The development and validation of liquid chromatography method for the simultaneous determination of metformin and glipizide, gliclazide, glibenclamide or glimperide in plasma

This article describes the development of SPE and HPLC methods for the simultaneous determination of metformin and glipizide, gliclazide, glibenclamide or glimperide in plasma. Several extraction and HPLC methods have been described previously for the determination of each of these analytes in plasma separately. The simultaneous determination of these analytes is important for the routine monitoring of diabetic patients who take combination medications and for studying the pharmacokinetics of the combined dosage forms. In addition this developed method can serve as a standard method for the plasma determination of these analytes therefore saving time, effort and money. The recoveries of the developed methods were found to be between 76.3% and 101.9%. The limits of quantification were between 5 and 22.5 ng/ml. The intraday and interday precision (measured by coefficient of variation, CV%) was always less than 9%. The accuracy (measured by relative error %) was always less than 12%. Stability analysis showed that all analytes are stable for at least 3 months when stored at -70 degrees C.     

Determination of metformin in plasma by high-performance liquid chromatography after ultrafiltration

A rapid high-performance liquid chromatography (HPLC) method was developed for determination of metformin, an oral antidiabetic agent, in plasma. Sample preparation entailed a 30-min centrifugation of plasma through a micron filter with direct injection of the protein-free ultrafiltrate into an HPLC system consisting of a cation-exchange extraction column (7.5×4.6 mm), a column switching valve, and a cation-exchange analytical column (250×4.6 mm). The eluent was monitored at 232 nm. Metformin was well resolved at a retention time of about 5 min. There was less than 2% loss of metformin during ultrafiltration and good linearity was established from 0.10 to 40 mg/l of metformin hydrochloride. The lower limit of quantitation was about 0.05 mg/l, at which concentration the signal-to-noise was above 10. The intra- and inter-assay coefficients of variation at plasma concentrations of metformin hydrochloride between 0.25 and 25 mg/l were typically 0.8–1.4% and 3.5–6.4%, respectively. This method offers a rapid sample preparation time and achieves excellent sensitivity without resorting to extraction and evaporation techniques.     

Simultaneous quantification of free nucleotides in complex biological samples using ion pair reversed phase liquid chromatography isotope dilution tandem mass spectrometry

A new sensitive and accurate analytical method has been developed for quantification of intracellular nucleotides in complex biological samples from cultured cells of different microorganisms such as Saccharomyces cerevisiae, Escherichia coli, and Penicillium chrysogenum. This method is based on ion pair reversed phase liquid chromatography electrospray ionization isotope dilution tandem mass spectrometry (IP-LC-ESI-ID-MS/MS. A good separation and low detection limits were observed for these compounds using dibutylamine as volatile ion pair reagent in the mobile phase of the LC. Uniformly ¹³C-labeled isotopes of nucleotides were used as internal standards for both extraction and quantification of intracellular nucleotides. The method was validated by determining the linearity, sensitivity, and repeatability.     

Dried blood spot liquid chromatography assay for therapeutic drug monitoring of metformin

The use of blood spot collection cards is a simple way to obtain specimens for analysis of drugs for the purpose of therapeutic drug monitoring, assessing adherence to medications and preventing toxicity in routine clinical setting. We describe the development and validation of a microanalytical technique for the determination of metformin from dried blood spots. The method is based on reversed phase high-performance liquid chromatography with ultraviolet detection. Drug recovery in the developed method was found to be more than 84%. The limits of detection and quantification were calculated to be to be 90 and 150 ng/ml, respectively. The intraday and interday precision (measured by CV%) was always less than 9%. The accuracy (measured by relative error, %) was always less than 12%. Stability analysis showed that metformin is stable for at least 2 months when stored at -70 degrees C. The small volume of blood required (10 microL), combined with the simplicity of the analytical technique makes this a useful procedure for monitoring metformin concentrations in routine clinical settings. The method is currently being applied to the analysis of blood spots taken from diabetic patients to assess adherence to medications and relationship between metformin level and metabolic control of diabetes.     

Determination of metformin in human plasma by high-performance liquid chromatography

A simple, selective and sensitive high-performance liquid chromatographic method with spectrophotometric detection was developed for the determination of antihyperglycemic agent metformin in human plasma using a novel sample extraction procedure. Liquid-liquid extraction of metformin and ranitidine (as internal standard) from plasma samples was performed with 1-butanol/n-hexane (50:50, v/v) in alkaline condition followed by back-extraction into diluted acetic acid. Chromatography was carried out using a silica column (250 mmx4.6 mm, 5 microm) under isocratic elution with acetonitrile-40 mM aqueous sodium dihydrogen phosphate (25:75, v/v), pH 6. The limit of quantification (LOQ) was 15.6 ng/ml and the calibration curves were linear up to 2000 ng/ml. The mean absolute recoveries for metformin and internal standard using the present extraction procedure were 98 and 95%, respectively. The intra- and inter-day coefficient of variation and percent error values of the assay method were all less than 8.3%.     

Simple liquid chromatography method for the rapid simultaneous determination of prednisolone and cortisol in plasma and urine using hydrophilic lipophilic balanced solid phase extraction cartridges

This article describes the development and validation of a simple solid phase extraction (SPE) and HPLC method for the extraction and the specific determination of prednisolone and hydrocortisone (cortisol) in both plasma and urine using one washing step with Oasis hydrophilic lipophilic balanced (HLB) cartridges (1 ml/30 mg, 30 microm). Recoveries of prednisolone and cortisol from plasma and urine exceeded 82%. The limit of quantification (LOQ) in plasma and urine was 9.9 and 6.7 ng/ml for cortisol, respectively, and 11.6 and 8.0 ng/ml for prednisolone, respectively. The intraday and interday precision (measured by CV%) for both prednisolone and cortisol in both plasma and urine was always less than 7%. The accuracy (measured by relative error %) for both prednisolone and cortisol in both plasma and urine was always less than 8%. The advantages of the developed method are the use of a one step washing SPE utilising HLB cartridges which do not suffer the drying out problems of conventional SPE cartridges and the time saving when compared with solvent extraction (SE), in addition to the simultaneous determination of prednisolone and cortisol in both plasma and urine.     

Simultaneous determination of metformin and rosiglitazone in human plasma by liquid chromatography/tandem mass spectrometry with electrospray ionization: application to a pharmacokinetic study

A selective and sensitive high performance liquid chromatography-electrospray ionization-tandem mass spectrometry (ESI-MS/MS) method for simultaneous determination of metformin and rosiglitazone in human plasma using phenformin as internal standard (IS) has been first developed and validated. Plasma samples were precipitated by acetonitrile and the analytes were separated on a prepacked Phenomenex Luna 5u CN 100A (150 mm x 2.0 mm I.D.) column using a mobile phase comprised of methanol:30 mM ammonium acetate pH 5.0 (80:20, v/v) delivered at 0.2 ml/min. Detection was performed on a Finnigan TSQ triple-quadrupole tandem mass spectrometer in positive ion selected reaction monitoring (SRM) mode using electrospray ionization. The ion transitions monitored were m/z 130.27-->71.11 for metformin, m/z 358.14-->135.07 for rosiglitazone and m/z 206.20-->105.19 for the IS. The standard curves were linear (r(2)>0.99) over the concentration range of 5-3000 ng/ml for metformin and 1.5-500 ng/ml for rosiglitazone with acceptable accuracy and precision, respectively. The within- and between-batch precisions were less than 15% of the relative standard deviation. The limit of detection (LOD) of both metformin and rosiglitazone was 1 ng/ml. The method described is precise and sensitive and has been successfully applied to the study of pharmacokinetics of compound metformin and rosiglitazone capsules in 12 healthy Chinese volunteers.     

Enrichment and analysis of RNA centered on ion pair reverse phase methodology

Here we describe a procedure for the rapid enrichment of RNA from cell extracts and the subsequent fractionation and analysis of the "small RNA" population by ion pair reverse phase chromatography. Solid phase extraction procedures have been developed utilizing nonporous alkylated poly(styrene-divinylbenzene) particles in conjunction with ion pair reagents to enrich total RNA. This approach facilitates the selective enrichment and separation of the relatively lower abundance small RNAs, from the more abundant higher molecular weight rRNA species. We also describe the application of monolithic capillaries in conjunction with ion pair reverse phase chromatography to bring increased sensitivity in the analysis of very low abundance RNAs. These approaches will simplify the biochemical analysis of this class of molecules, which are emerging as important regulators of global gene expression in higher organisms.     

Liquid chromatographic determination of oxcarbazepine and its metabolites in plasma of epileptic patients after solid-phase extraction

A method based on high-performance liquid chromatography with UV detection in combination with solid-phase extraction for sample pretreatment has been developed for the simultaneous analysis of the antiepileptic drug oxcarbazepine and its main metabolites in human plasma. The extraction of the analytes from plasma samples was carried out by means of a selective solid-phase extraction procedure using hydrophilic-lipophilic balance cartridges. The separation was obtained on a reversed-phase column (C(18), 150x4.6 mm I.D., 5 micrometer) using a phosphate buffer-acetonitrile-methanol-triethylamine mixture (final apparent pH* 3.5) as the mobile phase. Under these chromatographic conditions, oxcarbazepine and its metabolites 10,11-dihydro-10-hydroxycarbamazepine, 10,11-dihydro-10,11-dihydroxycarbamazepine and the internal standard are baseline separated in less than 9 min. The extraction yield values were >94% for all analytes and the precision, expressed by the RSD%, was in the low percentage range. For the entire method, including sample pre-treatment and HPLC determination, the linearity of the calibration lines, expressed by the linear correlation coefficient, was better than 0.995; the limit of quantitation was 15 ng ml(-1). The method was applied to plasma samples from patients undergoing chronic treatment with oxcarbazepine, both in monotherapy and in polytherapy. Based on the analytical parameters precision, accuracy, limit of quantitation and analysis time the method is suitable for routine application in therapeutic drug monitoring.     

Method development and validation of a high-performance liquid chromatographic method for tramadol in human plasma using liquid-liquid extraction

An HPLC system using a simple liquid-liquid extraction and HPLC with UV detection has been validated to determine tramadol concentration in human plasma. The method developed was selective and linear for concentrations ranging from 10 to 2000 ng/ml with average recovery of 98.63%. The limit of quantitation (LOQ) was 10 ng/ml and the percentage recovery of the internal standard phenacetin was 76.51%. The intra-day accuracy ranged from 87.55 to 105.99% and the inter-day accuracy, 93.44 to 98.43% for tramadol. Good precision (5.32 and 6.67% for intra- and inter-day, respectively) was obtained at LOQ. The method has been applied to determine tramadol concentrations in human plasma samples for a pharmacokinetic study.     

Determination of pentacaine, trans-2-(1-pyrrolidinyl)cyclohexyl-3-pentyloxycarbanilate hydrochloride, in biological samples by gas chromatography/mass spectrometry

A quantitative and selective method has been developed for the determination of a novel local anaesthetic compound pentacaine, trans-2-(1-pyrrolidinyl)cyclohexyl-3-pentyloxycarbanilate hydrochloride, in biological samples. After ion pair extraction from 1 M HCl into 1,2-dichloroethane, pentacaine and a structurally related internal standard were derivatized to prevent thermal decomposition in the gas chromatograph. An on-column methylation technique with trimethylanilinium hydroxide was used. Determination was performed by gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring. Interferences by endogenous lipophilic constituents were avoided by including an n-hexane wash before the ion pair extraction. This wash step did not reduce the drug recoveries. The method gave linear results over a concentration range of 5-100 ng ml-1 with a coefficient of variation less than 10% at 5 ng pentacaine ml-1. Specimens of plasma, whole blood, urine as well as in vitro preparations such as hepatic microsomes were successfully analysed.     

High-performance liquid chromatography coupled with negative ion tandem mass spectrometry for determination of pravastatin in human plasma

A new method, using high-performance liquid chromatography/ion electrospray (negative ion) mass spectrometry, has been developed for the determination of a hydrophilic liver-specific inhibitor of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase, pravastatin in human plasma. In this method, plasma samples were prepared by a solid-phase extraction on C(18) Bond Elut cartridge. Chromatography was carried out with a Zorbax C(8) column. Simple isocratic chromatography conditions were used. The method has been validated in a linear range of 0.25-300 ng/ml with a coefficient of variation of 0.6-3.4%. The overall recovery was 90.5% for pravastatin and 90.8% for the internal standard beta-hydroxy-lovastatin. The method is simple and reliable with a total run time of less than 2 min.     

Determination of grepafloxacin in plasma and urine by a simple and rapid high-performance liquid chromatographic method

A rapid, specific, sensitive and economical method has been developed and validated for the determination of grepafloxacin in human plasma and urine. The assay consisted of reversed-phase HPLC with UV detection. Plasma proteins were removed by a fast and efficient procedure that has eliminated the need for costly extraction and evaporation. For the urine samples, the only required sample preparation was dilution. Separation was achieved on a reversed-phase TSK gel column with an isocratic mobile system. The method had a quantification limit of 0.05 μg/ml in plasma and 0.5 μg/ml in urine. The coefficients of variation (C.V.) were less than 4% for within- and between-day analyses. The method was successfully applied to a pharmacokinetic study, and was proved to be simple, fast and reproducible.     

Determination of cefaclor in human plasma by a sensitive and specific liquid chromatographic-tandem mass spectrometric method

A sensitive and specific liquid chromatographic-tandem mass spectrometric method is described for the determination of cefaclor in human plasma. The plasma samples were treated by two sample preparation procedures, i.e. protein precipitation (PPT) and solid-phase extraction (SPE). The pretreated samples were analyzed on a C(18) HPLC column interfaced with a triple quadrupole tandem mass spectrometer. Positive electrospray ionization (ESI) was employed as the ionization source. The analyte and internal standard ampicillin (for PPT) or cefetamet (for SPE) were detected by use of selected reaction monitoring (SRM) mode. The lower limit of quantitation obtained as a result of the PPT procedure was 100 ng/ml. The intra- and inter-run precision, calculated from quality control (QC) samples was less than 12% for cefaclor. The accuracy as determined from QC samples was within +/-3% for the analyte. The SPE procedure could provide the lower limit of quantitation of 2 ng/ml. The precision and accuracy were measured to be below 7.1% and between -3.6% and 1.1%, respectively, for all QC samples. The method was applied for the evaluation of the pharmacokinetic profiles of cefaclor sustained-release formulation.     

Development and validation of a liquid chromatography-tandem mass spectrometry method for the determination of xanthinol in human plasma and its application in a bioequivalence study of xanthinol nicotinate tablets

A sensitive, rapid liquid chromatographic-electrospray ionization mass spectrometric method for the determination of xanthinol in human plasma was developed and validated. Xanthinol nicotinate in plasma (0.5mL) was pretreated with 20% trichloroacetic acid for protein precipitation. The samples were separated using a Lichrospher silica (5mum, 250mmx4.6mm i.d.). A mobile phase of methanol-water containing 0.1% formic acid (50: 50, v/v) was used isocratically eluting at a flow rate of 1mL/min. Xanthinol and its internal standard (IS), acyclovir, were measured by electrospray ion source in positive selected reaction monitoring mode. The method demonstrated that good linearity ranged from 10.27 to 1642.8ng/mL with r=0.9956. The limit of quantification for xanthinol in plasma was 10.27ng/mL with good accuracy and precision. The mean plasma extraction recovery of xanthinol was in the range of 90.9-100.2%. The intra- and inter-batch variability values were less than 4.8% and 7.9% (relative standard deviation, R.S.D.), respectively. The established method has been successfully applied to a bioequivalence study of two xanthinol nicotinate tablets for 20 healthy volunteers.     

Determination of 5-fluorouracil in environmental samples by solid-phase extraction and high-performance liquid chromatography with ultraviolet detection

5-Fluorouracil (5-FU) is one of the most widely used antineoplastic drugs. It can be therefore considered to be a model compound for the identification of exposure routes during preparation and administration of cytostatic agents, especially for nucleoside analogue drugs. In this study, an HPLC–UV method was validated for determination of 5-FU in wipe samples by direct analysis of the aqueous solutions and in air samples by using solid-phase extraction (SPE). When samples were pre-treated on styrene–divinylbenzene resin SPE columns, a 20-fold preconcentration of the analyte was achieved. As regards air samples, correlation coefficients were always higher than 0.998 and the limit of detection was assessed at 15 ng on filter. In order to verify the reliability of these procedures, 5-chlorouracil was used as internal standard. The procedure presented here has been applied to the environmental monitoring of occupational exposed subjects. The amount of 5-FU ranged from 0.043 to 0.23 μg/m³ in air samples and from 0.2 to 470.1 μg/dm² in wipe samples. 5-FU was also detected on the internal side of the gloves (0.07 to 3.77 μg/pair of gloves).     

Rapid and sensitive liquid chromatography-tandem mass spectrometric method for the quantitation of metformin in human plasma

A rapid and sensitive liquid chromatography-tandem mass spectrometric (LC-MS-MS) method for the determination of metformin in human plasma using phenformin as internal standard has been developed and validated. Sample preparation of plasma involved acidification with acetic acid, deproteination with acetonitrile and washing with dichloromethane. Samples were then analyzed by HPLC on a short Nucleosil C18 column (5 microm, 50 mm x 4.6 mm i.d.) using a mobile phase consisting of acetonitrile:methanol:10mM ammonium acetate pH 7.0 (20:20:60, v/v/v) delivered at 0.65 ml/min. Detection was performed using an Applied Biosystems Sciex API 4000 mass spectrometer set at unit resolution in the multiple reaction monitoring (MRM) mode. Atmospheric pressure chemical ionization (APCI) was used for ion production. The assay was linear over the range 1-2000 ng/ml with intra- and inter-day precision of <8.6% and accuracy in the range 91-110%. The limit of detection was 250 pg/ml in plasma. The method was successfully applied to a clinical pharmacokinetic study of an extended-release tablet of metformin hydrochloride (500 mg) administered as a single oral dose.     

Development and validation of a HPLC method for the quantitation of ochratoxins in plasma and raw milk

A HPLC method with improved sensitivity for the determination of ochratoxins (OT) A, B and alpha in plasma and milk was developed. Plasma analysis involved a simple liquid-liquid extraction with chloroform; while for milk, an additional immunoaffinity clean-up step was necessary. The method showed a good linearity (r(2)>0.999). The limit of quantification (LOQ) of OTA was 5 and 200 ng/l for milk and plasma, respectively. Average recovery was 89% in both matrices, except for OTalpha in milk that was only 18% due to poor immunoaffinity binding. OT remained stable in -20 degrees C stored samples; OTA concentration in plasma and milk did not change after 8 and 18 months of storage, respectively. The developed method has been applied to contaminated plasma and milk samples obtained from dairy ewes fed with ochratoxin-contaminated feed.     

Direct injection of human serum and pharmaceutical formulations for glucosamine determination by CE-C(4)D method

A simple CE-C(4)D method has been developed for the determination of glucosamine by direct injection of human serum and pharmaceutical samples. Glucosamine was electrokinetically injected and analysed in its protonated form using 20mM MES/His (pH 6) as background electrolyte in order to separate it from the matrix and to provide a better response to the C(4)D detector. Separation of glucosamine in human serum and pharmaceutical samples was performed in 3 min without the need for protein precipitation or matrix removal. Good precision in terms of %RSD for the migration time and peak area were less than 1.91% (n = 10). The conductivity signal was linear with glucosamine concentration in the range 0.10-2.50mg/mL, with a detection limit of 0.03 mg/mL. Recoveries of glucosamine in serum and pharmaceutical samples were 86.5-104.78%. The method was successfully applied for the determination of the glucosamine content in pharmaceutical formulations and validated with high performance liquid chromatography (HPLC). Good agreements were observed between the developed method, label values and the HPLC method. Glucosamine could be detected in spiked serum sample by direct injection. This was not possible by HPLC due to co-eluting interferences.     

Quantitation of salbutamol in human urine by liquid chromatography-electrospray ionization mass spectrometry

A sensitive and specific liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) is described for quantitation of salbutamol in human urine using nadolol as the internal standard (I.S.). Urine samples were hydrolyzed with beta-glucuronidase followed by a solid-phase extraction procedure using Bond Elut-Certify cartridges. The HPLC column was an Agilent Zorbax SB-C(18) column. A mixture of 0.01 M ammonium formate buffer (pH 3.5)-acetonitrile (85:15, v/v) was used as the mobile phase. Analytes were quantitated using positive electrospray ionization in a quadrupole spectrometer. Selected ion monitoring (SIM) mode was used to monitor m/z 166 for salbutamol and m/z 310 for I.S. Good linearity was obtained in the range of 10.0-2000.0 ng/ml. The limit of quantification was 10.0 ng/ml. The intra- and inter-run precision, calculated from quality control (QC) samples was less than 7.3%. The accuracy as determined from QC samples was within +/-2.6%. The method was applied for determining excretion curves of salbutamol.