Intravenous administration of 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxy chroman (gamma-CEHC) to rats and determination of its plasma concentration and urinary sodium excretion

A natriuretic hormone, 2,7,8-trimethyl-2-(beta-carboxyethyl)-6-hydroxy chroman (gamma-CEHC) was administered intravenously to male Sprague-Dawley rats and the plasma concentration of gamma-CEHC along with urinary sodium (Na+) excretion was investigated. The plasma gamma-CEHC concentrations were fluorimetrically determined by a column-switching HPLC method consisting of both phenyl and octadecyl silica columns, following a pre-column fluorescence derivatization with a fluorescence reagent, 4-N,N-dimethylaminosulfonyl-7-piperazino-2,1,3-benzoxadiazole (DBD-PZ). In rats fed with a high-NaCl (8.0%) diet, plasma gamma-CEHC concentrations rapidly decreased by 20% in 15-45 min after the administration of gamma-CEHC, while Na+ excretion gradually increased with time. Considering these results, the Na+ excretion effect appeared not to be associated with plasma gamma-CEHC concentration. In addition, attempts were made to examine a main urinary metabolite of gamma-CEHC, a large amount of 6-O-sulfated gamma-CEHC found to be present in the urine using an HPLC-tandem mass spectrometry. Thus, it is plausible that gamma-CEHC was easily metabolized to 6-O-sulfated metabolite and excreted into urine in rats.     

A rapid HPLC method for the determination of carboxylic acids in human urine using a monolithic column

A rapid HPLC method for the determination of carboxylic acids in urine samples using a Chromolith Performance RP/18e 100/4.6 with Chromolith Guard Cartridge RP/18e 10/4.6 (Merck KgaA, Darmstadt, Germany) was developed. The method facilitates the simultaneous determination of aromatic hydrocarbon metabolites mandelic acid (MA) and phenylglyoxylic acid (PGA) from styrene and ethylbenzene, hippuric acid (HA) from toluene and 2-, 3-, 4-methylhippuric acids (MHA) from xylene. 3-Hydroxybenzoic acid (3-HBA) was used as internal standard. A chromatographic run is completed within less than 5 min for styrene, ethylbenzene and toluene metabolites, and within 10 min for xylene metabolites. The detection limits are 9 mg L^–1 urine for MA, 1.25 mg L^–1 urine for PGA, 4.9 mg L^–1 urine for HA, 22 mg L^–1 urine for 2-MHA, and 18.5 mg L^–1 urine for 3-MHA.No significant differences of the MA, PGA and HA concentrations in human urine samples obtained by HPLC chromatography on LiChrosorb RP 18 and on Chromolith RP/18e columns were found. The results were evaluated by using ANOVA.Abbreviations MA mandelic acid - PGA phenylglyoxylic acid - HA hippuric acid - MHA methylhippuric acid - 3-HBA 3-hydroxybenzoic acid - ANOVA analyses of variance - GC gas chromatography - HPLC high-performance liquid chromatography     

Development and validation of a HPLC method for determination of levonorgestrel and quinestrol in rat plasma

Levonorgestrel and quinestrol, commonly known as EP‐1, has long been used in the control of wild rodents. Up to the present time, however, no method for simultaneous quantification of levonorgestrel and quinestrol in rat plasma has been reported. In the present study, a sensitive reverse‐phase high‐performance liquid chromatography with ultraviolet detection (RP‐HPLC‐UV) method for quantification of levonorgestrel and quinestrol in rat plasma has been developed. It uses a Kromasil ODS C₁₈ column and acetonitrile‐0.1% formic acid (85 : 15, v/v) mobile phase at ambient temperature. The plasma sample was prepared by hexane–isoamyl alcohol extraction (90 : 10, v/v). The flow rate and detection wavelength were 1.0 mL/min and 230 nm. The correlation coefficients were greater than 0.9995 within 0.08–50 μg/mL for levonorgestrel and 0.12–50 μg/mL for quinestrol, and the limits of detection were 0.02 and 0.05 μg/mL for levonorgestrel and quinestrol, respectively. Average recovery ranged from 92.5 to 96.3% and inter‐day RSDs were less than 7.56%. This method can be applied to the further pharmacokinetic study of levonorgestrel and quinestrol in rat plasma. Copyright © 2009 John Wiley & Sons, Ltd.     

Development and validation of an RP-HPLC-UV method for the determination of BOL-303225-A, a new coumarin-based anti-inflammatory drug, in rat plasma

A simple and rapid high-performance liquid chromatographic method was developed and validated for the analysis in rat plasma of BOL-303225-A, a new coumarin-based anti-inflammatory drug. Liquid-liquid extraction was used for sample preparation. Chromatographic separation was achieved on a C(18) column using acetonitrile and water containing 1% triethylamine pH 3.5, adjusted with orthophosphoric acid (35.5:64.5 v/v) as mobile phase. The UV detector was set at 324 nm. The method proved to be linear (r(2) > 0.99) and precise (RSD < 7%) over the concentration range 29-940 ng/mL, and was suitable for the support of pharmacokinetic studies in rats.     

Fluorescence determination of N-acetylaspartic acid in the rat cerebrum homogenate using high-performance liquid chromatography with pre-column fluorescence derivatization

N-acetyl-L-aspartic acid (NAA) is an endogenous compound, and its brain concentration is suggested to be altered in neurological disorders. In the present study, a fluorescence determination method for NAA was developed by employing reversed-phase high-performance liquid chromatography (HPLC) with pre-column fluorescence derivatization using 4-N,N-dimethylaminosulfonyl-7-N-(2-aminoethyl)amino-2,1,3-benzoxadiazole (DBD-ED). Using methylsuccinic acid as the internal standard, a linear calibration curve for NAA was constructed in the range 125-1000 microM (n=3). The detection limit on the column was approximately 5.0 fmol (signal-to-noise ratio 3). The proposed HPLC method was applied to determine NAA in the rat cerebrum homogenate. Cerebrum NAA was successfully determined using 10 microL of the homogenate, and the validation data for the proposed HPLC method demonstrated satisfactory results. Intra- and inter-day precision and accuracy were within 1.1-7.0 and -8.1-6.3%, respectively. The concentration of NAA in the male rat cerebrum (13 weeks old) was 84+/-4.6 micromol/mg protein (n=3).     

Analysis of carboxylic acid metabolites from the tricarboxylic acid cycle in Bacillus subtilis cell extract by capillary electrophoresis using an indirect photometric detection method

With a growing interest in metabolome analysis, there is a need for developing robust methods for analysis of intracellular metabolites profiles in real samples like e.g., bacteria cell. Due to their weak absorbance properties, tri- and dicarboxylic acids from TCA cycle (citric, isocitric, 2-oxoglutaric, succinic, fumaric, malic) as well as carboxylic acid metabolites from glycolysis pathway, urea cycle and metabolism of amino compounds (formic, pyruvic, lactic, acetic, glutamic) were analyzed by capillary electrophoresis (CE) with indirect UV detection. Using 4 mM 2,6-pyridinedicarboxylic acid as a highly UV absorbing carrier electrolyte, 0.2 mM cetyltrimethylammonium bromide, 10% ethylene glycol and 10% acetonitrile, pH 3.5, carboxylic acids metabolites were analyzed in Bacillus subtilis cell extract from two different cultures: glucose and malate. CE with an electrokinetic injection mode achieved limits of detection in the range of 13-54 ppb (1.12-10(-7) - 5.96-10(-7) M). The reproducibility and linearity of method was investigated with RSD for migration time less than 1.3% and acceptable correlation coefficients. The optimized CE method was used to compare metabolome content of cell extract derived from two different culture media containing either glucose or malate as a carbon source. The changes in carboxylic acid metabolites profile were observed depending from used culture medium. Carboxylic acid concentrations ranged: in cell extract from malate culture from 59 to 0.5 microM for lactate and citrate, respectively, and in cell extract from glucose culture from 133 to 0.5 microM for glutamate and citrate, respectively. Appropriate concentrations of carboxylic acid in the single bacterium cell were estimated at mM and sub-mM levels.     

Development of a one-pot method for the homologation of aldehydes to carboxylic acids

A highly efficient method is described for the one-carbon homologation of aldehydes to carboxylic acid derivatives employing the reaction of a 1,1-bis-dimethylphosphonate derivative with the aldehyde and controlled acid hydrolysis of the derived α-phosphonoenamine intermediate.     

Development of LC‐MS/MS method for the determination of dapiprazole on dried blood spots and urine: application to pharmacokinetics

A rapid and highly sensitive liquid chromatography–tandem mass spectrometric (LC‐MS/MS) method for determination of dapiprazole on rat dried blood spots and urine was developed and validated. The chromatographic separation was achieved on a reverse‐phase C₁₈ column (250 × 4.6 mm i.d., 5 µm), using 20 mm ammonium acetate (pH adjusted to 4.0 with acetic acid) and acetonitrile (80:20, v/v) as a mobile phase at 25 °C. LC‐MS detection was performed with selective ion monitoring using target ions at m/z 326 and m/z 306 for dapiprazole and mepiprazole used as internal standard, respectively. The calibration curve showed a good linearity in the concentration range of 1–3000 ng/mL. The effect of hematocrit on extraction of dapiprazole from DBS was evaluated. The mean recoveries of dapiprazole from DBS and urine were 93.88 and 90.29% respectively. The intra‐ and inter‐day precisions were <4.19% in DBS as well as urine. The limits of detection and quantification were 0.30 and 1.10 ng/mL in DBS and 0.45 and 1.50 ng/mL in urine samples, respectively. The method was validated as per US Food and Drug Administration guidelines and successfully applied to a pharmacokinetic study of dapiprazole in rats. Copyright © 2013 John Wiley & Sons, Ltd.     

A simple and sensitive HPLC‐UV determination of 7‐O‐succinyl macrolactin A in rat plasma and urine and its application to a pharmacokinetic study

A simple, sensitive and reproducible isocratic reversed‐phase (C₁₈) high‐performance liquid chromatography (HPLC) method was developed to determine 7‐O‐succinyl macrolactin A (SMA) in rat plasma and urine samples using UV detector set at 230 nm. Lamotrigine was used as internal standards (IS) to ensure the precision and accuracy of the method. The retention times of SMA and IS for the plasma sample were 9.2 and 4.4 min, respectively, and those for the urine samples were 7.9 and 4.3 min, respectively. The intra‐ and inter‐day variations of the analytical responses, expressed in terms of relative standard deviation, were less than 14.9%. The accuracy, in terms of average analytical recovery, ranged from 90.4 to 119%. The lower limits of quantification of SMA in rat plasma and urine samples were 0.02 and 0.1 µg/mL, respectively. This method is applicable for the pharmacokinetic studies of SMA in rats. Copyright © 2012 John Wiley & Sons, Ltd.     

Development and validation of a reversed-phase HPLC method for determination of nitrendipine in rat plasma: application to pharmacokinetic studies

A simple and sensitive method for the determination of nitrendipine in rat plasma was developed using high-performance liquid chromatography (HPLC). The procedure involves extraction of nitrendipine in dichloromethane/sodium hydroxide, followed by reversed phase HPLC using a Waters, Spherisorb ODS2 (250 x 4.6 mm, 5 microm) column and UV detection at 238 nm. The retention times of nitrendipine and internal standard (felodipine) were 5.0 min and 7.5 min, respectively. The calibration curves were linear over the range of 5 ng/mL (lower limit of quantification, LOQ) to 200 ng/mL for nitrendipine. The intra- and inter-day coefficients of variation for all criteria of validation were less than 15% over the linearity range. The sensitivity and precision of the method were within the accepted limits (< 15%) throughout the validation period. The present method was also successfully applied for the study of plasma pharmacokinetics of nitrendipine loaded solid lipid nanoparticles (SLN) in rats.     

Development and validation of a HPLC method for quantification of rivastigmine in rat urine and identification of a novel metabolite in urine by LC‐MS/MS

A sensitive, specific and accurate HPLC method for the quantification of rivastigmine (RSM) in rat urine was developed and validated. The method involves the simple liquid–liquid extraction of RSM and pyridostigmine as an internal standard (IS) from rat urine with tertiary methyl butyl ether. The chromatographic separation of RSM and IS was achieved with 20 mm ammonium acetate buffer (pH 6.5) and acetonitrile (65:35, v/v) delivered at flow‐rate of 1 mL/min on a Kromasil KR‐100. The method was in linear range from 50 to 5000 ng/mL. The validation was done as per FDA guidelines and the results met the acceptance criteria. The method was successfully applied for the quantification of RSM in rat urine. Besides method validation, we have identified two metabolites of RSM in urine. Both the metabolites were characterized by HPLC‐PDA and LC‐MS/MS and it was found that one metabolite is novel. Copyright © 2010 John Wiley & Sons, Ltd.     

Determination of memantine in rat plasma by HPLC-fluorescence method and its application to study of the pharmacokinetic interaction between memantine and methazolamide

A sensitive high-performance liquid chromatographic method with fluorescence detection was developed to determine memantine (MT) in rat plasma. The method consists of pre-column labeling of MT with 4-(4,5-diphenyl-1H-imidazol-2-yl)benzoyl chloride (DIB-Cl) and a clean-up step with solid-phase extraction. A good separation of DIB-MT was achieved within 12 min on an octadecylsilica (ODS) column (150 × 4.6 mm i.d.; 5 μm) with a mobile phase of acetonitrile-water (70:30, v/v). The calibration curve prepared with fluoxetine as an internal standard showed good linearity in the range of 10-400 ng/mL (r = .999). The limits of detection and quantitation at signal-to-noise ratios of 3 and 10 were 2.0 and 6.6 ng/mL, respectively. The method was shown to be reliable with precisions of <5% for intra-day and <9% for inter-day as relative standard deviation. The fluorescence property and reaction yield of authentic DIB-MT were also examined. The proposed method was successfully applied to study the pharmacokinetic interaction between MT and methazolamide.     

Development and validation of a reliable high-performance liquid chromatographic method for determination of nodakenin in rat plasma and its application to pharmacokinetic study

A simple and reliable high-performance liquid chromatographic (HPLC) method has been developed for the determination of nodakenin in rat plasma. The concentration of nodakenin was determined in plasma samples after deproteinization with methanol using hesperidin as internal standard. HPLC analysis was performed on a Diamonsil C(18) analytical column using acetonitrile-water (25:75, v/v) as the mobile phase and a UV detection at 330 nm. This method was validated in terms of recovery, linearity, accuracy and precision (intra- and inter-day variation). The extraction recoveries were 91.3 ± 10, 87.8 ± 4.8 and 92.6 ± 5.1 at concentrations of 0.500, 5.00 and 40.0 μg/mL, respectively. The standard curve for nodakenin was linear (r(2) ≥ 0.99) over the concentration range 0.250-50.0 μg/mL with a lower limit of quantification of 0.250 μg/mL. The intra- and inter-day precision (relative standard deviation, RSD) values were not higher than 12% and the accuracy (relative error, RE) was within ± 5.8% at three quality control levels. The validated method was successfully applied for the evaluation of the pharmacokinetics of nodakenin in rats after oral administration of Rhizoma et Radix Notopterygii decoction and nodakenin solution.     

Development of a sensitive liquid chromatography/tandem mass spectrometry method for the determination of fenofibric acid in rat plasma

A rapid and sensitive LC‐MS/MS method for the quantification of fenofibric acid in rat plasma was developed and validated. Plasma samples were prepared by liquid–liquid extraction with a mixture of N‐hexane–dichloromethane–isopropanol (100:50:5, v/v/v). Isocratic chromatographic separation was performed on a reversed‐phase Discovery C₁₈ column (2.1 × 50 mm, 5 µm). The mobile phase was methanol–water–formic (75:25:0.25, v/v/v). Detection of fenofibric acid and the internal standard (IS) diclofenac acid was achieved by ESI MS/MS in the negative ion mode using m/z 317 → m/z 213 and m/z 294 → m/z 250 transitions, respectively. The method was linear from 0.005 to 1.250 µg/mL when 100 μL plasma was analyzed. The lower limit of quantification was 0.005 µg/mL. The intra‐ and inter‐day precision values were below 8.2%, and accuracy ranged from ?0.9 to 2.1% in all quality control samples. The recovery was 90.3–94.7% and 83.3% for fenofibric acid and IS, respectively. Total run time for each sample analysis was 2.5 min. The validated method was successfully applied to a pharmacokinetic study in six rats after oral administration of fenofibrate, the ester prodrug of fenofibric acid (equivalent to fenofibric acid 5 mg/kg). The method permits laboratory scientists with access to the appropriate instrumentation to perform rapid fenofibric acid determination. Copyright © 2011 John Wiley & Sons, Ltd.     

High-performance liquid chromatographic method for the determination of mangiferin in rat plasma and urine

A reversed-phase high-performance liquid chromatography assay for mangiferin in rat plasma and urine was developed. Rutin was employed as an internal standard. The mobile phase consisted of acetonitrile-water (16:84, v/v) containing 3% acetic acid at a flow rate of 1 mL/min. Detection was at 257 and 365 nm for mangiferin in plasma and urine, respectively. The limit of quantitation (LOQ) of mangiferin was 0.6 microg/mL in plasma, and 0.48 microg/mL in urine. The standard curve was linear from 0.6 to 24 microg/mL in plasma, and 0.48 to 24 microg/mL in urine, both intra- and inter-day precision of the mangiferin were determined and their RSD did not exceed 10%. The method provides a technique for rapid analysis of mangiferin in rat plasma and urine, which can be used in pharmacokinetic studies.     

Development of a fluorimetric detection method for cinnabarinic acid using ortho‐tolyl hydrazine as the derivatization reagent

A fluorimetric detection method for one of the tryptophan metabolites, cinnabarinic acid (CA), which has recently been reported to have the ability to induce apoptosis in thymocytes, was developed using o‐tolyl hydrazine (TH) as the derivatization reagent. The carbonyl group at position 3 in CA was tagged with the hydrazino moiety of TH at 100°C for 30 min, and the generated derivative, CA tagged with TH, fluoresced at 412 nm with a 316 nm excitation wavelength. The CA tagged with TH was separated on a reversed‐phase HPLC and detected fluorometrically. The relative standard deviation was in the range of 1.1–8.9% (n = 3), and the detection limit was approximately 12?fmol (signal‐to‐noise ratio, 3). The proposed HPLC method can be useful for the sensitive detection of CA. Copyright © 2009 John Wiley & Son, Ltd.     

Development and validation of an LC-MS-MS method for determination of methyl kulonate in rat plasma

A sensitive, rapid and specific LC‐MS‐MS method was established and validated for determination of methyl kulonate, a major bioactive constituent isolated from Meliae Cortex, in rat plasma. Plasma samples were treated by precipitating protein with methanol and were chromatographed using a Capcell Pak C₁₈ column (100 × 4.6 mm, 5 µm) with the mobile phase comprising a mixture of methanol, 10 m m ammonium formate and formic acid (95:5:0.1, v/v/v). Detection and quantification were performed by mass spectrometry in the multiple reaction monitoring mode with positive atmospheric ionization at m/z 467 → 311 for methyl kulonate, and m/z 469 → 451 for dubione B (internal standard), respectively. A good linear response was observed over the concentration range 1.00–500 ng/mL with the lower limit of quantification 1.00 ng/mL in rat plasma. The method also afforded satisfactory results base on sensitivity, specificity, precision, accuracy, recovery, freeze–thaw and long‐time stability. The validated method was successfully applied to determine the pharmacokinetic properties of methyl kulonate in rats after oral administration at dose of 100 mg/kg. This pharmacokinetic study of methyl kulonate is reported here for the first time. Copyright © 2011 John Wiley & Sons, Ltd.     

Development of hollow fiber‐supported liquid‐phase microextraction and HPLC‐DAD method for the determination of pyrethroid metabolites in human and rat urine

A simple hollow fiber liquid‐phase microextraction method for the determination of synthetic pyrethroid metabolites, 3‐phenoxybenzoic acid and 4‐hydroxy‐3‐phenoxybenzoic acid, in human and rat urine was developed and validated. A polypropylene hollow fiber tightly fitted onto a Nylon rod and impregnated with organic solvent served as a disposable extraction device. Desorption of analytes was carried out in NaOH solution, analyzed further by gradient HPLC and diode array detection method. Important factors were identified using Taguchi OA16 (4⁵) orthogonal array design and further optimized using univariate approach. The optimum method performance was observed when 1 mL of urine hydrolyzed with 0.2 mL of concentrated HCl was further supplemented with 100 mg of NaCl and extracted for 120 min into dihexyl ether immobilized in the pores of the hollow fiber. Metabolites were desorbed into 0.1 mL of 0.1 M NaOH for another 120 min. Limits of detection and quantitation of 15 and 50 ng/mL were obtained for both analytes. Relative standard deviations of 1.6–12.6% over the linear range (50–10,000 ng/mL, r > 0.9906) were observed. Intra‐ and inter‐day accuracies of the method ranged from 98.3 to 109.5% and from 93.3 to 110.9%, respectively. The optimized method was applied to the analysis of real urine samples collected from rats exposed orally to cypermethrin. Copyright © 2013 John Wiley & Sons, Ltd.     

Simultaneous determination of N-benzylpiperazine and 1-(3-trifluoromethylphenyl)piperazine in rat plasma by HPLC-fluorescence detection and its application to monitoring of these drugs

An HPLC‐fluorescence detection method for simultaneous determination of N‐benzylpiperazine (BZP) and 1‐(3‐trifluoromethylphenyl)piperazine (TFMPP) labeled with 4‐(4,5‐diphenyl‐1 H‐imidazol‐2‐yl)benzoyl chloride (DIB‐Cl) was described. DIB‐BZP and ‐TFMPP were well separated within 13 min without interference of peaks from plasma components. The lower detection limits of BZP and TFMPP at a signal‐to‐noise ratio of 3 were 0.9 and 4.6 ng/mL, respectively. Precisions of the proposed method for intra‐ and inter‐day assays were less than 4.8 and 9.1% as %RSD (n = 5). Furthermore, the method could be successfully applied to monitor both compounds in plasma after their sole or co‐administration to rats (each dose, 2 mg/kg). Clearance of TFMPP was significantly different under the conditions (P = 0.047). Copyright © 2011 John Wiley & Sons, Ltd.