Determination of olprinone in human plasma utilizing liquid chromatography tandem mass spectrometry

A sensitive and rapid method was developed for quantification of olprinone in human plasma utilizing liquid chromatography tandem mass spectrometry (LC–MS/MS). An aliquot of 1 mL plasma sample was extracted with ethyl acetate–dichloromethane. Separation of olprinone and the milrinone (internal standard, IS) from the interferences was achieved on a C₁₈ column followed by MS/MS detection. The analytes were monitored in the positive ionization mode. Multiple reaction monitoring using the transition of m/z 251 → m/z 155 and m/z 212 → m/z 140 was performed to quantify olprinone and IS, respectively. The method had a total chromatographic run time of 3 min and linear calibration curves over the concentration range of 0.5–60 ng/mL. The lower limit of quantification (LLOQ) was 0.5 ng/mL. The intra- and inter-day precisions were less than 16.3% for low QC level, and 7.1% for other QC levels, respectively. The intra- and inter-day relative errors were ranged between −12.2% and 3.7% for three QC concentration levels. The validated method was successfully applied to the quantification of olprinone concentration in human plasma after intravenous (i.v.) administration of olprinone at a constant rate of infusion of 2 μg/(kg min) for 5 min in order to evaluate the pharmacokinetics.     

Simultaneous quantification of enalapril and enalaprilat in human plasma by high-performance liquid chromatography–tandem mass spectrometry and its application in a pharmacokinetic study

A rapid, selective and sensitive high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) method was developed to simultaneously determine enalapril and enalaprilat in human plasma. With benazepril as internal standard, sample pretreatment involved in a one-step protein precipitation (PPT) with methanol of 0.2 ml plasma. Analysis was performed on an Ultimate™ XB-C₁₈ column (50 mm × 2.1 mm, i.d., 3 μm) with mobile phase consisting of methanol–water–formic acid (62:38:0.2, v/v/v). The detection was performed on a triple quadrupole tandem mass spectrometer by multiple reaction-monitoring (MRM) mode via electrospray ionization (ESI) source. Each plasma sample was chromatographed within 2.5 min. The linear calibration curves for enalapril and enalaprilat were both obtained in the concentration range of 0.638–255 ng/ml (r² ≥ 0.99) with the lower limit of quantification (LLOQ) of 0.638 ng/ml. The intra-day precision (R.S.D.) was below 7.2% and inter-day R.S.D. was less than 14%, while accuracy (relative error R.E.) was within ±8.7 and ±5.5%, determined from QC samples for enalapril and enalaprilat which corresponded to requirement of the guidance of FDA. The HPLC–MS/MS method herein described was fully validated and successfully applied to the pharmacokinetic study of enalapril maleate capsules in 20 healthy male volunteers after oral administration.     

Liquid chromatography-tandem mass spectrometry for the determination of jaceosidin in rat plasma

Jaceosidin (4′,5,7-trihydroxy–3′,6-dimethoxyflavone), isolated from Artemisia species as well as Eupatorium species, has antiallergic, anticancer, anti-inflammatory and antioxidant activity. A rapid, sensitive and selective liquid chromatography-tandem mass spectrometric (LC/MS/MS) method for the quantification of jaceosidin in rat plasma was developed to characterize the pharmacokinetics of jaceosidin. Jaceosidin and the internal standard, linezolid, were extracted from rat plasma with ethyl acetate at acidic pH and analyzed on a Luna phenyl-hexyl column using the mixture of acetonitrile and 0.1% formic acid (45:55, v/v) as a mobile phase. The analytes were determined using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The calibration curve was linear (r² = 0.9973) over the concentration range of 2.00–500 ng/ml. The lower limit of quantification for jaceosidin was 2.0 ng/ml using 50 μl of plasma sample. The coefficients of variation of intra- and inter-assay at four QC levels were 2.4–9.6% and the relative errors were −9.1 to 10.0%. The matrix effects for jaceosidin and linezolid were practically absent. The recoveries of jaceosidin and linezolid were 87.0 and 87.7%, respectively. This method was successfully applied to the pharmacokinetic study of jaceosidin in rats.     

HPLC analysis of mitoxantrone in mouse plasma and tissues: Application in a pharmacokinetic study

A simple, fast and economical HPLC assay for the determination of mitoxantrone in mouse plasma and tissue homogenates is described. Protein precipitation with sequential addition of sulfosalicylic acid and acetonitrile was used for sample preparation. The resolution of mitoxantrone and the I.S. were achieved by using acetonitrile and 10 mM sodium phosphate buffer with 0.1% TEA. The separation was performed on a Nucleosil C18, 250 mm × 4 mm I.D. column with UV detection at 610 nm. The inter-day and intra-day precision and accuracy of quality control (QC) samples, evaluated both in plasma and tissue homogenates, were all within 15%. The lower limit of quantification (LLOQ) was 5 ng/ml in plasma, 25 ng/ml in liver homogenate and 12.5 ng/ml in other tissue homogenates. This assay was successfully applied in a pharmacokinetic and tissue distribution study of mitoxantrone in mice.     

Quantitative determination of pimozide in human plasma by liquid chromatography–mass spectrometry and its application in a bioequivalence study

A simple, sensitive and specific LC–ESI/MS method was developed for the determination of pimozide in human plasma. Pimozide and cinnarizine (internal standard) were isolated from plasma samples by liquid–liquid extraction. The chromatographic separation was accomplished on a Thermo Hypersil-HyPURITY C18 reversed-phase column (150 mm × 2.1 mm, i.d., 5 μm) with the mobile phase consisting of 5 mM ammonium acetate (pH 3.5, adjusted with acetic acid)–methanol–acetonitrile (39:5:56, v/v/v). The lower limit of quantification was 0.02 ng/mL, and the assay exhibited a linear range of 0.025–12.800 ng/mL. The established method has been successfully applied to a bioequivalence study of 2 pimozide formulations in 32 healthy male Chinese volunteers.     

Quantification of artemisinin in human plasma using liquid chromatography coupled to tandem mass spectrometry

A liquid chromatographic tandem mass spectroscopy method for the quantification of artemisinin in human heparinised plasma has been developed and validated. The method uses Oasis HLB™ μ-elution solid phase extraction 96-well plates to facilitate a high throughput of 192 samples a day. Artesunate (internal standard) in a plasma–water solution was added to plasma (50 μL) before solid phase extraction. Artemisinin and its internal standard artesunate were analysed by liquid chromatography and MS/MS detection on a Hypersil Gold C18 (100 mm × 2.1 mm, 5 μm) column using a mobile phase containing acetonitrile–ammonium acetate 10 mM pH 3.5 (50:50, v/v) at a flow rate of 0.5 mL/min. The method has been validated according to published FDA guidelines and showed excellent performance. The within-day, between-day and total precisions expressed as R.S.D., were lower than 8% at all tested quality control levels including the upper and lower limit of quantification. The limit of detection was 0.257 ng/mL for artemisinin and the calibration range was 1.03–762 ng/mL using 50 μL plasma. The method was free from matrix effects as demonstrated both graphically and quantitatively.     

Rapid,sensitive and selective liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the quantification of topically applied azithromycin in rabbit conjunctiva tissues

A simple, rapid, sensitive and selective liquid chromatography–tandem mass spectrometry method was developed and validated for the quantification of azithromycin in rabbit conjunctiva tissues using roxithromycin as internal standard. Following a deproteinization procedure, the samples were eluted isocratically at a flow rate of 0.3 mL/min utilizing a mobile phase containing of 10 mM ammonium acetate (adjusted pH to 5.2 with 0.1% acetic acid)–methanol (18:82, v/v) and a SHISEIDO CAPCELL PAK C₁₈ (3.0 mm × 75 mm, 3 μm). Azithromycin and its internal standard were measured by a triple-quadrupole mass spectrometer in the selected reaction monitoring (SRM) mode with precursor-to-product qualifier transition m/z 375 [M+2H]²⁺ → 591 and m/z 837 [M+H]⁺ → 679 respectively. The method demonstrated that good linearity ranged from 10 to 2000 ng/mL with r = 0.9998. The lower limit of quantification for azithromycin in conjunctiva tissues was 10 ng/mL with good accuracy and precision. The intra- and inter-day precision (RSD) values were below 15% and accuracy (%) ranged from 90% to 110% at all QC levels. The method was applicable to ocular pharmacokinetic studies of azithromycin.     

Determination of tropisetron in human plasma by liquid chromatography–tandem mass spectrometry

A sensitive and selective liquid chromatography–tandem mass spectrometry method (LC–MS/MS) for the determination of tropisetron in human plasma was developed and validated over the concentration range of 0.100–100 ng/mL. Diphenhydramine was used as the internal standard (IS). The tropisetron and the IS were extracted from alkalized plasma samples into diethyl ether–dichloromethane (2:1, v/v) and the LC separation was performed by a Diamonsil C₁₈ column (150 mm × 4.6 mm, i.d., 5 μm). The mobile phase was methanol:water (80:20, v/v) containing 0.2% formic acid delivered at a flow rate of 0.5 mL/min. The total chromatographic run time was 4.5 min. The MS data acquisition was accomplished by selected reaction monitoring (SRM) mode with positive atmospheric pressure chemical ionization (APCI) interface. The lower limit of quantification (LLOQ) achieved was 0.100 ng/mL with precision (RSD) of 3.1% and accuracy (RE) of −0.7%. For both inter-batch and intra-batch tests, the precision (RSD) for the entire validation was less than 6.0%, and the accuracy (RE) was within the −0.5% to 0.2% range. This validated LC–MS/MS method was later used to characterize the pharmacokinetics as well as the bioequivalence of tropisetron formulations.     

Quantification of trimetazidine in human plasma by liquid chromatography-electrospray ionization mass spectrometry and its application to a bioequivalence study

A rapid, sensitive and specific liquid chromatography-electrospray ionization mass spectrometric (LC-ESI-MS) method has been developed for the quantification of trimetazidine in human plasma. The analyte and the internal standard (pseudoephedrine) were extracted from plasma samples with n-hexane-dichloromethane (1:1, v/v) and analyzed on a C18 column. The chromatographic separation was achieved within 3.5 min using the mobile phase consisting of methanol/0.05% formic acid (80:20, v/v) and the flow rate was 1.0 ml/min. Ion signals m/z 181.0 and 148.0 were measured in the positive mode for trimetazidine and pseudoephedrine, respectively. The calibration curves were linear within the range of 0.4 to approximately 120 ng/ml. The lower limit of quantification (LLOQ) was 0.4 ng/ml with 0.5 ml plasma sample. The intra- and inter-day precisions were lower than 12% in terms of relative standard deviation (RSD). The inter-day relative error (RE) as determined from quality control samples (QCs), ranged from -1.4% to 3.3%. This validated method was successfully applied to the bioequivalent evaluation of two brands of trimetazidine tablets in 20 healthy volunteers.     

A rapid HPLC method for the quantification of 3,5,4′-trimethoxy-trans-stilbene (TMS) in rat plasma and its application in pharmacokinetic study

A rapid HPLC-UV method had been developed and validated to quantify 3,5,4′-trimethoxy-trans-stilbene (TMS), a naturally occurring and pharmacologically active analog of resveratrol in rat plasma. The samples were mixed with three volumes of acetonitrile to precipitate protein. Chromatographic separation was achieved on a RP-HPLC column (Agilent ZORBAX Eclipse Plus C18: 250 mm × 4.6 mm i.d., 5 μm), which was protected by a guard column (Agilent ZORBAX Eclipse Plus C18: 12.5 mm × 4.6 mm i.d., 5 μm) through isocratic delivery of a mobile phase of acetonitrile: water (75:25, v/v) at a flow rate of 1.2 ml/min. The assay was executed at 30 °C and the UV absorbance at 320 nm was monitored. The retention time of TMS and trans-stilbene (internal standard) was 6.5 and 8.3 min, respectively. The calibration curve was linear within the range of 15–1000 ng/ml (R² > 0.998) and 15 ng/ml was the lower LOQ. The intra- and inter-day precisions were good and the RSD was all lower than 7.3%. The mean absolute recovery of TMS in plasma ranged from 99.2 to 104.1%. This HPLC method had been successfully applied to study the pharmacokinetics of TMS, which was fully dissolved with hydroxypropyl-β-cyclodextrin (HP-β-CyD). In comparison with resveratrol, TMS had greater plasma exposure, longer elimination half-life and lower clearance. As TMS had superior pharmacokinetic characteristics, its potential as a preventive or therapeutic agent in resveratrol-effective conditions or diseases should be considered.     

Development and validation of an analytical method based on high performance thin layer chromatography for the simultaneous determination of lamotrigine, zonisamide and levetiracetam in human plasma

Methods based on HPLC technology are the most frequently adopted for monitoring blood levels of novel antiepileptics. Here a rapid method based on HPTLC was developed for quantitative determination of lamotrigine (LTG), zonisamide (ZNS) and levetiracetam (LVT) in human plasma and compared with HPLC and LC-MS/MS methods. Chromatographic separation was achieved on silical gel 60F₂₅₄ plates using ethylacetate:methanol:ammonia (91:10:15 v/v/v) as mobile phase. Quantitative analysis was carried out by densitometry at a wavelength of 312, 240 and 210 nm for LTG, ZNS and LVT, respectively. Calibration curves were linear over range of 0-200 ng for LTG and ZNS and 0-400 ng for and LVT. The limit of quantification of LTG, ZNS and LTV was found to be 3.69, 3.7 and 6.85 μg/ml, respectively. Intra and inter-assay precision provided relative standard deviations lower than 10% for all three analytes. Correlation and Bland-Altman plot showed general agreement between HPTLC and LC-MS/MS quantification, with a mean bias of −0.25, −0.46 and 0.5 μg/ml for LTG ZNS and LVT, respectively. Likewise, comparison between HPLC-UV and LC-MS/MS showed good agreement for all the three compounds analyzed. In conclusion, the proposed HPTLC method is simple, rapid, precise and accurate. It therefore is appropriate for the routine quantification of therapeutic levels of LTG, ZNS and LVT in human plasma.     

An efficient HPLC method for the quantitative determination of atazanavir in human plasma suitable for bioequivalence and pharmacokinetic studies in healthy human subjects

An efficient HPLC method for the determination of atazanavir in human plasma has been developed and validated. A relatively simple mobile phase consisting of acetonitrile–ammonium formate buffer (pH 3; 10 mM) (45:55, v/v) was pumped at a low flow rate of 0.3 ml/min through a reverse phase Phenomenex^® Luna C18 (2) (5 μm, 150 mm × 2.0 mm i.d.) column maintained at 30 °C. Diazepam was used as an internal standard and the eluent was monitored at 210 nm. The major advantage of this method over previously reported procedures is that the narrow-bore HPLC column used resulted in relatively short retention times for the internal standard (6.8 min) and atazanavir (8.3 min) with excellent peak resolution and associated reduction in solvent usage. Sample preparation involved liquid–liquid extraction using 400 μl plasma treated with sodium carbonate (2 M) and extracted with a mixed organic solvent consisting of ethyl acetate–n-hexane (50:50, v/v). The organic layer was removed and evaporated to dryness under nitrogen. Samples were reconstituted in mobile phase (100 μl) and 20 μl was injected onto the column. The procedures were validated according to international standards with good reproducibility and linear response with correlation coefficients (r) consistently ≥0.999. The intra- and inter-day accuracies were 97.1 ± 5.04 and 98.0 ± 11.3 respectively at the LLOQ and between 101 ± 4.48% and 104 ± 2.09% for the QC samples. The intra- and inter-day precision were ≤11.6% RSD at the LLOQ and ≤6.78% RSD across the entire QC concentration range. Mean recovery based on high, medium and low quality control standards ranged between 94.4 ± 1.07% and 100 ± 2.22%. Plasma samples were evaluated under short-term (ambient temperature for 6 h) and long-term (−10 ± 2 °C for 2 months) storage conditions and were found to be stable. The method described is efficient and has the necessary accuracy and precision for the rapid quantitative determination of atazanavir in human plasma and is thus highly suitable for use in pharmacokinetic/bioavailability/bioequivalence studies in healthy human subjects.     

Determination of pinostrobin in rat plasma by LC-MS/MS: application to pharmacokinetics

A rapid and sensitive method for the determination of pinostrobin in rat plasma was developed using liquid chromatography tandem mass spectrometry (LC-MS/MS) for the first time. Isoliquiritigenin was used as an internal standard in rat plasma. Chromatographic separation was performed on an HiQ Sil C₁₈ column with isocratic elution at a flow rate of 1 mL/min. The mobile phase consisted of water and methanol (9:91, v/v) containing 0.1% formic acid. The quantification limit was 10 ng/mL within a linear range of 10-1000 ng/mL (R = 0.9984). The intra- and inter-day assay precision ranged from 3.8-5.3% to 3.2-5.2%, respectively, and the intra- and inter-day assay accuracy was between 93.2-95.1% and 95.5-104.3%, respectively. Our results indicated that the LC-MS/MS method is effective for pharmacokinetic study of pinostrobin in rat plasma.     

PK and tissue distribution of docetaxel in rabbits after i.v. administration of liposomal and injectable formulations

A simple and sensitive HPLC method was established and validated for the determination of docetaxel (DTX) in rabbit plasma and tissue samples. Biosamples were spiked with paclitaxel as an internal standard and pre-treated by solid phase extraction (SPE). Sample separation was performed on a reverse-phase HPLC column at 30 °C by using a mobile phase of acetonitrile–methanol–0.02 M ammonium acetate buffer (pH 5.0) (20:47.5:32.5, v/v/v) at flow rate of 1.0 mL/min The UV absorbance of the samples was measured at the wavelength of 230 nm. The standard curves were linear over the ranges of 0.02525–2.525 μg/mL for plasma, 1.010–202.00 μg/g for lung, 0.202–20.20 μg/g for spleen, liver and kidney, 0.202–10.10 μg/g for heart and stomach, 0.0505–2.02 μg/g for brain, respectively. The limits of quantification (LOQ) were 10.0 ng/mL in the plasma samples and 20.0 ng/g in the tissue samples, respectively. The analysis method was successfully applied to pharmacokinetics and tissue distribution studies of DTX liposomes and DTX injection after i.v. administration to the rabbits. The results showed that the liposome carrier led to a significant difference in pharmacokinetics and tissue distribution profile compared to the conventional DTX injection.     

Development of a high performance liquid chromatography method for quantification of PAC-1 in rat plasma

A sensitive and specific high performance liquid chromatography method with UV detection was developed and validated for the determination of PAC-1 in rat plasma. After extraction with ethyl acetate, the chromatographic separation was carried out on a Diamonsil C₁₈ column (150 mm × 4.6 mm i.d., 5 μm particle size, Zhonghuida) protected by a ODS guard column (10 mm × 4.6 mm i.d., 5 μm particle size), using acetonitrile–methanol–phosphate buffer (pH 3.0, 30 mM) (31:3:66, v/v/v) as mobile phase at a flow rate of 1.0 mL/min, and wavelength of the UV detector was set at 281 nm. No interference from any endogenous substances was observed during the elution of PAC-1 and internal standard (IS, indapamide). The calibration curve was linear over the range of 0.05–20 μg/mL (r > 0.99). The lower limit of quantification was evaluated to be 50 ng/mL. The method was successfully applied to the pharmacokinetic study of PAC-1 after intravenous and oral administration in rats, respectively.     

Determination of a peroxisome proliferator-activated receptor γ agonist, 1-(trans-methylimino-N-oxy)-6-(2-morpholinoethoxy-3-phenyl-1H-indene-2-carboxylic acid ethyl ester (KR-62980) in rat plasma by liquid chromatography–tandem mass spectrometry

A novel peroxisome proliferator-activated receptor γ (PPARγ) agonist, KR-62980, was determined by liquid–liquid extraction with ethyl acetate and liquid chromatography–tandem mass spectrometry (LC/MS/MS) in rat plasma. In order to evaluate the pharmacokinetics of KR-62980, a reliable, selective and sensitive high-performance liquid chromatographic method with electrospray ionization tandem mass spectrometry was developed for the quantification of KR-62980 in rat plasma. KR-62980 and imipramine (IS) were separated on Hypersil GOLD C18 column with a mixture of acetonitrile–ammonium formate (10 mM) (80:20, v/v) as mobile phase. The ion transitions monitored were m/z 437.2 → 114.2 for KR-62980, m/z 281.3 → 86.1 for imipramine in multiple reaction monitoring (MRM) mode. The percent recoveries of KR-62980 and imipramine were 90.1 and 98.4% from rat plasma, respectively. The linear dynamic range extended from 0.01 to 10 μg/ml with a correlation coefficient (R²) greater than 0.99 and the lower limit of quantification was 0.01 μg/ml. The mean of intra- and inter-assay precisions was 2.1 and 9.3%. The method was validated and successfully applied to the pharmacokinetic study of KR-62980 in rat.     

A direct HPLC method for the resolution and quantitation of the R-(−)- and S-(+)-enantiomers of vigabatrin (γ-vinyl-GABA) in pharmaceutical dosage forms using teicoplanin aglycone chiral stationary phase

A direct chiral high-performance liquid chromatography (HPLC) method was developed and validated for the resolution and quantification of antiepileptic drug enantiomers, R-(−)- and S-(+)-vigabatrin (gamma-vinyl-gamma-aminobutyric acid) in pharmaceutical products. The separation was optimized on a macrocyclic glycopeptide antibiotic chiral stationary phase (CSP) based on teicoplanin aglycone, chirobiotic (TAG), using a mobile phase system containing ethanol–water (80:20, v/v), at a flow rate of 0.4 ml/min and UV detection set at 210 nm. The stability of vigabatrin enantiomers under different degrees of temperature was also studied. The enantiomers of vigabatrin were separated from each other. The calibration curves were linear over a range of 100–1600 μg/ml (r = 0.999) for both enantiomers. The overall recoveries of R-(−)- and S-(+)-vigabatrin enantiomers from pharmaceutical products were in the range of 98.3–99.8% with %RSD ranged from 0.48 to 0.52%. The limit of quantification (LOQ) and limit of detection (LOD) for each enantiomer were 100 and 25 μg/ml, respectively. No interferences were found from commonly co-formulated excipients.     

Enantioselective quantification of carvedilol in human plasma by HPLC in heavily medicated heart failure patients

A simple, specific, sensitive, inexpensive and rapid HPLC method for enantioselective quantification of carvedilol in human plasma was developed in this study. S(−)- and R(+)-carvedilol and R(+)-propranolol as the internal standard were extracted from human plasma by liquid–liquid extraction using methyl tert-butyl ether. Enantioseparation was performed on a reverse-phase C18 Phenomenex Luna 5micron 150 mm × 2 mm column after chiral derivatization with 2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl isothiocyanate. The mobile phase was a mixture of water and acetonitrile. The peaks were detected using a fluorescence detector, where the excitation and emission wavelengths were set at 242 and 344 nm, respectively. The limits of quantification for the S(−)- and R(+)-carvedilol enantiomers were both 0.5 ng/ml. Combined intra- and inter-day variations for both enantiomers were less than 8.3%. The combined accuracy for both enantiomers ranged from 91.7 to 104.7%. This method was used to assay the carvedilol enantiomers in human plasma samples obtained from heavily medicated heart failure patients within the framework of a clinical trial.     

Quantitative determination of doxorubicin in the exosomes of A549/MCF-7 cancer cells and human plasma using ultra performance liquid chromatography-tandem mass spectrometry

In cancer therapy, exosomes efflux enhances resistance of cancer cells toward anticancer agents through mediating the transport of anticancer drugs outside the cells. In this study, a rapid, simple and highly sensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the determination of Doxorubicin (DOX) in exosomes of cancer cells and human plasma using Ketotifen as an internal standard (IS). Plasma samples spiked with DOX and two cancer cell lines (A549 & MCF-7) were incubated with different concentrations of DOX and IS. The analytes were then extracted with methanol after protein precipitation and the chromatographic separation was carried out using a C18 column, with a mixture of acetonitrile–water- formic acid (85:15:0.1%, v/v/v) as mobile phase. Multiple reaction monitoring (MRM) was utilized to monitor the protonated precursor to product ion transitions of m/z 544.25?>?397.16 and m/z 310.08?>?96.97 for the quantification of DOX and IS, respectively. The method was linear over ranges of 1–1000?ng/mL for DOX in plasma and 2–1000?ng/mL for DOX in exosome samples. The lower limit of quantification of this method was 1?ng/mL, 2?ng/mL and 2?ng/mL in human plasma, A549 & MCF-7 cells respectively. Intra- and inter day precision of all quality control concentrations were less than 10.33% and the accuracy values ranged from ?4.82 to 12.60%. The optimized UPLC-MS/MS method proved to be fast, specific, simple and highly sensitive and was successfully applied for the estimation of DOX in the exosomes of cancer cells and plasma.     

Determination of strychnine and brucine in rat plasma using liquid chromatography electrospray ionization mass spectrometry

A simple, sensitive and selective liquid chromatography–electrospray mass spectrometric (LC–ESI-MS) method was developed and validated for simultaneous determination of strychnine and brucine in rat plasma, using tacrine as the internal standard (IS). Sample preparation involved a liquid–liquid extraction of the analytes with n-hexane, dichloromethane and isopropanol (65:30:5, v/v/v) from 0.1 mL of plasma. Chromatographic separation was carried out on a Waters C₁₈ column using a mobile phase of methanol–20 mM ammonium formate–formic acid (32:68:0.68, v/v/v). Positive selected ion monitoring mode was used for detection of strychnine, brucine and the IS at m/z 335.2, m/z 395.2 and m/z 199.2, respectively. Linearity was obtained over the concentration range of 0.5–500 ng/mL for strychnine and 0.1–100 ng/mL for brucine. The lower limit of quantification was 0.5 ng/mL and 0.1 ng/mL for strychnine and brucine, respectively. The intra- and inter-day precision for both strychnine and brucine was less than 7.74%, and accuracy ranged from −4.38% to 2.21% at all QC levels. The method has been successfully applied to a pharmacokinetic study of processed Semen Strychni after oral administration to rats.