Simultaneous determination of evobrutinib and its metabolite evobrutinib‐diol in dog plasma by liquid chromatography combined with electrospray ionization tandem mass spectrometry

A rapid and sensitive liquid chromatography hyphenated with electrospray ionization tandem mass spectrometric method (LC–ESI–MS/MS) was developed and validated for simultaneous determination of evobrutinib and evobrutinib‐diol in dog plasma. The plasma sample was processed using acetonitrile and chromatographic separation was carried out on a Waters Acquity BEH C₁₈ column (50 × 2.1 mm, 1.7 μm). The mobile phase was composed of 0.1% formic acid and acetonitrile, with an optimized gradient elution at a flow rate of 0.4 mL/min. Detection was accomplished in selective reaction monitoring mode via electrospray ionization interface operated in positive ion mode. The precursor‐to‐product transitions for quantification were m/z 430.2 → 98.1 for evobrutinib, m/z 464.2 → 98.1 for evobrutinib‐diol and m/z 441.2 → 138.1 for ibrutinib (internal standard). The developed assay was linear over the tested concentration ranges with correlation coefficient >0.995. The LLOQ was 0.1 ng/mL for both analytes. The inter‐ and intra‐day precisions were <9.65% and the accuracy ranged from ?3.94 to 6.37%. The extraction recovery was >85.41% and no significant matrix effect was observed. The developed assay was successfully applied to the pharmacokinetic study of evobrutinib and evobrutinib‐diol in dogs after oral administration of evobrutinib at a single dose of 5 mg/kg.     

Pharmacokinetics and bioavailability study of ginsenoside Rk1 in rat by liquid chromatography/electrospray ionization tandem mass spectrometry

Ginsenoside Rk1 (Rk1) exhibited various potent biological activities. However, its pharmacokinetic profile in vivo remains unclear. In the present study, a simple and sensitive liquid chromatography tandem mass spectrometry method was developed and validated for determination of Rk1 in rat plasma and applied in a pharmacokinetic study. The sample was precipitated with acetonitrile and separated on a Zorbax Eclipse XDB C18 column (50 × 2.1 mm, 1.8 μm). The mobile phase was composed of 0.1% formic acid in water and acetonitrile at a flow rate of 0.4 mL/min. Rk1 and internal standard (ginsenoside Rg3) were quantitatively monitored with precursor‐to‐product ion transitions of m/z 765.4 → 441.5 and m/z 783.5 → 621.4, respectively. The assay was linear over the concentration range of 5–1000 ng/mL (r > 0.99) with the LLOQ of 5 ng/mL. Other parameters including intra‐ and inter‐day precision and accuracy, extraction recovery and matrix effect were within the acceptable limits. The analyte was stable under the tested storage conditions. The validated method has been successfully applied to a pharmacokinetic study of Rk1 in rat plasma after intravenous (5 mg/kg) and oral (25 mg/kg, 50 mg/kg) administration. After oral administration, Rk1 could be detected in blood at 30 min and reached the highest concentration at 4.29~4.57 h. Our results demonstrated that Rk1 showed low clearance, moderate half‐life (3.09–3.40 h) and low bioavailability (2.87–4.23%). The study will provide information for the further application of Rk1.     

Validated liquid chromatography–tandem mass spectrometry method for quantification of ticagrelor and its active metabolite in human plasma

A rapid, simple and sensitive LC–MS/MS method was established and validated for simultaneous quantification of ticagrelor and its active metabolite AR‐C124910XX in human plasma. After plasma samples were deproteinized with acetonitrile, the post‐treatment samples were chromatographed on a Dikma C₁₈ column interfaced with a triple quadrupole tandem mass spectrometer. Electrospray negative ionization mode and multiple reaction monitoring were adopted to assay ticagrelor and AR‐C124910XX. Acetonitrile and 5 mΜ ammonium acetate was used as the mobile phase with a gradient elution at a flow rate of 0.5 mL/min. The method was linear in the range of 0.781–800 ng/mL for both ticagrelor and AR‐C124910XX with a correlation coefficient ≥0.994. The intra‐ and inter‐day precisions were within 12.61% in terms of relative standard deviation and the accuracy was within ±7.88% in terms of relative error. The LC–MS/MS method was fully validated for its sensitivity, selectivity, stability, matrix effect and recovery. This convenient and specific LC–MS/MS method was successfully applied to the pharmacokinetic study of ticagrelor and AR‐C124910XX in healthy volunteers after an oral dose of 90 mg ticagrelor.     

Pharmacokinetics and excretion study of bergenin and its phase II metabolite in rats by liquid chromatography tandem mass spectrometry

A sensitive and selective liquid chromatographic–tandem mass spectrometric (LC–MS/MS) method for the determination of bergenin and its phase II metabolite in rat plasma, bile and urine has been developed. Biological samples were pretreated with protein precipitation extraction procedure and enzymatic hydrolysis method was used for converting glucuronide metabolite to its free form bergenin. Detection and quantitation were performed by MS/MS using electrospray ionization and multiple reaction monitoring. Negative electrospray ionization was employed as the ionization source. Sulfamethoxazole was used as the internal standard. The separation was performed on a reverse‐phase C₁₈ (250 × 4.6 mm, 5 μm) column with gradient elution consisting of methanol and 0.5% aqueous formic acid. The concentrations of bergenin in all biological samples were in accordance with the requirements of validation of the method. After oral administration of 12 mg/kg of the prototype drug, bergenin and its glucuronide metabolite were determined in plasma, bile and urine. Bergenin in bile was completely excreted in 24 h, and the main excreted amount of bergenin was 97.67% in the first 12 h. The drug recovery in bile within 24 h was 8.97%. In urine, the main excreted amount of bergenin was 95.69% in the first 24 h, and the drug recovery within 24 h was <22.34%. Total recovery of bergenin and its glucuronide metabolite was about 52.51% (20.31% in bile within 24 h, 32.20% in urine within 48 h). The validated method was successfully applied to pharmacokinetic and excretion studies of bergenin.     

Pharmacokinetic analysis of plasma bicyclol by liquid chromatography–tandem mass spectrometry

Bicyclol is a synthetic drug widely used to treat chronic hepatitis B. This study aimed to develop a selective, sensitive and high‐throughput liquid chromatography–tandem mass spectrometric method for the detection of bicyclol in human plasma. Bicyclol was detected using a multiple reaction monitoring mode, with ammonium adduct ions (m/z 408.2) as the precursor ion and the [M‐CH₃]⁺ ion (m/z 373.1) subjected to demethylation as the product ion. Chromatographic separation was achieved using a Zobax Eclipse XDB‐C₁₈ column with a gradient elution and a mobile phase of 2 mm ammonium formate and acetonitrile. Bicyclol was extracted from plasma matrix by precipitation. A linear detection response was obtained for bicyclol ranging from 0.500 to 240 ng/mL, and the lower limit of quantification was 0.500 ng/mL. The intra‐ and inter‐day precisions were all ≤7.4%, and the accuracies were within ±6.0%. The extraction recovery was >95.9%, and the matrix effects were between 96.0% and 108%. Bicyclol was found to be unstable in human plasma at room temperature, but the degradation was minimized by conducting sample collection and preparation in an ice bath. The validated method was successfully applied to investigate the pharmacokinetics of bicyclol tablets in six healthy Chinese volunteers.     

Simultaneous quantification of imatinib and its main metabolite N‐demethyl‐imatinib in human plasma by liquid chromatography–tandem mass spectrometry and its application to therapeutic drug monitoring in patients with gastrointestinal stromal tumor

The aim of this study was to improve and validate a more stable and less time‐consuming method based on liquid chromatography and tandem mass spectrometry (LC‐ MS/MS) for the quantitative measurement of imatinib and its metabolite N‐ demethyl‐imatinib (NDI) in human plasma. Separation of analytes was performed on a Waters XTerra RP₁₈ column (50 × 2.1 mm i.d., 3.5 μm) with a mobile phase consisting of methanol–acetonitrile–water (65:20:15, v /v/v) with 0.05% formic acid at a flow‐rate of 0.2 mL/min. The Quattro MicroTM triple quadruple mass spectrometer was operated in the multiple‐reaction‐monitoring mode via positive electrospray ionization interface using the transitions m /z 494.0 → 394.0 for imatinib, m /z 479.6 → 394.0 for NDI and m /z 488.2 → 394.0 for IS. The method was linear over 0.01–10 μg/mL for imatinib and NDI. The intra‐ and inter‐day precisions were all <15% in terms of relative standard deviation, and the accuracy was within ±15% in terms of relative error for both imatinib and NDI. The lower limit of quantification was identifiable and reproducible at 10 ng/mL. The method was sensitive, specific and less time‐consuming and it was successfully applied in gastrointestinal stromal tumor patients treated with imatinib.     

Quantification and pharmacokinetic study of entrectinib in rat plasma using ultra‐performance liquid chromatography tandem mass spectrometry

To characterize the preclinical plasma pharmacokinetics of entrectinib, a reproducible and precise assay is necessary. In this study, we developed and validated a simple ultra‐performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS) method for the measurement of entrectinib using carbamazepine as the internal standard in rat plasma. Sample preparation was a simple protein precipitation with acetonitrile, then entrectinib was eluted on an Acquity UPLC BEH C₁₈ column (2.1 × 50 mm, 1.7 μm) using a gradient elution with a mobile phase composed of acetonitrile (A) and 0.1% formic acid in water (B). Detection was achieved using multiple‐reaction monitoring in positive ion electrospray ionization mode. The method showed good linearity over the concentration range of 1–250 ng/mL (r² > 0.9951). The intra‐ and inter‐day precision was determined with the values of 6.3–12.9 and 2.6–6.9%, respectively, and accuracy values of 0.5–11.6%. Matrix effect, extraction recovery, and stability data all met the acceptance criteria of US Food and Drug Administration guidelines for bioanalytical method validation. The method was successfully applied to a pharmacokinetic study. In this study, we developed the complete validated method for the quantification of entrectinib in rat plasma.     

Simultaneous quantification of tizoxanide and tizoxanide glucuronide in mouse plasma by liquid chromatography–tandem mass spectrometry

Nitazoxanide (NTZ) is a broad‐spectrum antimicrobial agent. Tizoxanide (T) and tizoxanide glucuronide (TG) are the major circulating metabolites after oral administration of NTZ. A rapid and specific LC–MS/MS method for the simultaneous quantification of T and TG in mouse plasma was developed and validated. A simple acetonitrile‐induced protein precipitation method was employed to extract two analytes and the internal standard glipizide from 50 μL of mouse plasma. The purified samples were resolved using a C₁₈ column with a mobile phase consisting of acetonitrile and 5 mm ammonium formate buffer (containing 0.05% formic acid) following a gradient elution. An API 3000 triple quadrupole mass spectrometer was operated under multiple reaction‐monitoring mode with electrospray ionization. The precursor‐to‐product ion transitions m/z 264 → m/z 217 for T and m/z 440 → m/z 264 for TG were used for quantification. The developed method was linear in the concentration ranges of 1.0–500.0 ng/mL for T and 5.0–1000.0 ng/mL for TG. The intra‐ and inter‐day precision and accuracy of the quality control samples at low, medium and high concentrations exhibited an RSD of <13.2% and the accuracy values ranged from ?9.6 to 9.3%. We used this validated method to study the pharmacokinetics of T and TG in mice following oral administration of NTZ. Copyright © 2016 John Wiley & Sons, Ltd.     

Simultaneous determination of N‐ethylpentylone,dopamine, 5‐hydroxytryptamine and their metabolites in rat brain microdialysis by liquid chromatography tandem mass spectrometry

N‐Ethylpentylone (NEP) is a popular synthetic cathinone abused worldwide. To obtain more information about its pharmacokinetics and pharmacodynamics, a rapid, simple and sensitive liquid chromatography–tandem mass spectrometry method was developed for the determination of NEP, two important neurotransmitters, dopamine and serotonin, and their metabolites, including 3,4‐dihydroxyphenylacetic acid, 3‐methoxytyramine and 5‐hydroxyindole‐3‐acetic acid, in rat brain microdialysate. The analytes were separated on a Phnomenex Polar C₁₈ column, with a mobile phase of 0.1% formic acid in water (A) and 0.1% formic acid in acetonitrile (B) under gradient elution to shorten the total chromatographic run time. A triple quadruple mass spectrometer coupled with an electrospray ionization source in both positive and negative ion mode was used to detect the analytes. This method showed excellent accuracy (87.4–113.5%) and precision (relative standard deviation <15%) at three quality control levels. The limits of detection were 0.2 ng/mL for NEP and 0.2–50 nm for the others and good linearity was obtained. This study pioneered a method to integrate exogenous drugs and endogenous neurotransmitters as the drugs act on the same determination system, which means that this innovation can provide support for further study of the addictive effects of NEP or other synthetic cathinones on extracellular levels of dopamine and 5‐hydroxytryptamine.     

Pharmacokinetic study of dendrobine in rat plasma by ultra‐performance liquid chromatography tandem mass spectrometry

Dendrobine, considered as the major active alkaloid compound, has been used for the quality control and discrimination of Dendrobium which is documented in the Chinese Pharmacopoeia. In this work, a sensitive and simple ultra‐performance liquid chromatography tandem mass spectrometry (UPLC‐MS/MS) method for determination of dendrobine in rat plasma is developed. After addition of caulophyline as an internal standard (IS), protein precipitation by acetonitrile–methanol (9:1, v/v) was used to prepare samples. Chromatographic separation was achieved on a UPLC BEH C₁₈ (2.1 ×100 mm, 1.7 µm) column with acetonitrile and 0.1% formic acid as the mobile phase with gradient elution. An electrospray ionization source was applied and operated in positive ion mode; multiple reaction monitoring mode was used for quantification using target fragment ions m/z 264.2 → 70.0 for dendrobine and m/z 205.1 → 58.0 for IS. Calibration plots were linear throughout the range 2–1000 ng/mL for dendrobine in rat plasma. The RSDs of intra‐day and inter‐day precision were both <13%. The accuracy of the method was between 95.4 and 103.9%. The method was successfully applied to pharmacokinetic study of dendrobine after intravenous administration. Copyright © 2015 John Wiley & Sons, Ltd.     

Metabolic profiles and pharmacokinetics of goitrin in rats through liquid chromatography combined with electrospray ionization–tandem mass spectrometry

Several chemical and biological studies have revealed R,S‐goitrin as the main bioactive constituent of Isatis indigotica Fort., responsible for antiviral antiendotoxin activity; however, few pharmacokinetic studies have been conducted. To comprehend the kinetics of R,S‐goitrin and promote its curative application, a rapid and sensitive UHPLC–MS/MS method was developed. The selected reaction monitoring transitions were m/z 130.0 → 70.0 for R,S‐goitrin and m/z 181.1 → 124.0 for the internal standard in a positive‐ion mode. The established UHPLC–MS/MS method achieved good linearity for R,S‐goitrin at 10–2000 ng/mL. The intra‐ and interday accuracy levels were within ±9.7%, whereas the intraday and interday precision levels were <11.3%. The extraction recovery, stability and matrix effect were within acceptable limits. The validated method was successfully applied for the pharmacokinetic analysis of R,S‐goitrin in rats after oral administration. Moreover, a total of six metabolites were structurally identified through UHPLC–Q/TOF–MS. The proposed metabolic pathways of R,S‐goitrin in rats involve demethylation, acetylation, glutathionylation and oxygenation.     

Simultaneous determination of l‐tetrahydropalmatine and its active metabolites in rat plasma by a sensitive ultra‐high‐performance liquid chromatography with tandem mass spectrometry method and its application in a pharmacokinetic study

A sensitive and reliable ultra‐high‐performance liquid chromatography with tandem mass spectrometry (UHPLC–MS/MS) method was developed and validated for simultaneous determination of l ‐tetrahydropalmatine (l ‐THP) and its active metabolites l ‐isocorypalmine (l ‐ICP) and L ‐corydalmine (l ‐CD) in rat plasma. The analytes were extracted by liquid–liquid extraction and separated on a Bonshell ASB C₁₈ column (2.1 × 100 mm; 2.7 μm; Agela) using acetonitrile–formic acid aqueous as mobile phase at a flow rate of 0.2 mL/min in gradient mode. The method was validated over the concentration range of 4.00–2500 ng/mL for l ‐THP, 0.400–250 ng/mL for l ‐ICP and 1.00–625 ng/mL for l ‐CD. Intra‐ and inter‐day accuracy and precision were within the acceptable limits of <15% at all concentrations. Correlation coefficients (r ) for the calibration curves were >0.99 for all analytes. The quantitative method was successfully applied for simultaneous determination of l ‐THP and its active metabolites in a pharmacokinetic study after oral administration with l ‐THP at a dose of 15 mg/kg to rats.     

Enantioselective determination of ketamine in dog plasma by chiral liquid chromatography–tandem mass spectrometry

Ketamine is an N‐methyl‐d ‐aspartate receptor antagonist that is usually used clinically as a racemic mixture. Its two enantiomers exhibit different pharmacological activities. To determine whether the enantiomers have different pharmacokinetic profiles, a chiral liquid chromatography–tandem mass spectrometry method was developed and validated for the determination of ketamine enantiomers in dog plasma. The enantiomers of ketamine were extracted from 50 μL of plasma by methyl tert‐butyl ether. Adequate chromatographic retention and baseline resolution of the enantiomers were achieved within a runtime of 5 min on a chiral column coated with polysaccharide derivatives, using a gradient mobile phase of acetonitrile and 10 mm ammonium bicarbonate aqueous solution. Ketamine enantiomers were detected by mass spectrometry with multiple reaction monitoring mode using the transitions of m/z 238.3 → 125.9 for the analytes and m/z 237.1 → 194.1 for carbamazepine (internal standard). The method was linear over the concentration range from 0.5 to 500 ng/mL for each enantiomer. The lower limit of quantification (LLOQ) for each enantiomer was 0.5 ng/mL. The intra‐ and inter‐day precision was <7.3% and 8.5% for R‐ and S‐ketamine, respectively. The accuracy was 92.9–110.4% for R‐ketamine and 99.8–102.4% for S‐ketamine. The method was successfully applied to characterize the stereoselective pharmacokinetic profiles of ketamine in beagle dogs.     

Simultaneous determination of ambroxol and salbutamol in human plasma by ultra‐performance liquid chromatography–tandem mass spectrometry and its application to a pharmacokinetic study

A rapid, selective and sensitive liquid chromatography–tandem mass spectrometry assay method was developed for simultaneous determination of ambroxol and salbutamol in human plasma using citalopram hydrobromide as internal standard (IS). The sample was alkalinized with ammonia water (33:67, v/v) and extracted by single liquid–liquid extraction with ethyl acetate. Separation was achieved on Waters Acquity UPLC BEH C₁₈ column using a gradient program at a flow rate of 0.2 mL/min. Detection was performed using electrospray ionization in positive ion multiple reaction monitoring mode by monitoring the ion transitions m/z 378.9 → 263.6 (ambroxol), m/z 240.2 → 147.7 (salbutamol) and m/z 325.0 → 261.7 (IS). The total analytical run time was relatively short (3 min). Calibration curves were linear in the concentration range of 0.5–100.0 ng/mL for ambroxol and 0.2–20.0 ng/mL for salbutamol, with intra‐ and inter‐run precision (relative standard deviation) <15% and accuracy (relative error) ranging from 97.7 to 112.1% for ambroxol and from 94.5 to 104.1% for salbutamol. The method was successfully applied in a clinical pharmacokinetic study of the compound ambroxol and salbutamol tablets.     

Determination of limonin in dog plasma by liquid chromatography–tandem mass spectrometry and its application to a pharmacokinetic study

A highly sensitive liquid chromatography–tandem mass spectrometry method was developed and validated for the determination of limonin in beagle dog plasma using nimodipine as internal standard. The analyte and internal standard (IS) were extracted with ether followed by a rapid isocratic elution with 10 mm ammonium acetate buffer–methanol (26:74, v/v) on a C₁₈ column (150 × 2.1 mm i.d.) and subsequent analysis by mass spectrometry in the multiple reaction monitoring mode. The precursor to product ion transitions of m/z 469.4 → 229.3 and m/z 417.2 → 122.0 were used to measure the analyte and the IS. The assay was linear over the concentration range of 0.625–100 ng/mL for limonin in dog plasma. The lower limit of quantification was 0.312 ng/mL and the extraction recovery was >90.4% for limonin. The inter‐ and intra‐day precision of the method at three concentrations was less than 9.9%. The method was successfully applied to pharmacokinetic study of limonin in dogs. Copyright © 2012 John Wiley & Sons, Ltd.     

Evaluation of pharmacokinetics,bioavailability and urinary excretion of scopolin and its metabolite scopoletin in Sprague Dawley rats by liquid chromatography–tandem mass spectrometry

We aimed to investigate the pharmacokinetics, bioavailability and urinary excretion of scopolin and its metabolite scopoletin in rats. An LC–tandem mass spectrometry (MS/MS) method for simultaneous determination of scopolin and scopoletin in rat biomatrices was developed and validated over a plasma and urine concentration range of 5.0–2000 ng/mL. Chromatographic separation was performed on a Hypersil GOLD C₁₈ column with acetonitrile and 0.1% formic acid in water as mobile phase with gradient elution. Detection was performed in the positive ionization and selected reaction monitoring mode. The intra‐ and inter‐batch precision and accuracy, extraction recovery and matrix effect and stability of scopolin and scopoletin were well within the acceptable limits of variation. There was no gender‐related difference in the pharmacokinetic profiles of scopolin. There were significant differences in total area under the concentration–time curve (AUC), time required to achieve a maximal concentration (T_max) and apparent clearance from plasma (Cl/F) of scopoletin between the male and female rats (p < .05). The bioavailability (F) of scopolin was exceptionally low. The maximal excretion rates were 7.61 μg/h and 7.15 μg/h for scopolin and 31.68 μg/h and 25.58 μg/h for scopoletin in male and female rats, respectively. The LC–MS/MS method was successfully applied to the pharmacokinetic, bioavailability and urinary excretion studies of scopolin and its metabolite scopoletin following a single administration of scopolin to rats.     

Simultaneous quantification of oxybutynin and its active metabolite N‐desethyl oxybutynin in rat plasma by ultra‐high‐performance liquid chromatography–tandem mass spectrometry and its application in a pharmacokinetic study of oxybutynin transdermal patch

A rapid, selective and sensitive ultra‐high‐performance liquid chromatography–tandem mass spectrometry method was developed to simultaneously determine oxybutynin and its active metabolite N‐desethyl oxybutynin in rat plasma. A 0.1 mL sample of plasma was extracted with n‐hexane. Chromatographic separation was performed on a UPLC BEH C₁₈ column (2.1 × 100 mm i.d.,1.7 μm) with mobile phase of methanol–water (containing 2 mmol/L ammonium acetate and 0.1% formic acid; 90:10, v/v). The detection was performed in positive selected reaction monitoring mode. Each plasma sample was chromatographed within 3 min. The linear calibration curves were obtained in the concentration range of 0.0944–189 ng/mL (r ≥ 0.99) for oxybutynin and 0.226–18.0 ng/mL (r ≥ 0.99) for N‐desethyl oxybutynin. The intra‐ and inter‐day precision (relative standard deviation) values were not more than 14% and the accuracy (relative error) was within ±7.6%. The method described was superior to previous methods for the quantitation of oxybutynin with three product ions and was successfully applied to a pharmacokinetic study of oxybutynin and its active metabolite N‐desethyl oxybutynin in rat plasma after transdermal administration.     

Rapid quantification of lisinopril in human plasma by liquid chromatography/tandem mass spectrometry

An assay based on protein precipitation and liquid chromatography/tandem mass spectrometry (LC-MS/MS) has been developed and validated for the quantitative analysis of lisinopril in human plasma. After the addition of enalaprilat as internal standard (IS), plasma samples were prepared by one-step protein precipitation using perchloric acid followed by an isocratic elution with 10 mm ammonium acetate buffer (pH adjusted to 5.0 with acetic acid)-methanol (70:30, v/v) on a Phenomenex Luna 5 mu C(18) (2) column. Detection was performed on a triple-quadrupole mass spectrometer utilizing an electrospray ionization (ESI) interface operating in positive ion and selected reaction monitoring (SRM) mode with the precursor to product ion transitions m/z 406 --> 246 for lisinopril and m/z 349 --> 206 for enalaprilat. Calibration curves of lisinopril in human plasma were linear (r = 0.9973-0.9998) over the concentration range 2-200 ng/mL with acceptable accuracy and precision. The limit of detection and lower limit of quantification in human plasma were 1 and 2 ng/mL, respectively. The validated LC-MS/MS method has been successfully applied to a preliminary pharmacokinetic study of lisinopril in Chinese healthy male volunteers.     

Determination of azasetron hydrochloride in rabbit plasma by liquid chromatography tandem mass spectrometry and its application

A sensitive and selective liquid chromatography tandem mass spectrometry method for determination of azasetron hydrochloride in rabbit plasma was developed. After addition of doxapram hydrochloride as internal standard (IS), protein precipitation by 10% trichloroacetic acid was used as sample preparation. Chromatographic separation was achieved on a Zorbax SB-C(18) (2.1 × 50 mm, 3.5 μm) column with acetonitrile-water as mobile phase with gradient elution. An electrospray ionization source was applied and operated in positive ion mode; multiple reaction monitoring mode was used to quantification using target fragment ions m/z 349.9 → 223.5 for azasetron hydrochloride and m/z 378.9 → 291.8 for the IS. Calibration plots were linear over the range of 6-1000 ng/mL for azasetron hydrochloride in plasma. The lower limit of quantitation for azasetron hydrochloride was 6 ng/mL. The mean recovery of azasetron hydrochloride from plasma was in the range 85.6-92.7%. The RSDs of intra-day and inter-day precision were both less than 12%. This method is simple and sensitive enough to be used in pharmacokinetic research for determination of azasetron hydrochloride in rabbit plasma.     

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.