Biomedical subjects

C Barbas

Publications and source records attributed to C Barbas.

At least 19 recordsLinked to original sources

PubMed2006

Chromatography-based on- and in-line pre-concentration methods in capillary electrophoresis.

Capillary electrophoresis (CE) poses unique challenges in many different analytical applications, mainly to biological and complex samples and when only small amounts of sample are available, due to its low sample consumption. As a consequence, poor limits of detection are usually observed with this technique, especially with UV photodetectors. Minimal or no sample treatment is desirable in any analytical method to avoid external sources of contamination or errors and to provide a high throughput. On- and in-capillary sample pre-concentration strategies, based on solid-phase extraction (SPE) technology can take advantage of both techniques (SPE and CE), while avoiding sample contamination and tedious manipulations when the sample amount is an issue. Moreover, the combination can provide two-dimensional separations. This review collects the most recent strategies that merge SPE technology built on- and in-capillary pre-concentration for increasing sensitivity and/or selectivity.

Chromatography↗

PubMed2006

Capillary electrophoresis for caffeine and pyroglutamate determination in coffees study of the in vivo effect on learning and locomotor activity in mice.

In a preliminary study pyroglutamate showed to be over 10 times increased in some lyophilised coffees with respect to brewed or filtered coffees, and probably that increase is related to some stage of the industrial process. Pyroglutamate is known to have a number of remarkable cognitive enhancing effects, which could be also related to the properties of coffee traditionally associated to caffeine. Pyroglutamate improves memory and learning and has anti-anxiety effects in rats. Therefore, a method has been developed and validated for the simultaneous determination of caffeine and pyroglutamate in coffee by capillary electrophoresis. Separation conditions employed MECK conditions with 50 mM borate buffer at pH 9.5 with 130 mM SDS. The applied potential was 10 kV and detection was performed at 200 nm. Afterwards, 10 soluble coffees from the market were measured and caffeine and pyroglutamate levels were compared. Those coffees with higher pyroglutamate with or without caffeine were preliminarily tested for sedative/stimulant properties and cognition enhancing effects in mice. The most relevant finding was a partial reversal of scopolamine-induced amnesia in the passive avoidance paradigm after oral administration of one coffee.

Animals↗

PubMed2005

Tandem column for the simultaneous determination of arginine, ibuprofen and related impurities by liquid chromatography.

Ibuprofen arginate is a rapidly absorbed salt designed to promote more rapid onset of analgesia than commercially available forms of ibuprofen. Ibuprofen and arginine have very different polarities and this becomes in a chromatographic problem, further complicated with the determination of related compounds, which is necessary in stability assays of the pharmaceutical forms. The common solution is the employment of two separate methods, but this is time consuming. A LC method has been developed to determinate both compounds and related impurities in one run. Ibuprofen, arginine and three ibuprofen related impurities (B, E and J) have been baseline separated with isocratic conditions at pH 3.0 and run time under 20 min by employing a tandem combination of two different stationary phases: first a ZORBAX SB-C18 column from Agilent (250 mm x 4.6 mm and 5 microm) and downstream a SUPELCOSIL LC-NH2 column from Supelco (150 mm x 4.6 mm and 3 microm). The octadecyldiisobutylsilane column provides the separation of ibuprofen and its impurities by a hydrophobic mechanism, whereas aminopropyl column offers selective retention of arginine by dipolar interaction mechanism. Method has been successfully validated following ICH guidelines and it has been demonstrated to be reliable for arginine, ibuprofen and related impurities determination in sachets of two different dosages as pharmaceutical forms. Moreover, stress test has proved the selectivity of the method for degradation products, such as those that can emerge throughout long-term stability assays.

Arginine↗

PubMed2005

Systematic comparison of different functionality columns for a classical pharmaceutical problem.

The performance of five reversed-phase columns which included a standard C18 phase, a polar embedded phase (amide group), a polyethyleneglycol phase, a cyano phase, and a perfluorinated phase, all coming from the same manufacturer, have been studied. They were systematically compared with a test mixture containing basic, neutral and acidic compounds of very different polarities, as well as different functional groups (acetaminophen, phenylephrine hydrochloride or phenylpropanolamine hydrochloride, chlorpheniramine maleate, 4-aminophenol, 4-chloracetanilide and 4-nitrophenol) at three pH levels (2.5, 4.6 and 7.0) and three proportions of buffer/acetonitrile (80:20, 50:50 and 20:80, v/v). The results obtained have permitted our group to develop unique applications with these columns, as these compounds are not only a test mixture, due to their chemical characteristics, but they are also usually contained in pharmaceutical formulations for the relief of common cold symptoms and have been selected as a real-life case study. Moreover, after observing the reversed-phase and normal-phase-like characteristics for certain analytes on the perfluorinated phase, a systematic study was developed in this column to understand the chromatographic behaviour of these compounds at three pH (2.5, 4.6 and 7.0) and seven different organic proportions from 20 to 80% acetonitrile. The predominant electrostatic interactions observed on the perfluorinated phase could explain its special behaviour and the high retention at higher percentages of organic solvent, especially for amine compounds, which makes this column very advantageous in working with LC/MS. Different applications with volatile buffers, such as TFA at pH 2.5 and ammonium acetate at pH 4.6 and 7.0, were also considered. Some results have been related to parameters frequently employed for column description.

Acetaminophen↗

PubMed2005

Capillary electrophoresis of glutathione to monitor oxidative stress and response to antioxidant treatments in an animal model.

Glutathione plays a central role in metabolism and antioxidant defence. Several factors can influence the analytical efficiency and rapidity of the quantitative determination of glutathione. Procedures in sample pre-treatment have been compared in order to minimize analytical errors. Capillary electrophoresis has been chosen as a more adequate technique for obtaining a rapid and simple method for glutathione and glutathione disulfide determination in the blood and liver of the rat. The methods, once optimised, have been validated and applied for monitoring the oxidative stress in an animal model, such as the rat made diabetic by streptozotocin injection, when the animals are treated with antioxidants and compared with the corresponding controls.

Animals↗

PubMed2005

New approaches with two cyano columns to the separation of acetaminophen, phenylephrine, chlorpheniramine and related compounds.

The development of new pharmaceutical forms with classical active compounds generates new analytical problems. That is the case of sugar-free sachets of cough-cold products containing acetaminophen, phenylephrine hydrochloride and chlorpheniramine maleate. Two cyanopropyl stationary phases have been employed to tackle the problem. The Discovery cyanopropyl (SUPELCO) column permitted the separation of the three actives, maleate and excipients (mainly saccharine and orange flavour) with a constant proportion of aqueous/ organic solvent (95:5, v/v) and a pH gradient from 7.5 to 2. The run lasted 14 min. This technique avoids many problems related to baseline shifts with classical organic solvent gradients and opens great possibilities to modify selectivity not generally used in reversed phase HPLC. On the other hand, the Agilent Zorbax SB-CN column with a different retention profile permitted us to separate not only the three actives and the excipients but also the three known related compounds: 4-aminophenol, 4-chloracetanilide and 4-nitrophenol in an isocratic method with a run time under 30 min. This method was validated following ICH guidelines and validation parameters showed that it could be employed as stability-indicating method for this pharmaceutical form.

Acetaminophen↗

PubMed2005

Major degradation product identified in several pharmaceutical formulations against the common cold.

Different pharmaceutical preparations against the common cold containing acetaminophen, phenylephrine hydrochloride, and chlorpheniramine have been studied. An unidentified degradation product has been discovered in these preparations after short- and long-term stability studies, with increasing concentration at increasing storage temperatures and times. LC/MS was employed to identify and obtain molecular weights of the degradation products using an electrospray ionization interface. To obtain detailed structural information on the major degradation product, its isolation by SPE followed by HPLC was required. Final isolation was accomplished by using a new pentafluorophenyl stationary phase. Once the major degradation product was isolated, MS/MS, 1H NMR, 13C NMR, COSY, HMBC, and HSQC techniques permitted the complete characterization of this new compound formed under the usual stability conditions at climatic chambers. Its origin was also established as a result of the interaction between two of the components in the formulation. It is important to remark that this compound has not been described in the literature up to now and that, moreover, it has been identified in several commercial preparations containing phenylephrine hydrochloride and chlorpheniramine maleate.

Chromatography, High Pressure Liquid↗

PubMed2005

LC methods for acyclovir and related impurities determination.

Acyclovir, guanine, and impurity A have been baseline separated with isocratic conditions at pH=3.0 and run time under 15 min by employing a SB-CN column from Agilent (150 mm x 4.6mm and 3.5 microm). Moreover, when run time was increased to 40 min six impurities (guanine, impurities A, F, G, Vir 3/4 and N(7)) plus acyclovir were separated in the same conditions. The mobile phase consisted of buffer A/acetonitrile 96:4 (v/v), being buffer A:25 mM H(3)PO(4) (Milli-Q H(2)O) brought to pH 3.0 with KOH. The same column provided separation for all the seven impurities described in pharmacopoeia, including impurity C, which coeluted with acyclovir in the previous conditions with a mobile phase prepared with 25 mM phosphoric acid (pH=1.8)/acetonitrile 96:4 (v/v). The method has been validated following ICH guidelines and it has demonstrated to be reliable for acyclovir and its impurities determination.

Acyclovir↗

PubMed2004

Evaluation of diabetes-related short-chain organic acids in rat plasma by capillary electrophoresis.

A capillary zone electrophoresis method was optimised to analyse low-molecular-mass organic acids for the purpose of monitoring diabetes in rat plasma. The method included acetoacetic, 2-hydroxybutyric, lactic and uric acids. A variation in the background electrolyte allowed us to measure pyruvic acid in the same sample. Conditions have been optimised for measuring a large number of plasma samples corresponding to control and diabetic rats. Samples were mixed with acetonitrile (1:1, v/v) to precipitate proteins, centrifuged, diluted and injected. Tropic acid was chosen as an adequate internal standard. Separation was developed with reversed voltage by using a column cartridge pre-treated with polyacrylamide. Two electrophoretic buffers were employed: 0.150 M H3PO4 made up pH 6.20 with NaOH and 0.3 mM CaCl2 for acetoacetic, hydroxybutyric, lactic and uric acids, and 200 mM phosphate-10 mM acetate pH 4.0 for pyruvic acid, both with direct detection at 200 nm. The method was validated for linearity, accuracy and precision and the limits of quantification were calculated. The method was successfully applied to analyse these organic acids in control and diabetic animals. Acetoacetic and hydroxybutyric acids were clearly increased in diabetic rats, meanwhile no statistically significant difference has been found with the other acids.

Animals↗

PubMed2004

High-performance liquid chromatographic analysis of dextromethorphan, guaifenesin and benzoate in a cough syrup for stability testing.

A method has been developed for the analysis of a cough syrup containing dextromethorphan, guaifenesin, benzoic acid, saccharin and other components. Forced degradation was also studied to demonstrate that the method could be employed during a stability study of the syrup. Final conditions were phosphate buffer (25 mM, pH 2.8) with triethylamine (TEA)-acetonitrile (75:25, v/v). In such conditions, all the actives, excipients and degradation products were baseline resolved in less than 14 min, and different wavelengths were used for the different analytes and related compounds.

Acetonitriles↗

PubMed2004

LC/MS for the degradation profiling of cough-cold products under forced conditions.

Heat, acid, base, UV radiation and oxidation stress methods were applied to study the stability of cough-cold products containing acetaminophen, phenylephrine or phenylpropanolamine hydrochloride and chlorpheniramine maleate. Liquid chromatography coupled with mass spectrometry was used to analyze the degraded samples and obtain molecular weights information. Different volatile buffers (ammonium bicarbonate and ammonium acetate) were assayed in LC/MS methods and retention times of the analytes were compared with those obtained in HPLC with UV detection employing a conventional sodium phosphate buffer to establish the possibility of results transference between the two systems.

Acetaminophen↗

PubMed2004

CE versus HPLC for the dissolution test in a pharmaceutical formulation containing acetaminophen, phenylephrine and chlorpheniramine.

A new polar reverse phase stationary phase has permitted our group to develop and validate an isocratic HPLC method for the simultaneous determination of acetaminophen, phenylephrine and chlorpheniramine in capsules as pharmaceutical formulation after their dissolution test. Final optimised chromatographic conditions employed a Supelco Discovery HS PEG column (polyethylene glycol), 5 microm, 15 cm x 0.46 cm. The mobile phase was 20 mM phosphate buffer at pH 7.0/acetonitrile 80:20 (v/v) at a flow rate of 1 ml/min. UV detection was performed at 210 nm for phenylephrine and chlorpheniramine and at 305 nm for acetaminophen. On the other hand, to evaluate the capability of CE to work in a routine analytical method fulfilling the pharmaceutical requirements and to study the behaviour of the technique with these compounds, we developed a CE method with the same objective. Normal and reverted polarity, the pH and concentration of the buffer, and the presence and concentration of surfactants were assayed. Forty millimolar phosphate buffer at pH 6.20 with 0.5 mM SDS at 30k V in an uncoated silica capillary provided a runtime of 4.5 min to separate the three analytes and the excipients. Moreover, parameters affecting precision in CE, such as the injection of buffer after the sample to refill the capillary were also tested. After development, the validation was performed in parallel for HPLC and CE with the same standards and samples to avoid differences due to the manipulation. The validation parameters of both techniques were adequate for the intended purpose.

Acetaminophen↗

PubMed2004

Direct liquid chromatography method for retinol, alpha- and gamma-tocopherols in rat plasma.

An HPLC method for Vitamins A and E in rat plasma has been developed. The main goals of the method are the small amount of sample, 50 microl, and the direct extraction of analytes in one step with acetone, which is a solvent compatible with the reverse-phase mobile phases. Recoveries, as compared with classical and more tedious methods, were near 100%. The method employs a Supelco Discovery C18 column and methanol/water (95:5, v/v) as mobile phase. After being developed, the method was validated following ICH guidelines, with UV, fluorescence and electrochemical detectors. It proved to be selective, lineal, accurate and precise. This method greatly simplifies sample treatment and that is a critical point when working with a large number of samples.

Animals↗

PubMed2003

LC determination of impurities in azithromycin tablets.

A LC method with UV detection for determining azithromycin impurities in tablets as pharmaceutical form has been developed. It is to be employed in routine and stability tests. A linear gradient elution was employed starting with 47% A and 53% B to reach 28% A and 72% B at 48 min. Mobile phase A was KH2PO4 10 mM (H2O) at pH 7.00. B was a mixture methanol:acetonitrile 1:1 (v/v). UV detection was performed at 210 nm. The chromatographic column was Phenomenex Synergi MAX-RP 4 microm 250 x 460 mm kept at 50 degrees C. Six impurities were separated and identified and it was possible to quantify five out of the six with reasonable accuracy and precision.

Acids↗

PubMed2003

Capillary electrophoresis determination of loratadine and related impurities.

While HPLC has traditionally been the method of choice for purity determination of pharmaceutical substances, capillary electrophoresis (CE) offers a different selectivity and hence it is a complementary technique to HPLC. Loratadine, an antihistamine, could include in its raw material seven impurities that ought to be separated, identified and quantified for drug development and quality control. As a complementary tool for undoubtful identification, a CE method has been developed. The separation was carried out with an uncoated fused-silica capillary (57 cm x 50 microm ID) and was operated at 20 kV potential. Temperature was maintained at 25 degrees C. The final separation buffer was prepared with 100 mM H(3)PO(4) made up to pH 2.5 with NaOH and with 10% acetonitrile added (v/v). Impurities can be detected at the 0.1% level of the active and validation parameters for linearity accuracy and precision are adequate for all the analytes and that permits to consider the method reliable and suitable for application to long-term stability and purity studies.

Drug Contamination↗

PubMed2003

Poly(ethyleneglycol) column for the determination of acetaminophen, phenylephrine and chlorpheniramine in pharmaceutical formulations.

New polar reversed-phase stationary phases in HPLC provide specific selectivities which can help to solve traditional chromatographic problems related to the development of chromatographic methods with widely different retention times for the sample components. One such case is the analysis of pharmaceutical formulations against the common cold. Acetaminophen, phenylephrine and chlorpheniramine, compounds with different polarities, are frequently associated in these drugs. An isocratic and rapid HPLC method for the simultaneous determination of the three compounds, acetaminophen, phenylephrine and chlorpheniramine, in capsules as pharmaceutical formulations, including the separation of impurities (4-aminophenol and 4-chloracetanilide) and excipients, has been developed and validated. The final chromatographic conditions employed a Supelco Discovery HS PEG column poly(ethyleneglycol) 15x0.46 cm, 5 microm. The mobile phase was 20 mM phosphate buffer, pH 7.0-acetonitrile (90:10, v/v) at a flow-rate of 1 ml/min. UV detection was performed at 215 nm for all the compounds except acetaminophen, which was measured at 310 nm. Validation parameters permit us to consider this method suitable.

Acetaminophen↗

PubMed2003

Uptake and distribution of zinc, cadmium, lead and copper in Brassica napus var. oleífera and Helianthus annus grown in contaminated soils.

Brassica napus var. oleifera and Helianthus annus were grown in artificially contaminated soils. Accumulation and translocation of the environmental pollutants zinc, cadmium, lead, and copper, was evaluated in different portions of the plants at two harvesting times. The distribution into the plants of these metal ions, as well as their capacity for contaminant phytoextraction and accumulation was assessed. For this purpose, an analytical method utilizing focused ultrasound employed for extraction and stripping voltammetry for measurement has been optimized and validated for the simultaneous measurement of Zn, Cd, Pb, and Cu in plant extracts.

Brassica napus↗

PubMed2002

Urinary analysis of nephrolithiasis markers.

Renal stone disease is an ancient and common affliction, common in industrialised nations. The causes and incidence of nephrolithiasis are presented. Afterwards, the promoters and inhibitors of renal stone formation analysis in urine are described including enzymatic methods, chromatography, capillary electrophoresis and other techniques. Aspects such as sample collection and storage are also included. The review article includes referenced tables that provide summaries of methodology for the analysis of nephrolithiasis related compounds.

Biomarkers↗