LC�CMS�CMS Quantitative Determination of Brivudine in Human Plasma and Its Application to Pharmacokinetic Studies

A sensitive and specific liquid chromatography?Celectrospray ionization?Ctandem mass spectrometry method has been developed and validated for the identification and quantification of brivudine in human plasma using diclofenac as an internal standard. The method involves extraction with ethyl acetate. The analyte was separated on a C₁₈ column and analyzed in multiple reaction monitoring mode with a negative electrospray ionization interface using the [M?CH]^? ions, m/z 332.8??m/z 80.9 for brivudine, m/z 293.6??m/z 249.5 for diclofenac. The method was validated over the concentration range of 5.54?C2,836 ??g L^?1 for brivudine. The intra-and inter-day precisions were less than 8.91% in terms of relative standard deviation (RSD), and the accuracy was within ?4.22% in terms of relative error (RE). The lower limit of quantification (LLOQ) was 5.54 ??g L^?1 with acceptable precision and accuracy. There were almost no matrix effects. Recovery of brivudine spiked in drug-free plasma was higher than 77.17%. The method was used to study the pharmacokinetic profile of brivudine in human plasma after oral administration of brivudine tablets.     

Determination of Pilocarpine in Human Plasma by LC�CAPCI�CMS�CMS and Application to a Pharmacokinetic Study

A sensitive, specific and rapid high performance liquid chromatography?Catmospheric pressure chemical ionization source-tandem mass spectrometry (LC-APCI-MS-MS) method for the determination of pilocarpine in human plasma was developed and validated. The method is based on liquid?Cliquid extraction, followed by a reversed-phase liquid chromatographic separation, and detected by means of tandem mass spectrometry. The linear calibration curve covered a concentration range of 2?C500 ??g L^?1. The intra- and inter-day precisions for pilocarpine were <10% and the accuracies were between 90 and 110%. The method was applied successfully to a pharmacokinetic study involving 20 healthy Chinese male volunteers after oral administration of 6 mg pilocarpine.     

Determination of Amphotericin B in Human Cerebrospinal Fluid by LC–MS–MS

A simple, specific and sensitive column liquid chromatography–tandem mass spectrometry method has been developed for the determination of amphotericin B in human cerebrospinal fluid. Samples were prepared by dilution with methanol and quantitated by MS–MS detection in the positive mode. The determination was validated in the concentration range of 0.5–100 ng mL^?1 using 100 μL of human cerebrospinal fluid. The method was successfully used to support routine therapeutic drug monitoring.     

Determination of Revaprazan in Human Plasma by LC�CMS�CMS and Application to a Pharmacokinetic Study in Chinese Volunteers

A sensitive, specific, and rapid liquid chromatography?Celectrospray ionization?Ctandem mass spectrometry (LC?CESI?CMS?CMS) method was developed for determination of revaprazan in human plasma. Plasma samples were simply treated with methanol to precipitate, and then isolated supernatants were directly injected into the LC?CESI?CMS?CMS system. A Thermo Hypurity C18 column (150 × 2.1 mm, 5 ??m) with mobile phase of methanol?Cwater (70:30, v/v) containing 0.05% formic acid was used for chromatographic separation. Mass-spectrometric quantification was carried out in multiple reaction monitoring (MRM) mode, monitoring the m/z transitions 363.1 ?? 245.1 for revaprazan and 531.2 ?? 489.2 for ketoconazole (internal standard, IS) in positive ion mode. The linear calibration curves covered a concentration range of 2?C1,000 ??g L^?1. The intra- and interday precisions (percentage relative standard deviation, RSD%) for revaprazan at three quality control levels were all <5%, and the accuracies were between 90% and 110%. The method has been successfully applied to a pharmacokinetic study involving 12 Chinese volunteers, and the main pharmacokinetic parameters of revaprazan in Chinese population are reported for the first time.     

Rapid Simultaneous Determination of Eight Benzimidazoles in Animal Feed by LC�CMS�CMS

A rapid, sensitive and reliable LC?CMS?CMS method for the determination of eight benzimidazoles in animal feed was developed and validated. Samples were extracted with acidic acetonitrile. The extract was diluted with 0.1% formic acid in water, and analyzed by LC?CMS?CMS on a Waters XBridge? C₁₈ column with acetonitrile/0.1% formic acid in water as mobile phase. The samples were quantified with the matrix standard calibration curve method. Good linearity was obtained for eight benzimidazoles at a concentration of 0.005?C2.5 ??g mL^?1 with a linear relative coefficient more than 0.990. Recoveries of 84.0?C104.0% with CVs of 2.50?C7.50% were obtained. Limit of detection was 2.1?C63.0 ??g kg^?1. The method demonstrated to be suitable for the determination of eight benzimidazoles in animal feed samples.     

Simultaneous Determination of Hydrocodone, and Its Two Metabolites in Human Plasma by HPLC�CMS�CMS

A rapid, sensitive and specific assay method has been developed to simultaneously determine human plasma concentrations of hydrocodone and its metabolites, norhydrocodone, hydromorphone, using high-performance liquid chromatography with an electrospray ionization (ESI) tandem mass spectrometry (HPLC?CMS?CMS). Hydrocodone, its metabolites, and internal standard, hydrocodone-d ₃, norhydrocodone-d ₃, hydromorphone-d ₃, were separated from human plasma using solid-phase extraction (Empore MPC-SD Solid Phase Extraction Disk). The eluate was dried, reconstituted and injected into the LC?CMS?CMS system. Chromatographic separation was performed on a Kromasil 100-5SIL-Dimensions C₁₈ column (100 × 2.1 mm, 5.0 ??m, Thermo Hypersil-Keystone, USA) using a gradient mobile phase with 20 mmol L^?1 ammonium formate in water with 0.2% formic acid and 0.1% formic acid in acetonitrile. Detection and quantitation were performed by MS/MS using electrospray ionization and multiple reactions monitoring in the positive ion mode. The calibration curves were linear over the concentration ranges 0.05?C50 ng mL^?1 for hydrocodone (r ² = 0.9991) and norhydrocodone (r ² = 0.9990), and 0.01?C10 ng mL^?1 for hydromorphone (r ² = 0.9990). The limit of quantification was 0.05 ng mL^?1 for hydrocodone and norhydrocodone, and 0.01 ng mL^?1 for hydromorphone. The extraction recovery was above 64.36, 68.51 and 71.78% for hydrocodone, norhydrocodone and hydromorphone. The accuracy was higher than 99.06, 97.70 and 100.07% for hydrocodone, norhydrocodone and hydromorphone. The intra- and inter-day precisions were <5.80, 5.90 and 3.02% for hydrocodone, norhydrocodone and hydromorphone. The method was accurate, sensitive and simple and was successfully applied to a pharmacokinetic study after a single oral administration of hydrocodone bitartrate at a dose of 5 mg in 12 healthy Chinese volunteers.     

Rapid and Simultaneous Determination of Efavirenz, 8-Hydroxyefavirenz, and 8,14-Dihydroxyefavirenz Using LC�CMS�CMS in Human Plasma and Application to Pharmacokinetics in Healthy Volunteers

We developed a rapid and sensitive method for determining efavirenz, 8-hydroxyefavirenz, and 8,14-dihydroxyefavirenz in human plasma simultaneously using liquid chromatography?Ctandem mass spectrometry (LC?CMS?CMS). Three compounds and ritonavir, an internal standard, were extracted from plasma using ethyl acetate in the presence of 0.1 M sodium carbonate after incubation of ??-glucuronidase (500 U). After drying the organic layer, the residue was reconstituted in mobile phase (acetonitrile:20 mM ammonium acetate, 90:10, v/v) and injected onto a reversed-phase C₁₈ column. The isocratic mobile phase was eluted at 0.2 mL min^?1. The ion transitions monitored in multiple reaction-monitoring mode were m/z 314 ?? 244, 330 ?? 258, 346 ?? 262, and 721 ?? 296 for efavirenz, 8-hydroxyefavirenz, 8,14-dihydroxyefavirenz, and ritonavir, respectively. The retention time is 1.93, 1.70, 1.52, and 1.82 min for efavirenz, 8-hydroxyefavirenz, 8,14-dihydroxyefavirenz, and ritonavir, respectively. The coefficients of variation of the assay precision were less than 10.7%, and the accuracy was 90?C111%. The lower limits of quantification (LLOQ) were 5 ng mL^?1 for efavirenz and 8-hydroxyefavirenz. This method was used to measure the plasma concentrations of efavirenz and its metabolites from healthy volunteers after a single 600 mg oral dose of efavirenz. This analytical method is a very rapid, sensitive, and accurate to determine the pharmacokinetic profiles of efavirenz including its metabolites.     

Analysis of Fluoroquinolones in Animal Feed Based on Microwave-Assisted Extraction by LC�CMS�CMS Determination

An environmentally friendly method for the determination of fluoroquinolone (FQ) antibiotics including enrofloxacin, ciprofloxacin, levofloxacin, fleroxacin and sparfloxacin in four feeds is proposed. Disodium ethylenediaminetetraacetate (EDTA)?CMcllvaine buffer (0.1 mol L^?1, pH 4.0) was used as an extracting solvent and the extraction process was accelerated by microwave irradiation. No organic solvents were used in the extraction procedure. The extract obtained was then cleaned up and concentrated by an Oasis hydrophilic?Clipophilic balance (HLB) solid-phase extraction cartridge. The relative intra- and inter-day standard deviations obtained were in the range of 3.7?C9.1 and 2.1?C11.4%, respectively. In the three fortified levels of blank feed sample (30, 100 and 500 ng g^?1), recoveries of FQs ranging from 61.1 to 97.9% were obtained. The analytes desorbed from HLB were analyzed by liquid chromatography?Ctandem mass spectrometry. The limit of detection was in the range of 5.0?C9.1 ng g^?1. The method presented here can be considered a promising alternative to traditional techniques using shaking or stirring for extraction, being more effective, and producing less pollution.     

Determination of Quinine and Doxycycline in Rat Plasma by LC�CMS�CMS: Application to a Pharmacokinetic Study

A fast, sensitive, and specific LC?CMS?CMS method for determination of quinine (QN) and doxycycline (DOX) in rat plasma has been developed and validated. QN, DOX, and cimetidine (internal standard, IS) were extracted from the plasma by protein precipitation. The compounds were separated on a C₁₈ column with methanol?C0.1% aqueous formic acid 70:30 (v/v) as mobile phase at a flow rate of 0.5 mL min^?1 (split 1:3). Detection was by positive electrospray ionization (ESI+) in multiple reaction monitoring (MRM) mode, monitoring the transitions 325.0 ?? 307.0, 445.0 ?? 428.1, and 252.8 ?? 159.0, for QN, DOX, and IS, respectively. The analysis was carried out in 2.0 min and the method was linear in the plasma concentration range 5?C5,000 ng mL^?1. The mean extraction recoveries for QN, DOX, and IS from plasma were 89.4, 90.5, and 86.3%, respectively. The method was validated for linearity, precision, accuracy, specificity, and stability; the results obtained were within the acceptable range. The proposed method was successfully applied to the determination of QN and DOX in rat plasma samples to support pharmacokinetic studies.     

Determination of Fulvestrant in Rat Plasma by LC�CMS�CMS: Application to a Pharmacokinetic Study

A reversed-phase liquid chromatography coupled to tandem mass spectrometry (LC?CMS?CMS) method was developed and validated for the determination of fulvestrant in rat plasma. Sample preparation involved a liquid-liquid extraction using 1.0 mL of n-hexane?Cisopropanol (90:10, v/v) to extract the analyte from 0.1 mL of rat plasma. The analytes were separated on a phenyl-based column using the mobile phase consisting of methanol/water containing 5 mM ammonium acetate at the flow rate of 0.3 mL min^?1. The analytes were monitored by tandem mass spectrometry under electrospray negative ionization mode. Linear calibration curves were generated over the fulvestrant concentration ranges of 0.05?C10.0 ng mL^?1 in rat plasma. The accuracy and within- and between-day precisions were within the generally accepted criteria for bioanalytical methods (<15%). This developed and validated assay method was successfully employed to characterize the plasma concentration-time profile of fulvestrant after its intramuscular administration in rats at a dose of 10 mg kg^?1.     

LC–MS–MS Determination of Rotenone, Deguelin, and Rotenolone in Human Serum

For the first time we report a rapid and sensitive LC–MS–MS method for quantification of rotenone, deguelin, and rotenolone in human serum. The analytical procedure involves extraction with ethyl acetate without further clean-up. The active ingredients were separated on a C₈ reversed-phase column by isocratic elution. Eleven simultaneous transitions of precursor ions were monitored. Excellent selectivity and sensitivity enables quantification and identification of low levels of rotenoids (LOD 2 ng mL^?1, LOQ 5 ng mL^?1) in human serum.     

Simultaneous Determination of Pregabalin, Sildenafil and Its Active Metabolite in Rat Plasma Utilising SPE Followed by LC�CMS�CMS

A sensitive and selective analytical method for the quantification of pregabalin, sildenafil and the active desmethyl metabolite of sildenafil (UK-103320) has been developed. The method can simultaneously quantify the three analytes within the expected in vivo concentration ranges using 50 ??L of rat plasma. It utilises solid-phase extraction followed by high performance liquid chromatography coupled with tandem mass spectrometry. Quantitation in rat plasma demonstrated good accuracy and precision over the following dynamic ranges for each analyte: pregabalin (70?C10,000 ng mL^?1), sildenafil (1?C2,000 ng mL^?1) and UK-103320 (1?C2,000 ng mL^?1). For each analyte, the following lower limits of quantitation were obtained: 70 ng mL^?1 for pregabalin and 1 ng mL^?1 for sildenafil and UK-103320, respectively. The method was successfully used to analyse plasma samples from rats when pregabalin and sildenafil were administered in combination.     

Uncertainty Analysis of Chlormequat Residue in Fruits by LC�CMS�CMS

A method for determination of chlormequat (CCC) residue in fruits by liquid chromatography?Ctandem mass spectrometry (LC?CMS?CMS) was developed. Residue of CCC was extracted from samples with methanol?Cwater (v/v, 1:1) containing 1.0% acetic acid, cleaned up by strong cationic exchange (SCX) cartridge, and then determined by LC?CMS?CMS. The method showed good linearity over the concentration range 0.002?C5.0 mg kg^?1 with correlation coefficient above 0.997. The limit of detection (LOD) and limit of quantitation (LOQ) for CCC were 5 × 10^?4 mg kg^?1 (S/N = 3) and 0.002 mg kg^?1 (S/N = 10), respectively. Recoveries for CCC at three spiked levels (0.025, 0.050, and 0.20 mg kg^?1) were in the range 80?C102%. Estimation of measurement uncertainty was calculated for CCC at the level of 0.025 mg kg^?1 in fruits. The results demonstrated that the uncertainty of recovery was the main contribution to the combined standard uncertainty. The relative combined standard uncertainties associated with the method ranged from 11 to 13%, depending on the sample matrices.     

HPLC�CMS�CMS for the Simultaneous Determination of Atorvastatin and Amlodipine in Plasma of Hypertensive Patients

Combination drug products containing amlodipine and atorvastatin are widely marketed and used in the treatment of concomitant hypertension and dyslipidemia. A rapid, simple and sensitive high performance liquid chromatography?Ctandem mass spectrometry (HPLC?CMS?CMS) method for determination of atorvastatin and amlodipine in plasma of hypertensive patients has been developed and validated to be used for therapeutic drug monitoring. The plasma samples were subjected to methanol protein precipitation. Chromatographic separation was performed on a C18 column using a gradient elution. The mobile phase consisted of 0.1% of formic acid in water and 0.1% of formic acid in acetonitrile and was pumped at a flow rate of 0.4 mL min^?1. Detection of analytes was achieved by tandem mass spectrometry with electrospray ionization (ESI) interface in positive ion mode. The calibration curves were linear over the range of 0.46?C1,000 ng mL^?1. The intra- and inter-day precisions were within 12.2%, while the accuracy ranged from 92.7 to 108.1%. The validated LC?CMS?CMS method was successfully applied for the determination of atorvastatin and amlodipine in plasma of hypertensive patients.     

Rapid and Selective LC�CMS�CMS Method for the Determination of cyclo-trans-4-l-Hydroxyprolyl-l-serine (JBP485) in Rat Plasma

A rapid and selective liquid chromatographic/tandem mass spectrometric method for the determination of JBP485 was developed and validated. Following protein precipitation, the analyte and internal standard (JBP923) were separated from human plasma using an isocratic mobile phase on an Elite Kromasil C18 column. An API 3200 tandem mass spectrometer equipped with a Turbo ionSpray ionization source was used as the detector and operated in the positive ion mode. Multiple reaction monitoring using the precursor to product ion combinations of m/z 201.2 ?? 86.2 and m/z 219.2 ?? 86.2 was performed to quantify JBP485 and JBP923, respectively. The method was linear in the concentration range of 0.10?C50.00 ??g mL^?1 using 100 ??L of plasma. The lower limit of quantification was 0.10 ??g mL^?1. The intra- and inter-day relative standard deviations over the entire concentration range were less than 6.65%. Accuracy determined at three concentrations (0.25, 4.00 and 25.00 ??g mL^?1 for JBP485) ranged from ?0.78 to 2.74% in terms of relative error. Each plasma sample was chromatographed within 2.0 min. The method was successfully applied to characterize the pharmacokinetic profiles of JBP485 in rats after an intravenous injection of 6.25 mg kg^?1 JBP485.     

Determination of Imidol in Rat Plasma by UPLC�CMS�CMS and Its Application in a Pharmacokinetic Study

A rapid, sensitive and accurate ultra-performance liquid chromatography/tandem mass spectrometry method was developed and validated for the quantitative determination of imidol in rat plasma for the first time. The analyte and internal standard were extracted from plasma by liquid?Cliquid extraction with diethyl ether. The separation was performed on a BEH C₁₈ column (50 mm × 2.1 mm, 1.7 ??m). The detection was carried out by electrospray ionization mass spectrometry in positive ion mode with multiple reaction monitoring. Linear calibration curves were obtained in the concentration range of 2.5?C2,500 ng mL^?1, with the lower limit of quantification of 2.5 ng mL^?1. The intra- and inter-day precision (RSD) values were below 8% and accuracy (RE) was from ?7.9 to 6.3%. After strict validation, the method was applied successfully to the pharmacokinetic study of imidol in rats after oral and intravenous administration, respectively.     

Simultaneous Determination of Pethidine and Atropine in Rabbit Plasma by LC�CMS�CMS and Its Application to a Pharmacokinetic Study after Intramuscular Administration

A sensitive and selective liquid chromatography?Ctandem mass spectrometry method for the determination of pethidine and atropine in rabbit plasma was developed and validated. The analytes and internal standard (IS) are extracted from plasma by liquid?Cliquid extraction using ethyl acetate, and separated on a Zorbax SB-Aq column (2.1 × 150 mm, 3.5 ??m) using acetonitrile?C0.1% formic acid as mobile phase with gradient elution. Electrospray ionization source was applied and operated in positive ion mode, and multiple reaction monitoring mode was used for quantification using target fragment ions m/z 247.8 ?? 219.7 for pethidine, m/z 289.9 ?? 123.8 for atropine and m/z 295.0 ?? 266.8 for IS, respectively. The assay is linear over the range of 5?C1,000 ng mL^?1 for pethidine and atropine, with a lower limit of quantification of 3 ng mL^?1 for pethidine and 5 ng mL^?1 for atropine. Intra-day and inter-day precision are less than 11% and the accuracy are in the range of 90.4?C106.3%. Furthermore, the newly developed method is successfully used for the determination of pethidine and atropine in rabbit plasma for pharmacokinetic study.     

LC�CMS Analysis of Sertraline and Its Active Metabolite in Human Serum Using a Silica Column with a Non-Aqueous Polar Mobile Phase

A sensitive liquid chromatography?Cmass spectrometry method for the simultaneous determination of sertraline (SER) and its major metabolite norsertraline (NOR) from serum was developed and validated in the context of a pharmacokinetic study in pregnant women. The separations were achieved on a silica column with a non-aqueous polar mobile phase consisting of acetonitrile, methanol and ammonium acetate at a flow rate of 0.5 mL min^?1. The concentrations were measured using a single quadruple mass spectroscopic detector supplied with atmospheric pressure ionization electrospray. Sample preparation consisted of a simple liquid?Cliquid procedure. The detector was set in selective ion mode for each compound of interest, 306 m/z for SER and 275 m/z for NOR. Calibration curves were generated by least square linear regression for concentration of 5?C160 ng mL^?1 for SER and from 10 to 320 ng mL^?1 for NOR. The curves for both compounds of interest were linear, with correlation coefficients r ² ?? 0.999.     

On-Line SPE Coupled with LC�CAPCI�CMS for the Determination of Trace Explosives in Water

In this study, a rapid, sensitive, and fully automated on-line solid phase extraction (SPE)?Cliquid chromatography (LC)?Cmass spectrometry (MS) method for the analysis of explosive residues in water, was systematically investigated. First, separation of explosive residues was achieved by reverse-phase chromatography using an XDB-C18 column in 30 min with an eluent containing 0.1% acetic acid, 5 mM ammonium acetate, and methanol. Secondly, atmospheric pressures chemical ionization (APCI) and electrospray ionization (ESI) interfaced with the MS detector were used to examine the explosive residues, indicating that APCI?CMS was more suitable than ESI?CMS for the detection of explosives. Thirdly, the conditions for on-line SPE, including solvent pH and sample injected volume, were optimized. The calibration curves obtained for all explosives studied were linear in the concentration range 0.5?C50 ??g L^?1. The detection limits of this method ranged from 0.05 to 0.5 ??g L^?1 when 4000 ??L of sample was on-line pre-concentrated on C18 enrichment column. The recoveries from lake waters spiked with explosive standard solution ranged from 90.5 to 108.0%. The proposed method is simple, fast, and could be applied successfully to the analysis of explosive residues in contaminated water without any further pretreatment.     

GC�CMS and GC�CNPD Determination of Formaldehyde Dimethylhydrazone in Water Using SPME

Formaldehyde dimethylhydrazone (FADMH) is one of the important transformation products of residual rocket fuel 1,1-dimethylhydrazine (1,1-DMH). Thus, recent studies show that FADMH toxicity is comparable to that of undecomposed 1,1-DMH. In this study, a new method for quantification of FADMH in water based on solid phase microextraction (SPME) in combination with gas chromatography (GC) with mass spectrometric (MS) and nitrogen-phosphorus detection (NPD) is presented. Effects of SPME fiber coating type, extraction and desorption temperatures, extraction time, and pH on analyte recovery were studied. The optimized method used 65 micron polydimethylsiloxane/divinylbenzene fiber coating for 1?min headspace extractions at 30?°C. Preferred pH and desorption temperature from the SPME fiber are >8.5 and 200?°C, respectively. Detection limits were estimated to be 1.5 and 0.5?μg?L(-1) for MS and NPD, respectively. The method was applied to laboratory-scale experiments to quantify FADMH. Results indicate applicability for in situ sampling and analysis and possible first-time detection of free FADMH in water.