Liquid chromatography–tandem mass spectrometry method of loxoprofen in human plasma

A rapid, sensitive and selective liquid chromatography–electrospray ionization mass spectrometric method for the determination of loxoprofen in human plasma was developed. Loxoprofen and ketoprofen (internal standard) were extracted from 20 µL of human plasma sample using ethyl acetate at acidic pH and analyzed on an Atlantis dC₁₈ column with the mobile phase of methanol:water (75:25, v/v). The analytes were quantified in the selected reaction monitoring mode. The standard curve was linear over the concentration range of 0.1–20 µg/mL with a lower limit of quantification of 0.1 µg/mL. The coefficient of variation and relative error for intra‐ and inter‐assay at four quality control levels were 2.8–5.2 and 4.8–7.0%, respectively. The recoveries of loxoprofen and ketoprofen were 69.7 and 67.6%, respectively. The matrix effects for loxoprofen and ketoprofen were practically absent. This method was successfully applied to the pharmacokinetic study of loxoprofen in humans. Copyright © 2009 John Wiley & Sons, Ltd.     

Liquid chromatographic-electrospray tandem mass spectrometric determination of clarithromycin in human plasma

A rapid, sensitive and specific LC-MS-MS method has been developed for the determination of clarithromycin (CLA) in human plasma using roxithromycin (ROX) as the internal standard. Samples were prepared via liquid-liquid extraction with methyl tert-butyl ether (MTBE) and chromatographed on a Supelco RP(18) (4.6 x 50 mm, 3 microm particle size) column with a mobile phase consisting of acetonitrile:methanol:60 mM (pH 3.5) ammonium acetate buffer (32.5:32.5:35) at a constant flow rate of 0.8 mL/min. The run time was 3 min with retention times of approximately 1.65 and 1.70 min for CLA and ROX, respectively. Detection was performed on a PE Sciex API 365 mass spectrometer equipped with a turboionspray ionization source in multiple reaction monitoring (MRM) mode. The MRM pairs were m/z 748.5 --> m/z 158.2 for CLA and m/z 837.7 --> m/z 679.3 for ROX, respectively, with dwell times of 200 ms for each transition. The validated calibration curve range was 5.00-5000 ng/mL, based on 0.100 mL plasma sample volume with signal-to-noise ratio (S/N) greater than 60 for CLA at the lower limit of quantification level (5.00 ng/mL). The correlation coefficients (r(2)) of the calibration curves were better than or equal to 0.996. The inter-day (n = 18) precision and accuracy of the quality control (QC) samples were less than 3.58% RSD (relative standard deviation) and -10.8% bias, respectively. The intra-day (n = 6) precision and accuracy of the quality control samples were less than 5.0 and 12.6%, respectively. There was no significant deviation from the nominal values after a 10-fold dilution of high concentration QC samples using blank matrix. The QC samples were stable when left on the bench for 24 h or after three freeze-thaw cycles. The processed samples were also stable in HPLC autosampler at 10C for over 72 h. No matrix ionization suppression was observed when extracted blank matrix or reconstitution solvent was injected onto the system with post-column infusion of clarithromycin and roxithromycin. No carryover was observed when an extracted blank plasma sample was injected immediately after a 5000 ng/mL ULOQ (the upper limit of quantification) standard. The mean recovery was 81.5 and 78.3%, respectively, for clarithromycin and internal standard.     

Simultaneous determination of prochlorperazine and its metabolites in human plasma using isocratic liquid chromatography tandem mass spectrometry

Oral prochlorperazine (PCZ), an antiemetic, undergoes extensive first-pass metabolism. The study developed a simultaneous analytical method for PCZ and its major metabolites, prochlorperazine sulfoxide (PCZSO), N-demethylprochlorperazine (NDPCZ) and 7-hydroxyprochlorperazine (PCZOH), in human plasma using an isocratic liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. Deproteinized plasma specimens were separated using a 3 μm particle size octadecylsilyl column, and the run time was 10 min. The calibration curves were linear over the concentration ranges of 0.01-40 μg/L for PCZ, NDPCZ and PCZOH, and 0.05-80 μg/L for PCZSO. The intra- and inter-assay precisions and accuracies were within 7.0 and 99-104% and within 9.0 and 99-105%, respectively. The lower limits of quantification in human plasma were 10 ng/L for PCZ, NDPCZ and PCZOH, and 50 ng/L for PCZSO. The validated method was applied to the determination of plasma samples in 37 cancer patients receiving PCZ. Large interindividual variations were observed in plasma concentrations of PCZ, PCZSO, NDPCZ and PCZOH (relative standard deviation, 89.4, 88.7, 86.4 and 78.2%, respectively). In conclusion, this simultaneous LC-MS/MS method with acceptable analytical performance can be helpful for evaluating the pharmacokinetics of PCZ, including the determination of its metabolites in cancer patients and in clinical research.     

A sensitive and specific liquid chromatography/tandem mass spectrometry method for determination of pinaverium bromide in human plasma: application to a pharmacokinetic study in healthy volunteers

A sensitive and specific method using liquid chromatography–electrospray tandem mass spectrometry (LC‐MS/MS) for the determination of pinaverium bromide in human plasma was developed and validated. Pinaverium bromide and an internal standard (paclitaxel) were isolated from plasma samples by precipitating plasma, and determined by LC‐MS/MS in multiple‐reaction monitoring mode. The main metabolite of pinaverium bromide and endogenous substances in plasma did not show any interference. The calibration curve was linear over the plasma concentration range of 10.0–10000.0 pg/mL with a correlation coefficient of 0.9979. The relative standard derivations intra‐ and inter‐day at 30.0, 300.0 and 8000.0 pg/mL in plasma were less than 15%. The absolute recoveries of pinaverium bromide and the internal standard were 99.7–111.7 and 106.2%, respectively. The lower limit of quantitation was 10 pg/mL. The analytical method was successfully applied to study the pharmacokinetics of pinaverium bromide tablets in healthy Chinese volunteers. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of flomoxef in human plasma by liquid chromatography/electrospray ionization tandem mass spectrometry

A specific, sensitive, rapid and reproducible method for the determination of flomoxef in human plasma using high‐performance liquid chromatography–tandem mass spectrometry was developed and validated. Flomoxef was detected using an electrospay ionization method operated in negative‐ion mode. Chromatographic separation was performed in gradient elution mode on a Luna® C₁₈(2) column (3 μm , 20 × 4.0 mm) at a flow rate of 1 mL/min and runtime 3.5 min. The mobile phase consisted of acetonitrile and water containing 0.1% formic acid as additive. Extraction of flomoxef from plasma and precipitation of plasma proteins was performed with acetonitrile with an absolute recovery of 86.4 ± 1.6%. The calibration curve was linear with a correlation coefficient of 0.999 over the concentration range 10–5000 ng/mL and the lower limit of quantification was 10 ng/mL. The intra‐ and inter‐day precisions were <11.8%, while the accuracy ranged from 99.6 to 109.0%. A stability study of flomoxef revealed that it could be successfully analyzed at 4ºС over 24 h, but it was unstable in solutions at room temperature during short‐term storage (4 h) and several freeze–thaw cycles. Copyright © 2013 John Wiley & Sons, Ltd.     

Development of a liquid chromatography–isotope dilution mass spectrometry method for quantification of fentanyl in human plasma

Fentanyl is a potent analgesic drug in relieving chronic pain in patients. In this report, we present a simple, reliable and sensitive LC–ID/MS method for the quantification of fentanyl in human plasma. LC‐ID/MS analysis was carried out on a triple quadrupole mass spectrometer operated in positive electrospray ionization multiple‐reaction‐monitoring using the transitions m/z 337.6 → 187.9 for fentanyl and m/z 342.6 → 187.9 for the internal standard (D5‐fentanyl). The calibration curve covered the range 0.02–10 ng/mL. The intra‐ and inter‐batch precision were less than 6.739 and 3.126% for fentanyl and IS, with accuracy from 94.16 to 102.0%. The lower limit of quantification was identifiable and reproducible at 0.02 ng/mL. The validated method offered increased sensitivity and wide linear concentration range. This method was successfully adopted for the evaluation of bioequivalence of two fentanyl transdermal preparations after single dose administration to 20 Chinese pain‐patients. Copyright © 2009 John Wiley & Sons, Ltd.     

A liquid chromatography/tandem mass spectrometry method for determination of aristolochic acid‐I in rat plasma

A sensitive, rapid and specific liquid chromatography–electrospray ionization–tandem mass spectrometry method was developed and validated for the determination of aristolochic acid‐I (AA‐I) in rat plasma. Finasteride was used as the internal standard (IS). The analyte was separated on a Zorbax Eclipse XDB‐C₁₈ column by isocratic elution with methanol‐10 mM ammonium acetate (75:25, v/v, pH = 7.3) at a flow rate of 0.25 mL/min, and analyzed by mass spectrometry in positive multiple reaction monitoring mode. The precursor‐to‐product ion transitions of m/z 359.0 → 298.2 and m/z 373.1 → 305.2 were used to detect AA‐I and IS, respectively. Good linearity was achieved over a range of 0.4–600 ng/mL. Intra‐ and inter‐day precisions measured as relative standard deviation were less than 13.5%, and accuracy ranged from 94.2 to 97.5%. The developed method was successfully applied in the pharmacokinetic study of AA‐I in rats. Copyright © 2009 John Wiley & Sons, Ltd.     

A rapid and sensitive liquid chromatography/positive ion tandem mass spectrometry method for the determination of cimetropium in human plasma by liquid-liquid extraction

We have developed and validated a simple detection system with high-performance liquid chromatography (HPLC) with positive ion electrospray ionization tandem mass spectrometry (ESI-MS/MS) for determining cimetropium levels in human plasma using scopolamine butyl bromide as an internal standard (I.S.). The acquisition was performed in the multiple reaction monitoring (MRM) mode, by monitoring the transitions: m/z 357.9 > 103.1 for cimetropium and m/z 359.9 > 103.1 for butyl-scopolamine. The method involves a simple single-step liquid-liquid extraction with dichloromethane. The analyte was chromatographed on an YMC C18 reversed-phase chromatographic column by isocratic elution with 10 mM ammonium formate buffer-methanol (19:81, v/v; adjusted to pH 4.0 with formic acid). The results were linear over the studied range (0.2-100 ng ml(-1)), with r2 = 1.0000, and the total analysis time for each run was 2 min. Intra- and interassay precisions were 0.70-8.54% and 1.08-4.85%, respectively, and intra- and interassay accuracies were 97.56-108.23% and 97.48-103.91%, respectively. The lower limit of quantification (LLOQ) was 0.2 ng ml(-1). At this concentration, mean intra- and interassay precisions were 8.54% and 4.85%, respectively, and mean intra- and interassay accuracies were 97.56% and 98.91%, respectively. The mean recovery ranged from 62.71 +/- 4.06 to 64.23 +/- 2.32%. Cimetropium was found to be stable in plasma samples under typical storage and processing conditions. The devised assay was successfully applied to a pharmacokinetic study of cimetropium bromide administered as a single oral dose (150 mg) to healthy volunteers.     

Liquid chromatography/tandem mass spectrometry method for quantification of trans-stilbene glycoside in rat plasma and its pharmacokinetic application

A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC‐MS/MS) method was developed and validated for the quantification of trans‐stilbene glycoside (SG) in rat plasma. As trans‐SG can be rapidly isomerized under light exposure, trans‐SG plasma samples were prepared in the dark and assayed immediately. Trans‐SG and internal standard were extracted by protein precipitation. Chromatographic separation was achieved on a C₁₈ column with a gradient elution program. The detection of analytes was performed by negative ion via multiple reaction monitoring mode. The precursor‐to‐product ions of m/z 405.1 → 242.9 for trans‐SG and m/z 389.1 → 226.9 for polydatin (internal standard) were monitored. No interference of endogenous components was observed for any plasma samples that we studied.The method was linear over the concentration range of 1.0–1000.0 ng/mL with a good correlation coefficient. The lower limit of quantification was 1.0 ng/mL for trans‐SG. The intra and inter‐batch accuracy for trans‐SG in stable rat plasma samples ranged from 93.3 to 102.7% and the variation was less than 8.1%. The extraction recoveries of trans‐SG in rat plasma were from 102.8 to 112.4% and the matrix effects were also acceptable. This method was successfully applied to pharmacokinetic study of trans‐SG in rats after intravenous administration. Copyright © 2012 John Wiley & Sons, Ltd.     

Quantification of zolpidem in human plasma by liquid chromatography-electrospray ionization tandem mass spectrometry

A simple and robust method for quantification of zolpidem in human plasma has been established using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS). Es-citalopram was used as an internal standard. Zolpidem and internal standard in plasma sample were extracted using solid-phase extraction cartridges (Oasis HLB, 1 cm3/30 mg). The samples were injected into a C8 reversed-phase column and the mobile phase used was acetonitrile-ammonium acetate (pH 4.6; 10 mm) (80:20, v/v) at a flow rate of 0.7 mL/min. Using MS/MS in the selected reaction-monitoring (SRM) mode, zolpidem and Es-citalopram were detected without any interference from human plasma matrix. Zolpidem produced a protonated precursor ion ([M+H]+) at m/z 308.1 and a corresponding product ion at m/z 235.1. The internal standard produced a protonated precursor ion ([M+H]+) at m/z 325.1 and a corresponding product ion at m/z 262.1. Detection of zolpidem in human plasma by the LC-ESI MS/MS method was accurate and precise with a quantification limit of 2.5 ng/mL. The proposed method was validated in the linear range 2.5-300 ng/mL. Reproducibility, recovery and stability of the method were evaluated. The method has been successfully applied to bioequivalence studies of zolpidem.     

Liquid chromatography tandem mass spectrometry method for determination of bisoprolol in human plasma using d5‐bisoprolol as the internal standard

A simple, reliable and sensitive liquid chromatography tandem mass spectrometry (LC‐MS/MS) protocol was developed and validated for quantification of bisoprolol in human plasma. The sample was pretreated with a simple procedure of protein precipitation and an isotope‐labeled d5‐bisoprolol was used as internal standard. The chromatographic separation was performed on a Capcell Pak C₁₈ MG III column (100 mm × 2.0 mm, 5 µm). The protonated ion of the analyte was detected in positive ionization by multiple reaction monitoring mode. The mass transition pairs of m/z 326.3 → 116.3 and m/z 331.3 → 121.3 were used to detect bisoprolol and the internal standard, respectively. Linearity, accuracy, precision, recovery, matrix effect, dilution test and stability were evaluated during method validation over the range of 0.5–100 ng/mL. The validated method was successfully applied to analyze human plasma samples in a bisoprolol bioavailability study. Copyright © 2009 John Wiley & Sons, Ltd.     

Rapid and sensitive liquid chromatography tandem mass spectrometry method for the quantification of ambroxol in human plasma

A sensitive, specific and rapid high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was described and validated for the quantification of ambroxol in human plasma using enalaprilat as the internal standard (IS). Chromatographic separation was performed on a Lichrospher CN column with a mobile phase of methanol and water (containing 0.1% formic acid) (70:30, v/v). The total run time was 5.0 min for each sample. The analytes was detected by mass spectrometry with electrospray ionization source in positive selected reaction monitoring mode. The precursor-fragment ion reaction for ambroxol was m/z 378.9 --> 263.8, and for IS was m/z 349.0 --> 205.9. The linearity was established over the concentration range of 1.56-400.00 ng/mL. The inter-day and the intra-day precisions were all within 10%. A simple protein precipitation with methanol was adopted for sample preparation. The extraction recoveries of ambroxol and IS were higher than 90.80%. The validated method was successfully applied in pharmacokinetic study after oral administration of 90 mg ambroxol to 24 healthy volunteers.     

Rapid and sensitive liquid chromatography-tandem mass spectrometry method for the estimation of nicorandil in human plasma

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the estimation of nicorandil in human plasma. Nicorandil was extracted from human plasma using solid-phase extraction technique. Imipramine was used as the internal standard. A Betasil C18 column provided chromatographic separation of analytes followed by detection with mass spectrometry. The method involves a rapid solid-phase extraction from plasma, simple isocratic chromatography conditions and mass spectrometric detection that enables detection at nanogram levels. The proposed method has been validated for a linear range of 1.0-500.0 ng/mL with a correlation coefficient of > or =0.9993. The intra-run and inter-run precision and accuracy was within 10.0%. The overall recovery for nicorandil was 63.81%. The total run time was just 3.0 min.     

Reliable and sensitive determination of dutasteride in human plasma by liquid chromatography–tandem mass spectrometry

An accurate and precise method was developed and validated using LC‐MS/MS to quantify dutasteride in human plasma. The analyte and dutasteride‐13C6 as internal standard (IS) were extracted from 300 μL plasma volume using methyl tert‐butyl ether–n‐hexane (80:20, v/v). Chromatographic analysis was performed on a Gemini C₁₈ (150 × 4.6 mm, 5 µm) column using acetonitrile–5 mm ammonium formate, pH adjusted to 4.0 with formic acid (85:15, v/v) as the mobile phase. Tandem mass spectrometry in positive ionization mode was used to quantify dutasteride by multiple reaction monitoring. The entire data processing was done using Watson LIMS^TM software, which provided excellent data integrity and high throughput with improved operational efficiency. The calibration curve was linear in the range of 0.1–25 ng/mL, with intra‐and inter‐batch values for accuracy and precision (coefficient of variation) ranging from 95.8 to 104.0 and from 0.7 to 5.3%, respectively. The mean overall recovery across quality controls was ≥95% for the analyte and IS, while the interference of matrix expressed as IS‐normalized matrix factors ranged from 1.01 to 1.02. The method was successfully applied to support a bioequivalence study of 0.5 mg dutasteride capsules in 24 healthy subjects. Assay reproducibility was demonstrated by reanalysis of 103 incurred samples. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Liquid chromatography–tandem mass spectrometry method for simultaneous quantification of urapidil and aripiprazole in human plasma and its application to human pharmacokinetic study

A sensitive and selective liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed and validated for simultaneous determination of urapidil and aripiprazole in human plasma. A simple liquid–liquid extraction with ethyl acetate was used for the sample preparation. Chromatographic separation was achieved on a Phenomenex C₁₈ (4.6 × 50 mm, 5 µm) column with 0.1% formic acid–acetonitrile (10:90, v/v) as the mobile phase with flow rate of 0.6 mL/min. The quantitation of the target compounds was determined in a positive ion multiple reaction monitoring mode. Calibration plots were linear over the range of 2.0–2503.95 ng/mL for urapidil and 1.0–500.19 ng/mL for aripiprazole. The lower limit of quantitation for urapidil and aripiprazole was 2.0 and 1.0 ng/mL, respectively. Mean recovery was in the range of 69.94–75.62% for both analytes and internal standards. Intra‐day and inter‐day precisions of the assay at three concentrations were 2.56–5.89% with accuracy of 92.31–97.83% for urapidil, and 3.14–6.84% with accuracy of 91.38–94.42% for aripiprazole. The method was successfully applied to human pharmacokinetic study of urapidil and aripiprazole in healthy human male volunteers. Copyright © 2013 John Wiley & Sons, Ltd.     

Sensitive and rapid simultaneous quantitation of leucovorin and its major active metabolite 5-methyl-tetrahydrofolate in human plasma using a liquid chromatography coupled with triple quadruple mass spectrometry

Bioanalysis of an endogenous compound such as leucovorin is never an easy task on a liquid chromatography tandem mass spectrometer (LC–MSMS). Unless it is necessary, regulatory guidance discourages working with surrogate matrices for calibration curve standard preparation. Herein, a selective and sensitive liquid chromatography–tandem mass spectrometry method for simultaneous determination of leucovorin and 5-methyl tetrahydrofolic acid in human plasma was developed and validated. Stable labeled internal standards, i.e. leucovorin D₄ and 5- methyl tetrahydrofolic acid ¹³C₅, were used as internal standards to track and compensate the parent compounds during processing and extraction from plasma. The method involves a rapid solid-phase extraction from plasma followed by reverse-phase gradient chromatography and mass spectrometry detection with a total run time of 5 min. The method was developed and validated from 5 to 2,202 ng/ml for leucovorin and from 5 to 1,300 ng/ml for 5-methyl tetrahydrofolic acid. The mean recoveries for leucovorin and 5-methyl tetrahydrofolic acid were 100.4 and 100.9% respectively. The validated method enabled the simultaneous analysis of leucovorin and 5-methyl tetrahydrofolic acid in samples from clinical pharmacokinetic studies of leucovorin. The peak concentrations of leucovorin and 5-methyl tetrahydrofolic acid were 651–883 and 518–635 ng/ml, respectively, in fasted and fed conditions. The terminal half-life values for leucovorin and 5-methyl tetrahydrofolic acid were 9.3–10.5 and 9.2–17.6 h, respectively.     

Simultaneous determination of midazolam and 1'-hydroxymidazolam in human plasma by liquid chromatography with tandem mass spectrometry

A sensitive and simple liquid chromatography-tandem mass spectrometry method for the determination of midazolam and 1'-hydroxymidazolam in human plasma has been developed and validated with a dynamic range of 0.1-250 ng/mL. The analysis was based on semi-automated liquid-liquid extraction followed by evaporation of the extraction solvent, reconstitution and chromatography on a reversed-phase C(18) column. The mobile phase consists of 5 mm ammonium acetate and methanol and runs in gradient at a flow rate of 0.25 mL/min with column temperature of approximately 20 degrees C. The entire column effluent was transferred into the LC-MS/MS interface operated in positive electrospray ionization mode. The chromatographic run time was 4.3 min per injection, with retention times for midazolam, 1'-hydroxymidazolaml and the internal standard, triazolam, of 2.5, 2.3 and 2.1 min, respectively. The intra-day and inter-day precision (RSD %) and accuracy (bias %) of the quality control samples were <15.0% and within +/-13%, respectively. The current method has been applied to a clinical drug-drug interaction study in human.     

Sensitive and selective liquid chromatography–tandem mass spectrometry method for the determination of metoclopramide in human plasma: application to a bioequivalence study

A simple, sensitive and rapid method has been developed and validated for determination of the metoclopramide (MCP) in 100 μL human plasma. The analytical procedure involves a liquid–liquid extraction method using tramadol as an internal standard (IS). Chromatographic separation was carried out on a HyPURITY ADVANCE column using a mobile phase consisting of acetonitrile and 10 mm ammonium acetate buffer in the ratio of 80:20 (v/v) at a flow rate of 0.3 mL/min. The total run time of analysis was 2.5 min and elution of MCP and IS occurred at 0.9 and 1.3 min, respectively. A linear response function was established for the range of concentrations 0.53–42.07 ng/mL (r > 0.99). The intra‐ and inter‐day precision values for MCP met the acceptance as per FDA guidelines. MCP was stable in a battery of stability studies viz., bench‐top, auto‐sampler and freeze–thaw cycles. The developed assay method was successfully applied to an oral bioequivalence study in humans. Copyright © 2010 John Wiley & Sons, Ltd.     

Highly sensitive method for the determination of omeprazole in human plasma by liquid chromatography-electrospray ionization tandem mass spectrometry: application to a clinical pharmacokinetic study

A highly sensitive, rapid assay method has been developed and validated for the estimation of omeprazole (OPZ) in human plasma with liquid chromatography coupled to tandem mass spectrometry with electrospray ionization in the positive-ion mode. The assay procedure involves alkalinization of plasma followed by simple liquid-liquid extraction of OPZ and lansoprazole (internal standard, IS) from human plasma with acetonitrile. Chromatographic separation was achieved with 0.01 M ammonium acetate:acetonitrile (40:60, v/v) at a flow rate of 0.25 mL/min on an Inertsil ODS 3 column with a total run time 2.5 min. The MS/MS ion transitions monitored were 346.1 --> 198.1 for OPZ and 370.1 --> 252.1 for IS. Method validation and clinical sample analysis were performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 0.05 ng/mL and the linearity was observed from 0.05 to 10.0 ng/mL. The intra-day and inter-day precisions were in the ranges 2.09-8.56 and 5.29-8.19%, respectively. This novel method has been applied to a pharmacokinetic study of OPZ in humans.