was carried out at +800 mV using a porous carbon electrode. The linear range is 0.01-10 microg/ml. The method has a high degree of precision; the relative standard deviation of omeprazole at a concentration of 1.06 microg/ml was 0.7% (n=4). The cyclic voltammogram of omeprazole is consistent with the hydrodynamic voltammogram exhibiting a single major irreversible oxidative wave with a peak potential at +1105 mV. The response factors for the four compounds are similar indicating that the oxidative process does not involve the sulfur moiety exclusively. The data are most consistent with oxidation primarily of the benzimidazole groups. The method was applied successfully to the determination of omeprazole in a paste formulation.

Nonaqueous capillary electrophoresis: a versatile completion of electrophoretic separation techniques

Nonaqueous capillary electrophoresis (NACE) is the application of a conductive electrolyte dissolved in either one organic solvent or a mixture of several organic solvents to carry out zone electrophoresis or related techniques in fused-silica capillaries. A complete review on the fundamentals, the optimization of analytical methods, practical considerations, and applications is given. To explain the differences to CE in aqueous media, a brief summary on solvent properties and molecular interactions in solutions introduces the reader into these fields. The use of additives to tune separation selectivity by means beyond a pure zone-electrophoretic mechanism is discussed in detail for organic media. Special detection techniques providing high potential for NACE are presented. Data on the precision of NACE methods and a list of relevant applications are included. More specialized applications like the determination of physicochemical constants in NACE or the setup of a semipreparative mode are described.

Non-aqueous capillary electrophoresis

The benefits of non-aqueous capillary electrophoresis have been described in a number of recent publications. The wide selection of organic solvents, with their very different physicochemical properties, broadens our scope to manipulate separation selectivity. The lower currents present in non-aqueous solvents allow the use of high electric field strengths and wide bore capillaries, the latter in turn allowing larger sample load. In many cases detection sensitivity can also be enhanced. The potential of non-aqueous capillary electrophoresis is discussed throughout the paper, and the feasibility of capillary electrophoresis under non-aqueous media is demonstrated with reference to several applications.

Chiral separation of amino acids and peptides by capillary electrophoresis

Chiral separation of amino acids and peptides by capillary electrophoresis (CE) is reviewed regarding the separation principles of different approaches, advantages and limitations, chiral recognition mechanisms and applications. The direct approach details various chiral selectors with an emphasis on cyclodextrins and their derivatives, antibiotics and chiral surfactants as the chiral selectors. The indirect approach deals with various chiral reagents applied for diastereomer formation and types of separation media such as micelles and polymeric pseudo-stationary phases. Many derivatization reagents used for high sensitivity detection of amino acids and peptides are also discussed and their characteristics are summarized in tables. A large number of relevant examples is presented illustrating the current status of enantiomeric and diastereomeric separation of amino acids and peptides. Strategies to enhance the selectivity and optimize separation parameters by the application of experimental designs are described. The reversal of enantiomeric elution order and the effects of organic modifiers on the selectivity are illustrated in both direct and indirect methods. Some applications of chiral amino acid and peptide analysis, in particular, regarding the determination of trace enantiomeric impurities, are given. This review selects more than 200 articles published between 1988 and 1999.