Simultaneous Quantitation of Paracetamol, Pseudoephedrine and Chlorpheniramine in Dog Plasma by LC-MS-MS

A simple, rapid and sensitive liquid chromatography/electrospray tandem mass spectrometry quantitative detection method, using amantadine as internal standard, was developed for the simultaneous analysis of paracetamol, pseudoephedrine and chlorpheniramine concentrations. Analytes were extracted from plasma samples by liquid–liquid extraction with n-hexane–dichloromethane–2-propanol (2:1:0.1, v/v), separated on a C18 reversed-phase column with 0.1% formic acid–methanol (40:60, v/v) and detected by electrospray ionization mass spectrometry in positive multiple reaction monitoring mode. Calibration curves for plasma were linear over the concentration range 10–10,000 ng mL^?1 of paracetamol, 2–2,000 ng mL^?1 of pseudoephedrine and 0.2–200 ng mL^?1 of chlorpheniramine. The method has a lower limit of quantitation of 10 ng mL^?1 for paracetamol, 2.0 ng mL^?1 for pseudoephedrine and 0.2 ng mL^?1 for chlorpheniramine. Recoveries, precision and accuracy results indicate that the method was reliable within the analytical range, and the use of the internal standard was very effective for reproducibility by LC-MS-MS. This method is feasible for the evaluation of pharmacokinetic profiles of a novel multicomponent sustained release formulation containing 325 mg of paracetamol, 30 mg of pseudoephedrine hydrochloride and 2 mg of chlorpheniramine maleate. It is the first time the pharmacokinetic evaluation of a novel sustained-action formulation containing paracetamol, pseudoephedrine and chlorpheniramine has been elucidated in vivo using LC-MS-MS.     

LC–ESI–MS Determination of Imperatorin in Rat Plasma After Oral Administration and Total Furocoumarins of Radix Angelica dahuricae and its Application to a Pharmacokinetic Study

A simple, rapid, sensitive and reliable liquid chromatography–electrospray ionization mass spectrometry method for the quantification of imperatorin in rat plasma after oral administration and total furocoumarins of Radix Angelica dahuricae has been established. The plasma samples were deproteinized by adding internal standard (IS) osthole solution, which was prepared by acetonitrile. The analysis was performed on a Shim-pack C₁₈ column (150 × 2.0 mm i.d., 5 μm) using acetonitrile and 0.5% formic acid solution (70:30, v/v) as a mobile phase. The detection was performed on a quadrupole mass spectrometer detector with an ESI interface operated in the selected ion monitoring mode. The linear quantification range of the method was 2–4000 ng mL^?1 in rat plasma with a correlation coefficient greater than 0.99, the limit of detection (LOD) was 0.5 ng mL^?1 and the lower limit of quantification (LLOQ) 2 ng mL^?1. The intra- and inter-day relative standard deviations (RSD) were less than 2.5 and 3.5%, respectively. The recoveries were above 90%. The validated method was successfully applied to a pharmacokinetic study of imperatorin in rats after oral administration and total furocoumarins of Radix Angelica dahuricae.     

GC Determination of Prilocaine HCl in Human Plasma: Analytical Application to Real Samples

A gas chromatographic (GC) method with a rapid and simple sample preparation was developed and validated for determination of prilocaine in human plasma. The validation parameters of linearity, precision, accuracy, recovery, specificity, limit of detection and limit of quantification were studied. The range of quantification for the GC method was 50–300 ng mL^?1 in plasma. Intra- and inter-day precision, expressed as the relative standard deviation (RSD) were less than 4.5%, and accuracy (relative error) was better than 8.0% (n = 6). The analytical recovery of prilocaine HCl from plasma has averaged 96.5% and the recovery of internal standard (lidocaine HCl) reached 96.8%. The limit of quantification (LOQ) and the limit of detection (LOD) of the method for plasma were 50 and 40 ng mL^?1, respectively. Also the developed and validated method was applied to three healthy volunteers to whom a local anaesthesia with citanest was administered.     

Simultaneous Determination of Amoxicillin and Clavulanic Acid in Dog Plasma by High-Performance Liquid Chromatography Tandem Mass Spectrometry

A rapid, sensitive, and specific high-performance liquid chromatography tandem mass spectrometric method was developed for the simultaneous determination and confirmation of amoxicillin and clavulanic acid in plasma. Plasma sample was subjected to a simple deproteinization with acetonitrile, and then the supernatant was directly diluted by water. Analysis was performed on a Phenomenex Luna C₈ reversed-phase column by detection with mass spectrometry in negative ions multiple reaction monitoring mode. A gradient elution program with 0.1% formic acid and acetonitrile was performed at a flow of 0.25 mL min^?1. There is good linearity in the range of 0.5–500 ng mL^?1 for both amoxicillin and clavulanic acid. The decision limits of amoxicillin and clavulanic acid were 0.06 ng mL^?1 and 0.08 ng mL^?1 in plasma, respectively, and the detection capabilities of two analytes were below 0.5 ng mL^?1. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The extraction recoveries of amoxicillin and clavulanic acid were between 102% and 115% in plasma at three spiked levels of 0.5, 50, and 500 ng mL^?1, with the relative standard deviations less than 15% for each analyte. The developed method was applied to pharmacokinetic studies of amoxicillin and clavulanic acid tablets in healthy beagles.     

Determination of Gastrodin and Ligustrazine Hydrochloride in Plasma and Brain Dialysate by LC–Tandem MS

A gradient liquid chromatography-tandem mass spectrometry method has been developed and validated for the determination of gastrodin and ligustrazine hydrochloride in rat plasma and brain dialysates. Zolpidem was used as internal standard. For plasma samples, solid-phase extraction was used and the brain dialysates were collected from freely moving rats using brain microdialysis. Both were followed by HPLC separation and positive electrospray ionization tandem mass spectrometry detection (ESI–MS–MS). Chromatographic separation was achieved on a Symmetry RP-18 column using gradient elution with methanol and water containing 0.5% formic acid and 2 mM ammonium formate. Selected reaction monitoring (SRM) mode was used for quantitation. Good linearities were obtained in the range of 0.05–100 and 0.01–50 μg mL^?1 for gastrodin and ligustrazine hydrochloride in rat plasma, and 0.05–1,000 ng mL^?1 for both in dialysate. The lower limit of quantitation was 0.01 ng mL^?1 for gastrodin and 0.05 ng mL^?1 for ligustrazine. The method is precise and reliable and can be applied to pharmacokinetic studies.     

Development and Validation of an Stability Indicating RP-LC Method for Determination of Imatinib Mesylate

A new, sensitive and stability indicating liquid chromatographic method has been developed for the determination of imatinib mesylate (IM). Efficient chromatographic separation was achieved using a C₁₈ column with simple mobile phase combination delivered in an isocratic mode and quantitation was carried out using ultraviolet detection. For the first time, a novel microwave assisted degradation procedure was employed for stress testing studies. In addition, orthogonal separation technique was applied to demonstrate selectivity of the proposed method. The method has demonstrated excellent linearity over the range of 25–1,600 ng mL^?1. Moreover, the method was found to be sensitive with a low limit of detection (3.35 ng mL^?1) and limit of quantitation (10.16 ng mL^?1). The method has shown good and consistent recoveries (99.35–100.69%) with low intra- and inter-day relative standard deviation (RSD) (<2.5%). Experimental design confirmed that peak area was unaffected by small changes in critical factors, in robustness study. The validated method was successfully applied for determination of IM in pharmaceutical formulations.     

Sensitive LC–ESI–MS Method for Determination of Tiopronin in Human Plasma

A sensitive liquid chromatographic–electrospray ionization–mass spectrometric (LC–MS) method has been developed for direct measurement of the concentration of tiopronin in human plasma. Hydrochloric acid solution was used to stabilize the tiopronin and prevent formation of a dimer, or reaction with endogenous thiols. The method involved liquid–liquid extraction of tiopronin from plasma samples with ethyl acetate, simple reversed-phase chromatography, and mass spectrometric detection with nanogram detection limits. Acetaminophen was used as internal standard (IS). The limit of quantification was 5 ng mL^?1 (RSD 4.3%). The method was validated within the linear range 5–500 ng mL^?1. The correlation coefficient for the calibration regression line was 0.9997 or better. Intra-day and inter-day accuracy were better than 15%. The method has been successfully used for a pharmacokinetic study with human subjects. Among the pharmacokinetic data obtained, t _1/2 was 2.37 ± 0.63 h and T _max was 4 h.     

Simultaneous Determination of Ritonavir and Lopinavir in Human Plasma after Protein Precipitation and LC-MS-MS

A simple, rapid, specific and sensitive method has been developed and validated for simultaneous determination of lopinavir and ritonavir in human plasma. The analytical procedure involves a protein precipitation method using fluoxetine as internal standard Separation was carried out on an Inertsil ODS column using a mobile phase consisting of acetonitrile and 5 mM ammonium acetate buffer. The total run time of analysis was 2.0 min. A linear response function was established for the range of concentrations 50.67–10,008.82 ng mL^?1 for lopinavir and 5.066–1,000.693 ng mL^?1 for ritonavir. The method was successfully applied to an oral bioequivalence study in humans.     

LC–MS–MS Analysis of Strictosamide in Rat Plasma, and Application of the Method to a Pharmacokinetic Study

A rapid and simple high-performance liquid chromatographic tandem mass spectrometric method has been developed and validated for analysis of strictosamide in rat plasma. Chromatographic separation was achieved on a C₁₈ column by gradient elution with mixtures of methanol, water, and acetonitrile containing 0.05% acetic acid. Digoxin was used as internal standard. Selected reaction monitoring (SRM) was used for MS quantitation. Linearity was good in the range 0.05–20 ng mL^?1 in rat plasma. The lower limit of quantitation was 0.04 ng mL^?1. The method is precise and reliable and can be applied to pharmacokinetic studies.     

LC-MS–MS Determination of Pregabalin in Human Plasma

A rapid, sensitive and specific method to quantify pregabalin in human plasma using metaxalone as the internal standard is described. Sample preparation involved simple protein precipitation by using acetronitrile as solvent. The extract was analyzed by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (LC-MS–MS). Chromatography was performed isocratically on Thermo Hypurity C₁₈ 5 μm analytical column, (50 mm × 4.6 mm i.d.). The assay of pegabalin was linear calibration curve over the range 10.000–10000.000 ng mL^?1. The lower limit of quantification was 10.000 ng mL^?1 in plasma. The method was successfully applied to the bioequivalence study of pregabalin capsules (150.0 mg) administered as a single oral dose.     

HPLC Determination of Letrozole in Plasma Using Fluorescence Detection: Application to Pharmacokinetic Studies

A simple, rapid and sensitive HPLC method has been developed and validated for the analysis of letrozole in human plasma. The separation was achieved on a monolithic silica column using acetonitrile–phosphate buffer. A fluorescence detector was used for the quantitation with excitation and emission wavelengths at 230 and 295 nm. The assay enables the measurement of letrozole for therapeutic drug monitoring with a minimum quantification limit (LOQ) of 0.5 ng mL^?1. The method involves a simple, one-step extraction procedure with complete recovery. Calibration was linear over the concentration range 0.5–80 ng mL^?1. The coefficients of variation for inter-day and intra-day assay were found to be less than 8%.     

Development and Validation of LC-UV for Simultaneous Estimation of Rosiglitazone and Glimepride in Human Plasma

A simple, sensitive and specific liquid chromatographic method with UV detection (228 nm) was developed for the simultaneous estimation of rosiglitazone and glimepride in human plasma. Rosiglitazone and glimepride were extracted from plasma using liquid–liquid extraction. Separation was achieved with an RP C₁₈ Column using a mixture of phosphate buffer (50 mM) with octane sulfonic acid (10 mM), methanol and acetonitrile as a mobile phase (55:10:35, v/v). pH was adjusted to 7.0. Amlodipine was used as an internal standard (IS). LOD of the method was found to be 20 ng mL^?1 for both drugs. Results were linear over the studied range 40.994–2007.556 ng mL^?1 for rosiglitazone (r ² ≥ 0.99) and 41.066–2094.84 ng mL^?1 for glimepride( r ² ≥ 0.99). The method was found to be simple, selective, precise and reproducible for the estimation of both drugs from spiked human plasma.     

Quantification of Tacrolimus in Human Skin Samples and Ointment by LC-MS

A sensitive and simple liquid chromatography-mass spectrometry method was developed to determine the immunosuppressant tacrolimus in human skin samples after treatment with the commercially available ointment. Utilizing diffusion cell experiments according to Franz, human skin samples were treated with ointment containing tacrolimus and the extraction procedure of the drug was optimized. The analytical assay was performed using an LC system consisting of a reversed phase C₁₈ column and an isocratic mobile phase, coupled with electrospray ionization mass spectrometry. The detection was performed in the positive selected ion monitoring mode. Mycophenolate mofetil was used as internal standard to control the stability of the electrospray ionization. The calibration curve was linear for tacrolimus over the range of 5–1,000 ng mL^?1 (average correlation coefficient of r ² = 0.9941) with a limit of detection (LOD) of 2 ng mL^?1, with a limit of quantification (LOQ) of 5 ng mL^?1 and with a precision of 8.70%. The analytical assay described in this paper was successfully applied in order to quantify tacrolimus in human skin samples as well as in the commercially available ointment.     

Simultaneous LC–MS Analysis and of Wogonin and Oroxylin A in Rat Plasma, and Pharmacokinetic Studies After Administration of the Active Fraction from Xiao-Xu-Ming Decoction

A rapid and specific high-performance liquid chromatographic method coupled with electrospray ionization mass spectrometric detection has been developed and validated for identification and quantification of wogonin and oroxylin A in rat plasma. Wogonin, oroxylin A, and diazepam (internal standard) were extracted from plasma samples by liquid–liquid extraction with ethyl acetate. Chromatographic separation was achieved on a C₁₈ column with acetonitrile–0.6% aqueous formic acid 35:65 (v/v) as mobile phase at a flow rate of 0.2 mL min^?1. Detection was performed with a single-quadrupole mass spectrometer in selected-ion-monitoring (SIM) mode. Linearity was good within the concentration range 14.4–360 ng mL^?1 for wogonin and 10.8–271 ng mL^?1 for oroxylin A; the correlation coefficients (r ²) were 0.9999. The intra-day and inter-day precision, as RSD, was below 12.4%, and accuracy ranged from 81.1 to 111.9%. The lower limit of quantification was 14.4 ng mL^?1 for wogonin and 10.8 ng mL^?1 for oroxylin A. This method was successfully used in the first pharmacokinetic study of wogonin and oroxylin A in rat plasma after oral administration of the active fraction from Xiao-xu-ming decoction.     

Quantitative Determination of Phillyrin in Human Plasma Using HPLC with Fluorescence Detection

A simple, rapid, and selective high-performance liquid chromatography method for determination of phillyrin in human plasma was developed. After extracting from the plasma samples with ethyl acetate, the analyte was chromatographed on a C18 column with methanol–water (50:50, v/v, pH 2.86) as mobile phase. The fluorescence excitation and emission wavelengths were 277 and 315 nm, respectively. The linear range of the standard curve of phillyrin was 0.0313–8.0 μg mL^?1 (r > 0.999). The limit of detection was 6.31 ng mL^?1. The average recovery of phillyrin was 101.02% from plasma. The intra- and inter-day variabilities of phillyrin were <10.00%.     

RP-LC Determination and Pharmacokinetic Study of Ferulic Acid and Isoferulic Acid in Rat Plasma After Taking Traditional Chinese Medicinal-Preparation: Guanxinning Lyophilizer

A sensitive, simple, and accurate method for determination and pharmacokinetic study of ferulic acid and isoferulic acid in rat plasma was developed using a reversed-phase column liquid chromatographic (RP-LC) method with UV detection. Sample preparations were carried out by protein precipitation with the addition of methanol, followed by evaporation to dryness. The resultant residue was then reconstituted in mobile phase and injected into a Kromasil C₁₈ column (250 × 4.6 mm i.d. with 5 μm particle size). The mobile phase was methanol-1% formic acid (33:67, v/v). The calibration plots were linear over the range 5.780–5780 ng·mL^?1 for ferulic acid and 1.740–348.0 ng·mL^?1 for isoferulic acid. Mean recoveries were 85.1% and 91.1%, respectively. The relative standard deviations (RSDs) of within-day and between-day precision were not above 15% for both of the analytes. The limits of quantification were 5.780 ng·mL^?1 for ferulic acid and 1.740 ng·mL^?1 for isoferulic acid. This RP-LC method was used successfully in pharmacokinetic studies of ferulic acid and isoferulic acid in rat plasma after intravenous injection of Guanxinning Lyophilizer.     

Optimization of Continuous Flow Hydride Generation Inductively Coupled Plasma Optical Emission Spectrometry for Sensitivity Improvement of Bismuth

Experimental variables in continuous flow hydride generation inductively coupled plasma-optical emission spectrometry (CF-HG-ICP-OES) were optimized for determination of bismuth. Concentrations of NaBH₄, HCl, and NaOH, flow rates of NaBH₄, sample solution, waste and carrier argon, radio frequency power, lengths of reaction, and stripping coils were optimized to obtain lower detection limits. Under optimum conditions, the detection limit was calculated as 0.16 ng mL^?1, and the calibration plot was linear between 1.0–50.0 ng mL^?1. An improvement in detection limit of 5.75 times by CF-HG-ICP-OES was reached vs. ICP-OES. Relative standard deviation (RSD) for ten replicate measurements of 10.0 ng mL^?1 Bi was calculated as 3.9%. Effect of possible interferic ions on Bi signal was evaluated. Accuracy of method was verified by using a standard reference material, SRM 1643e. Results found for Bi were in satisfactory agreement with certified values. The proposed method was then employed to determine trace concentration of Bi in milk samples. Bi amounts in samples were found in the range from lower than the quantitation limit to 14.5 ng mL^?1, whereas Bi concentrations were lower than the detection limit in three samples.     

Chemiluminometric Determination of the Pesticide Pirimicarb by a Flow Injection Analysis Assembly

Abstract

A flow injection (FI) method is described for the determination of pirimicarb. It was found that an enhanced chemiluminescence (CL) signal is obtained when employing the luminol–H₂O₂–horseradish peroxidase (HRP) system. Under the optimum experimental conditions, the enhanced CL intensity was linear with the concentration 4.25–30.75 ng mL^?1 (r = 0.997, n = 8) with a relative standard deviation of 0.99%, containing 12.75 ng mL^?1 (n = 8). The limit of detection of the investigated compound was 0.12 ng mL^?1. The method shows a moderate selectivity against other pesticides (Amitrole, Atrazine, 2,4,5-T, Dichlorprop, and Metamidophos).The proposed method was sensitive, simple, rapid, and successfully applied to the determination of pirimicarb when it is applied in freshwater; the mean recoveries were 98.3–118.5%.     

Quantitative Analysis of Sertraline in Human Serum by LC with Fluorescence Detection After Pre-Column Derivatization with 4-Chloro-7-nitrobenzofurazan

An accurate and sensitive reversed-phase high-performance liquid chromatographic method for analysis of sertraline in human serum, using 4-chloro-7-nitrobenzofurazan as pre-column derivatization agent, is described. The drug and an internal standard (azithromycin) were extracted from serum by use of a mixture of diethyl ether and chloroform, and subjected to pre-column derivatization with the reagent. Analysis of the resulting derivatives was performed on a 250 mm × 4.0 mm cyano column with 63:37 (v/v) methanol–sodium phosphate buffer (0.05 M, pH 3.7) containing 2 mL L^?1 triethylamine as mobile phase. Detector response was monitored at excitation and emission wavelengths of 470 and 537 nm, respectively. The calibration plot was linear over the concentration range 2–640 ng mL^?1. The lower limits of detection and quantification were 0.5 and 2 ng mL^?1, respectively. The method was validated for specificity, sensitivity, linearity, precision, accuracy, and stability and shown to be accurate (intra-day and inter-day accuracy from 0.3 to 4.2%) and precise (intra-day and inter-day precision from 2.4 to 15.5%). The drug was detected at concentrations as low as 2 ng mL^?1 in 0.5 mL serum and the method described can be easily applied to human single-dose pharmacokinetic studies of sertraline.     

Online Purification and Screening of Nisoldipine with a Novel Poly(vinyl ester) Resin Monolithic Column

A monolithic column, prepared from a vinyl ester resin used as both monomer and cross-linking agent, has been used to remove matrix compounds from biological fluid. Using this column, nisoldipine in human plasma samples could be enriched online and the protein could be eluted. For this method of extraction, response (peak area) was a linear function of concentration in the range 2–80 ng mL^?1, with a linear regression coefficient of 0.99985. The limit of detection for nisoldipine in plasma was 1.2 ng mL^?1. For nisoldipine at concentrations of 10, 30, and 70 ng mL^?1 RSD were 4.33, 6.63, and 4.57%, respectively. Recovery for both extraction (>73.6%) and the entire analytical method (>90.7%) were acceptable for screening of plasma for nisoldipine. The 12-hour pharmacokinetic profile of nisoldipine in mice after oral administration (0.3 mg kg^?1) was investigated. The results indicated the method could be used for therapeutic monitoring of nisoldipine and enabled simple and rapid assay of the drug in plasma.