The “Other” Inositols and Their Phosphates: Synthesis,Biology, and Medicine (with Recent Advances in myo‐Inositol Chemistry)

Cell signaling via inositol phosphates, in particular via the second messenger myo‐inositol 1,4,5‐trisphosphate, and phosphoinositides comprises a huge field of biology. Of the nine 1,2,3,4,5,6‐cyclohexanehexol isomers, myo‐inositol is pre‐eminent, with “other” inositols (cis‐, epi‐, allo‐, muco‐, neo‐, l ‐chiro‐, d ‐chiro‐, and scyllo‐) and derivatives rarer or thought not to exist in nature. However, neo‐ and d ‐chiro‐inositol hexakisphosphates were recently revealed in both terrestrial and aquatic ecosystems, thus highlighting the paucity of knowledge of the origins and potential biological functions of such stereoisomers, a prevalent group of environmental organic phosphates, and their parent inositols. Some “other” inositols are medically relevant, for example, scyllo‐inositol (neurodegenerative diseases) and d ‐chiro‐inositol (diabetes). It is timely to consider exploration of the roles and applications of the “other” isomers and their derivatives, likely by exploiting techniques now well developed for the myo series.     

Quantification of myo‐inositol, 1,5‐anhydro‐ D‐sorbitol,and D‐chiro‐inositol using high‐performance liquid chromatography with electrochemical detection in very small volume clinical samples

Inositol is a six‐carbon sugar alcohol and is one of nine biologically significant isomers of hexahydroxycyclohexane. Myo‐inositol is the primary biologically active form and is present in higher concentrations in the fetus and newborn than in adults. It is currently being examined for the prevention of retinopathy of prematurity in newborn preterm infants. A robust method for quantifying myo‐inositol (MI), D ‐chiro‐inositol (DCI) and 1,5‐anhydro‐ D ‐sorbitol (ADS) in very small‐volume (25 μL) urine, blood serum and/or plasma samples was developed. Using a multiple‐column, multiple mobile phase liquid chromatographic system with electrochemical detection, the method was validated with respect to (a) selectivity, (b) accuracy/recovery, (c) precision/reproducibility, (d) sensitivity, (e) stability and (f) ruggedness. The standard curve was linear and ranged from 0.5 to 30 mg/L for each of the three analytes. Above‐mentioned performance measures were within acceptable limits described in the Food and Drug Administration's Guidance for Industry: Bioanalytical Method Validation. The method was validated using blood serum and plasma collected using four common anticoagulants, and also by quantifying the accuracy and sensitivity of MI measured in simulated urine samples recovered from preterm infant diaper systems. The method performs satisfactorily measuring the three most common inositol isomers on 25 μL clinical samples of serum, plasma, milk, and/or urine. Similar performance is seen testing larger volume samples of infant formulas and infant formula ingredients. MI, ADS and DCI may be accurately tested in urine samples collected from five different preterm infant diapers if the urine volume is greater than 2–5 mL. Copyright © 2015 John Wiley & Sons, Ltd.     

Application of a LC–MS/MS method developed for the determination of p‐phenylenediamine,N‐acetyl‐p‐phenylenediamine and N,N‐diacetyl‐p‐phenylenediamine in human urine specimens

Cases of poisoning by p‐phenylenediamine (PPD) are detected sporadically. Recently an article on the development and validation of an LC–MS/MS method for the detection of PPD and its metabolites, N‐acetyl‐p‐phenylenediamine (MAPPD) and N,N‐diacetyl‐p‐phenylenediamine (DAPPD) in blood was published. In the current study this method for detection of these compounds was validated and applied to urine samples. The analytes were extracted from urine samples with methylene chloride and ammonium hydroxide as alkaline medium. Detection was performed by LC–MS/MS using electrospray positive ionization under multiple reaction‐monitoring mode. Calibration curves were linear in the range 5–2000 ng/mL for all analytes. Intra‐ and inter‐assay imprecisions were within 1.58–9.52 and 5.43–9.45%, respectively, for PPD, MAPPD and DAPPD. Inter‐assay accuracies were within ?7.43 and 7.36 for all compounds. The lower limit of quantification was 5 ng/mL for all analytes. The method, which complies with the validation criteria, was successfully applied to the analysis of PPD, MAPPD and DAPPD in human urine samples collected from clinical and postmortem cases.     

Determination of bencycloquidium bromide in dog plasma by liquid chromatography with electrospray ionization tandem mass spectrometry

A rapid, selective and sensitive liquid chromatography/tandem mass spectrometry (LC‐MS/MS) method was developed and validated for determining bencycloquidium bromide (BCQB) in beagle dog plasma. The plasma sample was deproteinized with methanol which contained l‐ethyl‐bencycloquidium bromide as internal standard, and supernantant was assayed by LC‐MS/MS. The chromatographic separation was performed on a Phenomenex C₁₈ column (100 × 2.0 mm, i.d., 3.0 μm) with a gradient programme mobile phase consisting of methanol and ammonium acetate (5 mm) containing 0.15% acetic acid and at a flow rate of 0.3 mL/min. Electrospray ionization in positive ion mode and selective reaction monitoring was used for the quantification of BCQB with a monitored transitions m/z 330.2 → 142.1 for BCQB and m/z 344.2 → 126.2 for IS. Validation results indicated that the lower limit of quantification was 0.05 ng/mL and the assay exhibited a linear range of 0.05–10.0 ng/mL and gave a correlation coefficient of 0.9998. The intra‐ and inter‐run precisions of the assay were 1.7–4.6 and 3.2–15.6%, respectively, and the intra‐ and inter‐day accuracies were ?8.8 to 1.1 and ?5.0 to 4.6%, respectively. The developed method was applied for the pharmacokinetic study of BCQB in beagle dogs following a single intranasal dose. Copyright © 2009 John Wiley & Sons, Ltd.     

A chiral LC‐MS/MS method for the enantioselective determination of R‐(+)‐ and S‐(–)‐pantoprazole in human plasma and its application to a pharmacokinetic study of S‐(–)‐pantoprazole sodium injection

Pantoprazole, a proton pump inhibitor, is clinically used for the treatment of peptic diseases. An enantioselective LC‐MS/MS method was developed and validated for the simultaneous determination of pantoprazole enantiomers in human plasma. Pantoprazole enantiomers and the internal standard were extracted from plasma using acetonitrile. Chiral separation was carried on a Chiralpak IE column using the mobile phase consisted of 10 mm ammonium acetate solution containing 0.1% acetic acid–acetonitrile (28 : 72, v /v). MS analysis was performed on an API 4000 mass spectrometer. Multiple reactions monitoring transitions of m /z 384.1→200.1 and 390.1→206.0 were used to quantify pantoprazole enantiomers and internal standard, respectively. For each enantiomer, no apparent matrix effect was found, the calibration curve was linear over 5.00–10,000 ng/mL, the intra‐ and inter‐day precisions were below 10.0%, and the accuracy was within the range of –5.6% to 0.6%. This method was applied to the stereoselective pharmacokinetic studies in human after intravenous administration of S ‐(–)‐pantoprazole sodium injections. No chiral inversion was observed during sample storage, preparation procedure and analysis. While R ‐(+)‐pantoprazole was detected in human plasma with a slightly high concentration, which implied that S ‐(–)‐pantoprazole may convert to R ‐(+)‐pantoprazole in some subjects.     

Determination of a novel paclitaxel derivative (NPD‐103) in human plasma by ultra‐performance liquid chromatography–tandem mass spectrometry

A sensitive and specific ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC‐MS‐MS) method for quantification of a newly developed anticancer agent NPD‐103 has been established. An aliquot of human plasma sample (200 µL) was spiked with ¹³C‐labeled paclitaxel (internal standard) and extracted with 1.3 mL of tert‐butyl methyl ether. NPD‐103 was quantitated on a C₁₈ column with methanol–0.1% formic acid (75:25, v/v) as mobile phase using UPLC‐MS‐MS operating in positive electrospray ionization mode with a total run time of 3.0 min. For NPD‐103 at the concentrations of 1.0, 5.0 and 10.0 µg/mL in human plasma, the absolute extraction recoveries were 95.58, 102.43 and 97.77%, respectively. The linear quantification range of the method was 0.1–20.0 µg/mL in human plasma with linear correlation coefficients greater than 0.999. The intra‐ and inter‐day accuracy for NPD‐103 at 1.0, 5.0 and 10.0 µg/mL levels in human plasma fell into the ranges of 95.29–100.00% and 91.04–94.21%, and the intra‐ and inter‐day precisions were in the ranges of 8.96–11.79% and 7.25–10.63%, respectively. This assay is applied to determination of half‐life of NPD‐103 in human plasma. Copyright © 2008 John Wiley & Sons, Ltd.     

A liquid chromatography/tandem mass spectrometry assay for the analysis of atomoxetine in human plasma and in vitro cellular samples

A simple, rapid and sensitive method for quantification of atomoxetine by liquid chromatography–tandem mass spectrometry (LC‐MS/MS) was developed. This assay represents the first LC‐MS/MS quantification method for atomoxetine utilizing electrospray ionization. Deuterated atomoxetine (d3‐atomoxetine) was adopted as the internal standard. Direct protein precipitation was utilized for sample preparation. This method was validated for both human plasma and in vitro cellular samples. The lower limit of quantification was 3 ng/mL and 10 nm for human plasma and cellular samples, respectively. The calibration curves were linear within the ranges of 3–900 ng/mL and 10 nm to 10 µm for human plasma and cellular samples, respectively (r² > 0.999). The intra‐ and inter‐day assay accuracy and precision were evaluated using quality control samples at three different concentrations in both human plasma and cellular lysate. Sample run stability, assay selectivity, matrix effect and recovery were also successfully demonstrated. The present assay is superior to previously published LC‐MS and LC‐MS/MS methods in terms of sensitivity or the simplicity of sample preparation. This assay is applicable to the analysis of atomoxetine in both human plasma and in vitro cellular samples. Copyright © 2012 John Wiley & Sons, Ltd.     

Simultaneous quantification of antofloxacin and its major metabolite in human urine by HPLC–MS/MS,and its application to a pharmacokinetic study

This study presents a high‐performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) method for the simultaneous determination of antofloxacinin and its main metabolite – N ‐demethylated metabolite (N‐ DM) – in human urine. Ornidazole was used as the internal standard. This was a clinical urine recovery study, in which 10 healthy Chinese volunteers were intravenously administered a single 200 mg dose of antofloxacin hydrochloride. Compounds were extracted by albumen precipitation, after which samples were isocratically eluted using a Poroshell 120 SB‐C₁₈ column, and were analysed using HPLC–MS/MS under electronic spray ionization positive ion mode. The method was successfully applied in a urine pharmacokinetic study of antofloxacinin, with a detection range of 0.02/0.01 to 200/100 μg/mL (for antofioxacin/N‐ DM).The average percentages of antofioxacin/N‐ DM measured in urinary excretion frp, 10 volunteers were 54.9 ± 5.7/8.2 ± 2.5% in 120 h duration.     

Development and validation of amitriptyline and its metabolite in human plasma by ultra performance liquid chromatography-tandem mass spectrometry and its application to a bioequivalence study

A method based on ultra performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS) in combination with solid‐phase extraction for sample pretreatment has been developed for the simultaneous analysis of amitriptyline and its main metabolite in human plasma. The extraction of the analytes from plasma samples was carried out by means of a selective SPE procedure using hydrophilic–lipophilic balance cartridges. The assay involves a simple solid‐phase extraction (SPE) procedure of 0.2 mL of human plasma and analysis was performed on a triple‐quadrupole tandem mass spectrometer by multiple reactions monitoring (MRM) mode via electrospray ionization (ESI). The standard calibration curve was linear over the ranges 0.370–95.539 ng/mL for amitriptyline and 0.365–94.374 ng/mL for nortriptyline, expressed by the linear correlation coefficient r², which was better than 0.995 for both. The intra‐ and inter‐day precision and accuracy of the quality control samples were within 10.0%. The recovery was 85.3, 88.4 and 80.7% for amitriptyline, nortriptyline and doxepin respectively. Total run time was 1.2 min only for each sample, which makes it possible to analyze more than 400 samples per day. The method was highly reproducible and gave peaks with excellent chromatography properties. Copyright © 2010 John Wiley & Sons, Ltd.     

Developing a robust LC–MS/MS method to quantify Zn‐DTPA,a zinc chelate in human plasma and urine

Quantitation of Zn‐DTPA (zinc diethylenetriamene pentaacetate, a metal chelate) in complex biological matrix is extremely challenging on account of its special physiochemical properties. This study aimed to develop a robust and specific liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for determination of Zn‐DTPA in human plasma and urine. The purified samples were separated on Proteonavi (250 × 4.6 mm, 5 μm; Shiseido, Ginza, Tokyo, Japan) and a C₁₈ guard column. The mobile phase consisted of methanol–2 mm ammonium formate (pH 6.3)–ammonia solution (50:50:0.015, v/v/v), flow rate 0.45 mL/min. The linear concentration ranges of the calibration curves for Zn‐DTPA were 1–100 μg/mL in plasma and 10–2000 μg/mL in urine. The intra‐ and inter‐day precisions for quality control (QC) samples were from 1.8 to 14.6% for Zn‐DTPA and the accuracies for QC samples were from −4.8 to 8.2%. This method was fully validated and successfully applied to the quantitation of Zn‐DTPA in plasma and urine samples of a healthy male volunteer after intravenous infusion administration of Zn‐DTPA. The result showed that the concentration of Zn‐DTPA in urine was about 20 times that in plasma, and Zn‐DTPA was completely (94.7%) excreted through urine in human.     

A validated HPLC‐MS/MS method for the quantification of caderofloxacin in human plasma and its application to a clinical pharmacokinetic study

A simple, selective and rapid HPLC‐MS/MS method was developed and validated for the determination of caderofloxacin in human plasma. Sparfloxacin was used as the internal standard (IS). After precipitation with methanol and dilution with the mobile phase, the samples were injected into the HPLC‐MS/MS system. The chromatographic separation was performed on a Zorbax XDB Eclipse C₁₈ column (150 × 4.6 mm, 5 µm) with a mobile phase of ammonium acetate buffer (20 mm, pH 3.0)–methanol, 45:55 (v/v). The MS/MS analysis was done in positive mode. The multiple reaction monitoring transitions monitored were m/z 412.3 → 297.1 for caderofloxacin and m/z 393.2 → 292.2 for the IS. The calibration curve was linear over the range of 50.0–8000 ng/mL with an aliquot of 100 μL plasma. The precision of the assay was 2.0–9.4 and 6.6–11.5% for the intra‐ and inter‐run variability, respectively. The intra‐ and inter‐run accuracy (relative error) was 4.4–10.0 and ?1.2–4.0%. The total run time was 3.5 min. The assay was fully validated in accordance with the US Food and Drug Administration guidance. It was successfully applied to a pharmacokinetic study of caderofloxacin in healthy Chinese volunteers. Copyright © 2015 John Wiley & Sons, Ltd.     

A liquid chromatography-tandem mass spectrometry method for the quantitative determination of diastereomers of a phosphoramidate nucleotide prodrug (PSI-7851) in human plasma

A rapid and stereospecific method using high performance liquid chromatography–tandem mass spectrometry (HPLC‐MS/MS) for the separation and determination of PSI‐7851 diastereomers in human K₂EDTA plasma has been developed. The analytical method involves direct protein precipitation with acetonitrile, followed by separation of the diastereomers on a Luna C₁₈ column, positive mode electrospray ionization and selected reaction monitoring mode mass spectrometry detection. The mobile phase composition and pH were investigated for the resolution of the two diastereomers of PSI‐7851. The optimized method showed good resolution (R_s = 4.8) within short analysis time (approximately 8 min). The assay range was 5–2500 ng/mL for both diastereomers using a 1/x² weighted linear regression analysis for standard curve fitting. Replicate sample analysis indicated that intra‐ and inter‐day accuracy and precision were within ±15.0%. The recovery of diastereomers from human plasma was greater than 85% and no significant matrix effect was observed. The method was demonstrated to be sensitive, selective and robust, and was successfully used to support clinical studies. Copyright © 2011 John Wiley & Sons, Ltd.     

A sensitive LC‐MS/MS method for simultaneous determination of R‐bambuterol and its active metabolite R‐terbutaline in human plasma and urine with application to a clinical pharmacokinetic study

A sensitive liquid chromatography–tandem mass spectrometry (LC‐MS/MS) method for simultaneous determination of R‐bambuterol and its active metabolite R‐terbutaline in human plasma and urine was established. The inhibition for the biotransformation of R‐bambuterol in plasma was fully investigated. Plasma samples were prepared on ice and neostigmine metilsulfate added as a cholinesterase inhibitor immediately after sample collection. All samples were extracted with ethyl acetate and separated on a C₁₈ column under gradient elution with a mobile phase consisting of methanol and water containing 5 mm ammonium acetate at a flow rate of 0.6 mL/min. The analytes were detected by an API 4000 tandem mass spectrometer with positive electrospray ionization in multiple reaction monitoring mode. The established method was highly sensitive with the lower limit of quantification (LLOQ) of 10.00 pg/mL for each analyte in plasma. In urine samples, the LLOQs were 20.00 and 500.0 pg/mL for R‐bambuterol and R‐terbutaline, respectively. The intra‐ and inter‐day precisions were <12.7 and <8.6% for plasma and urine, respectively. The analytical runtime within 6.0 min per sample made this method suitable for high‐throughput determination. The validated method has been successfully applied to the human pharmacokinetic study of R‐bambuterol involving 10 healthy volunteers. Copyright © 2013 John Wiley & Sons, Ltd.     

Validated LC‐MS/MS assay for the quantitative determination of vardenafil in human plasma and its application to a pharmacokinetic study

A sensitive high‐performance liquid chromatography–tandem mass spectrometric (HPLC‐MS/MS) assay has been developed for the quantitative analysis of vardenafil in human plasma. Vardenafil and the internal standard, alprazolam, were extracted from 0.2 mL aliquots of alkalinized plasma by a single solvent extraction into hexane : dichloromethane. Reversed‐phase chromatographic separation was affected by gradient elution with mobile phases consisting of 10 mM ammonium formate pH 7.0 (solvent A) and methanol (100%, solvent B), delivered at a flow rate of 0.4 mL/min. The analytes were detected by using an electrospray ion source on a 4000 QTrap triple quadrupole mass spectrometer operating in positive ionization mode. The mass transitions were m/z 489.3 → 312.2 for vardenafil and m/z 309.2 → 281.0 for alprazolam. The assay was linear over the concentration range of 0.2–100 ng/mL, with correlation coefficients ≥0.995. The intra‐ and inter‐day precision was less than 5.4% in terms of relative standard deviation and the accuracy was within 12.7% in terms of relative error. The lower limit of quantitation was set at 0.2 ng/mL. The high sensitivity and acceptable performance of the assay allowed its application to the analysis of plasma samples obtained following the oral administration of vardenafil to healthy male volunteers in a pharmacokinetic study. Copyright © 2009 John Wiley & Sons, Ltd.     

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.     

Rapid and simultaneous determination of multiple classes of abused drugs and metabolites in human urine by a robust LC‐MS/MS method – application to urine drug testing in pain clinics

A simple LC‐MS/MS method was developed and validated for quantitatively analyzing six classes of 26 abused drugs and metabolites in human urine: (1) illicit drugs; (2) opiates; (3) synthetic opioids; (4) sedative; (5) stimulants; and (6) γ‐aminobutyric acid analogs. All urine samples were diluted with a mixture of isotope‐labeled internal standards, hydrolyzed with β‐glucuronidase and directly injected in a gradient chromatographic run. The mobile phase was composed of 0.1% formic acid in water and 0.1% of formic acid in methanol. A 4.9 min run time using the multiplexing driver and ultra‐biphenyl column (50 × 2.1 mm, 5 µm, RESTEK) allowed all drugs to have sufficient resolution in a short elute time. The overlapping liquid chromatography runs and scheduled multiple reaction monitoring acquisition method resulted in a higher overall throughput for the system. The result was linear over the studied range (2–16,000 ng/mL) for all compounds with correlation coefficients r² ≥ 0.995. The intra‐day and inter‐day precisions and accuracies were within 15% and recovery was between 83 and 115% for all analytes. Freeze–thaw stability for three cycles and long‐term stability (57 days, ?20°C) were established for all analytes. The cross‐validation between College of American Pathologists and in‐house was validated (0.06% ≤ bias ≤ 12.3%). The applicability of the method was examined by analyzing urine samples from chronic pain patients (n = 610). Copyright © 2013 John Wiley & Sons, Ltd.     

Sensitive method for the determination of paricalcitol by liquid chromatography and mass spectrometry and its application to a clinical pharmacokinetic study

A highly sensitive, specific and rapid LC‐ESI‐MS/MS method has been developed and validated for the quantification of paricalcitol (PAR) in human plasma (500 μL) using paricalcitol‐d₆ (PAR‐d₆) as an internal standard (IS) as per regulatory guidelines. A liquid–liquid extraction method was used to extract the analyte and IS from human plasma. Chromatography was achieved on Zorbax SB C₁₈ column using an isocratic mobile phase in a gradient flow. The total chromatographic run time was 6.0 min and the elution of PAR and PAR‐d₆ occurred at ~2.6 min. A linear response function was established for the range of concentrations 10–500 pg/mL in human plasma. The intra‐ and inter‐day accuracy and precision values for PAR met the acceptance criteria. The validated assay was applied to quantitate PAR concentrations in human plasma following oral administration of 4 µg capsules to humans. Copyright © 2014 John Wiley & Sons, Ltd.     

Quantification of mequitazine in human plasma by gas chromatography– quadrupole mass spectrometry and its application to a human pharmacokinetic study

A specific and sensitive gas chromatography–mass spectrometry (GC‐MS) with quadrupole mass analyzer type was developed and validated for the quantitative analysis of mequitazine in human plasma. After liquid–liquid extraction of plasma samples containing mequitazine and promethazine (internal standard, IS) using hexane with pH adjustment, the extract was evaporated and an aliquot of reconstituted residue was injected into the GC‐MS system. The assay showed linearity over a concentration range from 1 to 50 ng/mL. Intra‐ and inter‐day precision for mequitazine was <9.09 and 9.29%, respectively, and intra‐ and inter‐day accuracy ranged from ?7.97 to 9.05% and from ?1.51 to 7.89%, respectively. The lower limit of quantification was 1 ng/mL in the present assay. The developed analytical method was successfully applied to a pharmacokinetic study after a single oral administration of mequitazine in human subjects. Copyright © 2015 John Wiley & Sons, Ltd.     

Liquid chromatographic/mass spectrometry assay of bromotetrandrine in rat plasma and its application to pharmacokinetic study

A rapid and sensitive liquid chromatography–tandem mass spectrometric method (LC‐MS/MS) for the determination of bromotetrandrine in rat plasma has been developed and applied to pharmacokinetic study in Sprague–Dawley (SD) rats after a single oral administration. Sample preparation involves a liquid–liquid extraction with n‐hexane–dichlormethane (65:35, containing 1% 2‐propanol isopropyl alcohol, v/v). Bromotetrandrine and brodimoprim (internal standard, IS) were well separated by LC with a Dikma C₁₈ column using methanol–ammonium formate aqueous solution (20 mm ) containing 0.5% formic acid (60:40, v/v) as mobile phase. Detection was performed on a triple quadrupole mass spectrometer in multiple reaction monitoring mode. The ionization was optimized using ESI(+) and selectivity was achieved using MS/MS analysis, m/z 703.0 → 461.0 and m/z 339.0 → 281.0 for bromotetrandrine and IS, respectively. The present method exhibited good linearity over the concentration range of 20–5000 ng/mL for bromotetrandrine in rat plasma with a lower limit of quantification of 20 ng/mL. The intra‐ and inter‐day precisions were 2.8–7.5% and 3.2–8.1%, and the intra‐ and inter‐day accuracy ranged from ?4.8 to 8.2% and ?5.6 to 6.2%, respectively. The method was successfully applied to a pharmacokinetic study after a single oral administration to SD rats with bromotetrandrine of 50 mg/kg. Copyright © 2009 John Wiley & Sons, Ltd.     

A highly sensitive LC‐MS/MS method for the determination of S‐citalopram in rat plasma: application to a pharmacokinetic study in rats

A highly sensitive, rapid assay method has been developed and validated for the estimation of S‐citalopram (S‐CPM) in rat plasma with liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive‐ion mode. The assay procedure involves a simple liquid–liquid extraction of S‐CPM and phenacetin (internal standard, IS) from rat plasma with t‐butyl methyl ether. Chromatographic separation was operated with 0.2% formic acid:acetonitrile (20:80, v/v) at a flow rate of 0.50 mL/min on a Symmetry Shield RP₁₈ column with a total run time of 3.0 min. The MS/MS ion transitions monitored were 325.26 → 109.10 for S‐CPM and 180.10 → 110.10 for IS. Method validation and pre‐clinical sample analysis were performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 0.5 ng/mL and the linearity was observed from 0.5 to 5000 ng/mL. The intra‐ and inter‐day precisions were in the range of 1.14–5.56 and 0.25–12.3%, respectively. This novel method has been applied to a pharmacokinetic study and to estimate brain‐to‐plasma ratio of S‐CPM in rats. Copyright © 2010 John Wiley & Sons, Ltd.