Simultaneous stereoselective analysis of venlafaxine and O-desmethylvenlafaxine enantiomers in human plasma by HPLC-ESI/MS using a vancomycin chiral column

A high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI/MS) method for simultaneous stereoselective analysis of venlafaxine (VEN) and its major metabolite O-desmethylvenlafaxine (ODV) enantiomers in human plasma has been developed and validated. Chiral chromatography is performed on the CHRIOBIOTIC V (5 microm, 250 mm x 4.6 mm) column with mobile phase constituted of 30 mmol/l ammonium acetate-methanol (15:85, pH 6.0) at a flow rate of 1.0 ml/min and a postcolumn splitting ratio of 3:1. The compounds were ionized in the electrospray ionization (ESI) ion source of the mass spectrometer and detected using the selected ion recording (SIR) mode. Calibration curves obtained from spiked plasma were linear in the range of 5.0-400 ng/ml for S-(+)-VEN and R-(-)-VEN, 4.0-280 ng/ml for S-(+)-ODV and R-(-)-ODV, respectively, with linear correlation coefficient all above 0.999. The average extraction recoveries for all the four analytes were above 76%. The methodology recoveries were higher than 92%. The limit of detection were 1.0 ng/ml for S-(+)-VEN and R-(-)-VEN, 1.5 ng/ml for S-(+)-ODV and R-(-)-ODV, respectively. The intra- and inter-day variation coefficients were less than 9%.     

Liquid chromatography-tandem mass spectrometry (LC-MS-MS) method for simultaneous determination of venlafaxine and its active metabolite O-desmethyl venlafaxine in human plasma

A rapid and sensitive liquid chromatography-tandem mass spectrometry (LC-MS-MS) method has been developed and validated for simultaneous quantification of venlafaxine (VEN) and O-desmethyl venlafaxine (ODV) in human plasma. The analytes were extracted from human plasma by using solid-phase extraction (SPE) technique. Escitalopram (ESC) was used as the internal standard. A Betasil C18 column provided chromatographic separation of analytes followed by detection with mass spectrometry. The mass transition ion-pair has been followed as m/z 278.27-->121.11 for VEN, m/z 264.28-->107.10 for ODV and m/z 325.00-->262.00 for ESC. The method involves a 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 with linear range of 3-300 ng/ml for VEN and 6-600 ng/ml for ODV. The intrarun and interrun precision and accuracy values are within 10%. The overall recoveries for VEN and ODV were 95.9 and 81.7%, respectively. Total elution time as low as 3 min only.     

Simultaneous determination of clozapine, olanzapine, risperidone and quetiapine in plasma by high-performance liquid chromatography-electrospray ionization mass spectrometry

Clozapine (CLZ), olanzapine (OLZ), risperidone (RIP) and quetiapine (QTP) have been widely used in the treatment of schizophrenia. However, no study (or little study) has been conducted to determine the four drugs simultaneously by the use of high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-MS/ESI). OBJECTIVE: To develop a sensitive method for simultaneous determination of CLZ, OLZ, RIP and QTP in human plasma by HPLC-MS/ESI. METHODS: The analytes were extracted twice by ether after samples had been alkalinized. The HPLC separation of the analytes was performed on a MACHEREY-NAGEL C(18) ( [Formula: see text] mm, 3 microm, Germany) column, using water (formic acid: 2.70 mmol/l, ammonium acetate: 10 mmol/l)-acetonitrile (53:47) as mobile phase, with a flow-rate of 0.16 ml/min. The compounds were ionized in the electrospray ionization (ESI) ion source of the mass spectrometer and were detected in the selected ion recording (SIR) mode. RESULTS: The calibration curves were linear in the ranges of 20-1000 ng/ml for CLZ and QTP, 1-50 ng/ml for OLZ and RIP, respectively. The average extraction recoveries for all the four analysts were at least above 80%. The methodology recoveries were higher than 91% for the analysts. The intra- and inter-day R.S.D. were less than 15%. CONCLUSION: The method is accurate, sensitive and simple for routine therapeutic drug monitoring (TDM) and for the study of the pharmacokinetics of the four drugs.     

Simultaneous quantification of venlafaxine and O-desmethylvenlafaxine in human plasma by ultra performance liquid chromatography–tandem mass spectrometry and its application in a pharmacokinetic study

A rapid, selective and sensitive ultra performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) method was developed to simultaneously determine venlafaxine (VEN) and O-desmethylvenlafaxine (ODV) in human plasma. Sample pretreatment involved a one-step extraction with diethyl ether of 0.5 mL plasma. The separation was carried out on an ACQUITY UPLC? BEH C₁₈ column with 10 mmol/L ammonium acetate and methanol as the mobile phase at a flow rate of 0.30 mL/min. The detection was performed on a triple–quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) mode via electrospray ionization (ESI) source. The linear calibration curves for VEN and ODV were both obtained in the concentration range of 0.200–200 ng/mL (r² ≥ 0.99) with the lower limit of quantification (LLOQ) of 0.200 ng/mL. The intra- and inter-day precision (relative standard deviation, R.S.D.) values were less than 13% and the accuracy (relative error, R.E.) was within ±5.3% and ±3.6% for VEN and ODV. The method herein described was superior to previous methods in sensitivity and sample throughput and successfully applied to clinical pharmacokinetic study of venlafaxine sustained-release capsule in healthy male volunteers after oral administration.     

Application of high-performance liquid chromatography-mass spectrometry to detection of diuretics in human urine

A rapid, sensitive and reliable high-performance liquid chromatographic-mass spectrometric method for the detection of 25 diuretics in human urine has been developed. Atmosphere pressure chemical ionization (APCI) and electrospray ionization (ESI) modes were evaluated. A 2-ml volume of urine was extracted under basic conditions and separated on an Agilent Zorbax SB-C(18) column (150 x 2.1 mm, 5 microm). The mobile phase consisted of formic ammonium-formic acid buffer (pH 3.5) and acetonitrile. The effects of capillary temperature, sheath gas pressure and compositions of mobile phase on the sensitivity were studied. The recoveries of most of the diuretics were 75-95%. In the full scan mode, the limits of detection of the 25 diuretics were 0.25-25 ng/ml for APCI and 0.6-250 ng/ml for ESI. Under the optimal conditions, 14 diuretics from authentic urine samples were detected successfully by LC-APCI-MS. To obtain more fragmentation information on the chemical structure for positive confirmation, tandem mass analysis was also investigated.     

Determination of lonazolac and its hydroxy and O-sulfated metabolites by on-line sample preparation liquid chromatography with fluorescence detection

A reliable method, which can be used for the determination of lonazolac and its hydroxylated and O-sulfated metabolites in cell culture media with methyllonazolac as the internal standard is described. The procedure employs on-line sample enrichment using a BioTrap 500 MS (20 x 4 mm I.D.) extraction pre-column and subsequent gradient separation on an Xterra MS C18-HT (100 x 3 mm I.D., 3.5 microm particles) analytical column in the back-flush mode. Signal monitoring was done by measurement of fluorescence responses at 273 nm for excitation and 385 nm for emission. Structural identity of analyte peaks was confirmed by liquid chromatography coupled to mass spectroscopy (LC-MS-MS) using an electrospray ionization (ESI) source in the selected reaction monitoring (SRM) mode. Mean recoveries of lonazolac, hydroxylonazolac and lonazolac sulfate, respectively, from the biological matrix were 104.2 +/- 3.5, 96.7 +/- 2.2, and 100.9 +/- 3.5%. The limit of detection (LOD) for the three compounds was about 5 ng/ml using a total sample volume of only 50 microl. Linearity of signal responses versus concentration for all three analytes was accomplished in the range 10-600 ng/ml. The mean values of the coefficients of variation (CV) for quality control samples measured in duplicate at three different days at the 10, 40, 100, and 400 ng/ml level were 4.46 +/- 1.15, 3.94 +/- 2.13 and 4.79 +/- 2.07% for lonazolac, hydroxylonazolac and lonazolac sulfate. The target analytes were sufficiently stable at both storage and sample preparation conditions because no substantial deviations between analyte concentrations measured before and after subsequently performed freeze and thaw cycles were observed.     

Development and validation of liquid chromatography-tandem mass spectrometric method for simultaneous determination of fosinopril and its active metabolite fosinoprilat in human plasma

A highly sensitive and selective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for simultaneous determination of the prodrug fosinopril and its major active metabolite fosinoprilat for pharmacokinetic studies in healthy subjects. In order to get the lower limit of quantification (LLOQ), especially for analysis of fosinopril, key points of the method have been investigated including chromatographic conditions and selection of LC-MS/MS conditions. The analytes were extracted from plasma samples by liquid-liquid extraction, separated on a reversed-phase C(8) column using gradient procedure, and detected by tandem mass spectrometry with a triple quadrupole ionization interface. The analytes and internal standard zaleplon were detected using positive electrospray ionization (ESI) in the SRM mode. The LLOQ of the method down to 0.1 ng mL(-1) for fosinopril and 1.0 ng mL(-1) for fosinoprilat were identifiable and reproducible. The standard calibration curves for both fosinopril and fosinoprilat were linear over the ranges of 0.1-15.0 and 1.0-700 ng mL(-1) in human plasma, respectively. The within- and between-batch precisions (relative standard deviation (RSD)%) and the accuracy were acceptable. The validated method was successfully applied to reveal the pharmacokinetic properties of fosinopril and fosinoprilat after oral administration.     

Determination of 17 illicit drugs in oral fluid using isotope dilution ultra-high performance liquid chromatography/tandem mass spectrometry with three atmospheric pressure ionizations

The collection of oral fluid for drug testing is easy and non-invasive. This study developed a drug testing method using ultra-high performance liquid chromatography/tandem mass spectrometry (UHPLC-MS/MS) in selected-reaction monitoring (SRM) mode. We tested the method on the analysis of four opiates and their metabolites, five amphetamines, flunitrazepam and its two metabolites, and cocaine and its four metabolites in oral fluid. 100-μL samples of oral fluid were diluted with twice the amount of water then spiked with isotope-labeled internal standards. After the samples had undergone high-speed centrifugation for 20 min, we analyzed the supernatant. The recovery of the sample preparation ranged from 81 to 108%. We compared the performance of electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI). The ion suppression of most analytes on ESI (28-78%) was lower than that of APCI and APPI. A post-column flow split (5:1) did not reduce the matrix effect on ESI. Direct APPI performed better than dopant-assisted APPI using toluene. ESI, APCI and APPI limits of quantitation mostly ranged from 0.11 to 1.9 ng/mL, 0.02 to 2.2 ng/mL and 0.02 to 2.1 ng/mL, respectively, but were much higher on amphetamine and ecgonine methyl ester (about 2.7-4.7 ng/mL, 8.7-14 ng/mL, and 10-19 ng/mL, respectively). Most of the bias percentages (accuracy) and relative standard deviations (precision) on spiked samples were below 15%. This method greatly simplifies the process of sample preparation and shortens the chromatographic time to only 7.5 min per run and is able to detect analytes at sub-ppb levels.     

Feasibility of an on-line restricted access material/liquid chromatography/tandem mass spectrometry method in the rapid and sensitive determination of organophosphorus triesters in human blood plasma

A rapid on-line solid phase extraction/liquid chromatography/tandem mass spectrometry (SPE/LC/MS/MS) method using restricted access material (RAM) was developed for the simultaneous determination of eight organophosphorus triesters in untreated human blood plasma. In a process involving column-switching techniques, the analytes were enriched on the RAM column, separated using a C-18 analytical column and detected with LC/MS. Tandem mass spectrometry was used to characterize and quantify the analytes. To elucidate the fragmentation pathway of a number of the analytes, MS3 experiments using an ion trap mass spectrometer were performed. The matrix effects associated with using APCI and ESI interfaces were investigated. The recoveries obtained were in the range 60-92% (R.S.D.<6%), with estimated detection limits between 0.2 and 1.8 ng/ml of plasma, and the total analysis time was 27 min.     

Simultaneous determination of selegiline-N-oxide,a new indicator for selegiline administration,and other metabolites in urine by high-performance liquid chromatography–electrospray ionization mass spectrometry

In order to discriminate selegiline (SG) use from methamphetamine (MA) use, the urinary metabolites of SG users have been investigated using high-performance liquid chromatography (HPLC)–electrospray ionization mass spectrometry (HPLC–ESI–MS). Selegiline-N-oxide (SGO), a specific metabolite of SG, was for the first time detected in the urine, in addition to other metabolites MA, amphetamine (AP) and desmethylselegiline (DM-SG). A combination of a Sep-pak C₁₈ cartridge for the solid-phase extraction, a semi-micro SCX column (1.5 mm I.D.×150 mm) for HPLC separation and ESI–MS for detection provided a simple and sensitive procedure for the simultaneous determination of these analytes. Acetonitrile–10 mM ammonium formate buffer adjusted to pH 3.0 (70:30, v/v) at a flow-rate of 0.1 ml/min was found to be the most effective mobile phase. Linear calibration curves were obtained over the concentration range from 0.5 to 100 ng/ml for all the analytes by monitoring each protonated molecular ion in the selected ion monitoring (SIM) mode. The detection limits ranged from 0.1 to 0.5 ng/ml. Upon applying the scan mode, 10–20 ng/ml were the detection limits. Quantitative investigation utilizing this revealed that SGO was about three times more abundant (47 ng/ml, 79 ng/ml) than DM-SG in two SG users’ urine samples tested here. This newly-detected, specific metabolite SGO was found to be an effective indicator for SG administration.     

Development and validation of a liquid chromatography-tandem mass spectrometric assay for pitavastatin and its lactone in human plasma and urine

A rapid, selective and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method with electrospray ionization (ESI) was developed and validated for the simultaneous determination of pitavastatin and its lactone in human plasma and urine. Following a liquid-liquid extraction, both the analytes and internal standard racemic i-prolact were separated on a BDS Hypersil C(8) column, using methanol-0.2% acetic acid in water (70: 30, v/v) as the mobile phase. The mass spectrometer was operated in multiple reaction monitoring (MRM) mode using the transition m/z 422.4-->m/z 290.3 for pitavastatin, m/z 404.3-->m/z 290.3 for pitavastatin lactone and m/z 406.3-->m/z 318.3 for the internal standard, respectively. Linear calibration curves of pitavastatin and its lactone were obtained in the concentration range of 1-200 ng/ml, with a lower limit of quantitation of 1 ng/ml. The intra- and inter-day precision values were less than 4.2%, and accuracies were between -8.1 and 3.5% for both analytes. The proposed method was utilized to support clinical pharmacokinetic studies of pitavastatin in healthy subjects following oral administration.     

A sensitive and selective HPLC/ESI-MS/MS assay for the simultaneous quantification of 16-dehydropregnenolone and its major metabolites in rabbit plasma

A sensitive, selective and rapid liquid chromatographic/electrospray ionization tandem mass spectrometric assay was developed and validated for the simultaneous quantification of 16-dehydropregnenolone (DHP) and its five metabolites 4,16-pregnadien-3, 20-dione (M(1)), 5-pregnene-3beta-ol-20-one (M(2)), 5-pregnene-3beta, 20-diol (M(3)), 5-pregnene-3beta-ol-16, 17-epoxi-20-one (M(4)) and 5,16-pregnadien-3beta, 11-diol-20-one (M(5)) in rabbit plasma using dexamethasone as internal standard (IS). The analytes were chromatographed on Spheri-5 RP-18 column (5 microm, 100 mm x 4.6 mm i.d.) coupled with guard column using acetonitrile:ammonium acetate buffer (90:10, v/v) as mobile phase at a flow rate of 0.65 ml/min. The quantitation of the analytes was carried out using API 4000 LC-MS-MS system in the multiple reaction monitoring (MRM) mode. The method was validated in terms of linearity, specificity, sensitivity, recovery, accuracy, precision (intra- and inter-assay variation), freeze-thaw, long-term, auto injector and dry residue stability. Linearity in plasma was observed over a concentration range of 1.56-400 ng/ml with a limit of detection (LOD) of 0.78 ng/ml for all analytes except M(3) and M(5) where linearity was over the 3.13-400 ng/ml with LOD of 1.56 ng/ml. The absolute recoveries from plasma were consistent and reproducible over the linearity range for all analytes. The intra- and inter-day accuracy and precision method were within the acceptable limits and the analytes were stable after three freeze-thaw cycles and their dry residues were stable at -60 degrees C for 15 days. The method was successfully applied to determine concentrations of DHP and its putative metabolites in plasma during a pilot pharmacokinetic study in rabbits.     

Determination of urinary phytoestrogens by HPLC-MS/MS: a comparison of atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI)

A comparison of the analytical performance of atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI) for the quantitative determination of six urinary phytoestrogens (daidzein, O-desmethylangolensin, equol, enterodiol, enterolactone and genistein) by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) is presented here. Both APCI and ESI were suitable for the analysis of these compounds; however, ESI did improve measurement imprecision and sensitivity in certain cases. Method imprecision (between-run coefficients of variation [CVs] from duplicate analysis of three quality control [QC] urine pools across 20 runs) was 5.6-12% for ESI, as opposed to 5.3-30% for APCI. At low concentrations (3-60 ng/mL, analyte dependent) imprecision was lower with ESI, whereas both techniques were generally commensurate at high concentrations (200-1000 ng/mL, analyte dependent). Method accuracy (spiked analyte recovery from the QC pools) was comparable between techniques: 86-114% for ESI; 95-105% for APCI. Limits of detection (LODs) were equivalent or better with ESI compared to APCI, with the most significant LOD improvement observed for equol (ESI: 0.3 ng/mL; APCI: 2.7 ng/mL). This translated into a substantial increase in equol detection frequency (% of sample results above LOD) within a random patient sample subset (98% for ESI, compared to 81% for APCI, n=378). Correlation (Pearson) and agreement (Deming regression, Bland-Altman bias) between ESI and APCI results in the patient subset was better in cases where imprecision and sensitivity was similar for both techniques (daidzein, enterolactone, genistein: r=0.993-0.998; slope=0.98-1.03; bias=-4.2 to -0.8%); correlation and/or agreement was poorer for analytes, where APCI imprecision and sensitivity were inferior (equol, O-desmethylangolensin, enterodiol). Baring significant factors arising from differences in ionization source design, these observations suggest that ESI is more appropriate for urinary biomonitoring of these compounds by LC-MS/MS.     

Simultaneous measurement of venlafaxine and its major metabolite, oxydesmethylvenlafaxine, in human plasma by high-performance liquid chromatography with coulometric detection and utilisation of solid-phase extraction

Venlafaxine, oxydesmethylvenlafaxine and an internal standard (paroxetine) were extracted from plasma by a solid-phase extraction technique. Chromatography was performed using isocratic reversed-phase high-performance liquid chromatography (HPLC) with coulometric endpoint detection. The standard curves were linear over the range 0–200 ng/ml for both venlafaxine and oxydesmethylvenlafaxine in plasma. The mean inter- and intra-assay coefficients of variation over the range of the standard curves were less than 10%. The absolute recovery averaged 74% for venlafaxine and 67% for oxydesmethylvenlafaxine. The sensitivity was 0.5 ng for both the analytes. Plasma profiles of the analytes following oral administration of venlafaxine, are presented.     

Determination of metolazone in human blood by liquid chromatography with electrospray ionization tandem mass spectrometry

A rapid, sensitive and accurate liquid chromatographic-tandem mass spectrometric method is described for the determination of metolazone in human blood. Metolazone was extracted from blood using ethyl acetate and separated on a C18 column interfaced with a triple quadrupole tandem mass spectrometer. The mobile phase consisting of a mixture of acetonitrile, 10 mmol/l ammonium acetate and formic acid (60:40:0.1, v/v/v) was delivered at a flow rate of 0.5 ml/min. Electrospray ionization (ESI) source was operated in positive ion mode. Selected reaction monitoring (SRM) mode using the transitions of m/z 366-->m/z 259 and m/z 321-->m/z 275 were used to quantify metolazone and the lorazepam (internal standard), respectively. The linearity was obtained over the concentration range of 0.5-500 ng/ml for metolazone and the lower limit of quantitation (LLOQ) was 0.5 ng/ml. For each level of QC samples, inter- and intra-run precision was less than 8.07 and 3.56% (relative standard deviation (RSD)), respectively, and the bias was within +/-4.0%. This method was successfully applied to the pharmacokinetic study of metolazone formulation after oral administration to humans.     

Quantitative determination of trimebutine maleate and its three metabolites in human plasma by liquid chromatography-tandem mass spectrometry

A sensitive and selective HPLC-MS-MS method was developed for the determination of trimebutine maleate (TM) and its major metabolites N-monodemethyltrimebutine (TM-MPB), N-didemethyltrimebutine (APB) and 3,4,5-trimethoxybenzoic acid (TMBA) in human plasma. The analytes were extracted from plasma samples by liquid-liquid extraction and chromatographed on a YMC J'sphere C(18) column. The mobile phase consisted of 2 mM ammonium acetate buffer (pH 6.5)-methanol (20:80, v/v), and at a flow-rate of 0.2 ml/min. Detection was carried out on a triple quadrupole tandem mass spectrometer in multiple reactions monitoring (MRM) mode using positive-negative switching electrospray ionization (ESI). The method was validated over the concentration range of 1-100 ng/ml for trimebutine maleate and APB, 1-500 ng/ml for MPB, and 50-10,000 ng/ml for TMBA. Inter- and intra-day precision (RSD%) for trimebutine maleate and its three metabolites were all within +/-15% and the accuracy was within 85-115%. The limit of quantitation was 1 ng/ml for trimebutine maleate, TM-MPB and APB, and 50 ng/ml for TMBA. The extraction recovery was on average 58.2% for trimebutine maleate, 69.6% for MPB, 51.2% for APB and 62.5% for TMBA. The method was applied to the pharmacokinetic study of trimebutine maleate and its metabolites in healthy Chinese volunteers.     

Simultaneous and sensitive determination of xanthotoxin,psoralen, isoimpinellin and bergapten in rat plasma by liquid chromatography–electrospray ionization mass spectrometry

A sensitive, specific and rapid liquid chromatography–mass spectrometry (LC–MS) method has been developed and validated for the simultaneous determination of xanthotoxin (8-methoxypsoralen), psoralen, isoimpinellin (5,8-dimethoxypsoralen) and bergapten (5-methoxypsoralen) in rat plasma using pimpinellin as an internal standard (IS). The plasma samples were pretreated by protein precipitation with methanol and chromatographic separation was performed on a C₁₈ column with a mobile phase composed of 1 mmol ammonium acetate and methanol (30:70, v/v). The detection was accomplished by multiple-reaction monitoring (MRM) scanning via electrospray ionization (ESI) source operating in the positive ionization mode. The optimized mass transition ion-pairs (m/z) for quantitation were 217.1/202.1 for xanthotoxin, 187.1/131.1 for psoralen, 247.1/217.0 for isoimpinellin, 217.1/202.1 for bergapten, and 247.1/231.1 for IS. The total run time was 6 min between injections. The calibration curves were linear over the investigated concentration range with all correlation coefficients higher than 0.998. The lower limits of quantitation (LLOQ) of these analytes were less than 1.21 ng/ml. The intra- and inter-day RSD were no more than 9.7% and the relative errors were within the range of ?8.1% to 4.5%. The average extraction recoveries for all compounds were between 90.7% and 106.2%. The proposed method was further applied to the determination of actual plasma samples from rats after oral administration of Radix Glehniae extract.     

Determination of three major components of bitespiramycin and their major active metabolites in rat plasma by liquid chromatography-ion trap mass spectrometry

The rapid, selective and sensitive liquid chromatographic-ion trap mass spectrometric (LC-MS(n)) method was developed and validated for determination of three major components (isovaleryspiramycins, ISV-SPMs) of a novel macrolide antibiotic bitespiramycin and their major active metabolites (spiramycins, SPMs) in rat plasma. The analytes ISV-SPMs, SPMs, internal standard roxithromycin and azithromycin were extracted from plasma samples by liquid-liquid extraction, and chromatographed on a C(18) column using two mobile phase systems. Detection was carried out on an ion trap mass spectrometer by selected reaction monitoring (SRM) mode via electrospray ionization (ESI). Three components (ISV-SPM I, II, III or SPM I, II, III) could be simultaneously determined within 6.5 min. Linear calibration curves were obtained in the concentration ranges of 4-200 ng/ml for ISV-SPM I and SPM I, 12-600 ng/ml for ISV-SPM II and SPM II, and 18-900 ng/ml for ISV-SPM III and SPM III. The intra- and inter-run precision (RSD), calculated from quality control (QC) samples were less than 8.8 and 10.4% for ISV-SPMs, and 9.3 and 11.2% for SPMs, respectively. The method was applied for the evaluation of the pharmacokinetics of bitespiramycin in rats following peroral/intravenous administration.     

Hydrophilic interaction liquid chromatography-tandem mass spectrometry for the determination of levosulpiride in human plasma

A rapid, sensitive and selective hydrophilic interaction liquid chromatography-tandem mass spectrometric (HILIC-MS/MS) method for the determination of levosulpiride in human plasma was developed. Levosulpiride and internal standard, tiapride were extracted from human plasma with ethyl acetate at pH 11 and analyzed on an Atlantis HILIC silica column with the mobile phase of acetonitrile-ammonium formate (190 mM, pH 3.0) (94:6, v/v). The analytes were detected using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The standard curve was linear (r = 0.999) over the concentration range of 1.00-200 ng/ml. The lower limit of quantification for levosulpiride was 1.00 ng/ml using 100 microl plasma sample. The coefficient of variation and relative error for intra- and inter-assay at three quality control (QC) levels were 3.8-9.1 and -2.9 to -0.1%, respectively. The recoveries of levosulpiride ranged from 80.5 to 87.4%, with that of tiapride (internal standard) being 84.6%. This method was successfully applied to the pharmacokinetic study of levosulpiride in humans.     

Determination of tiropramide in human plasma by liquid chromatography-tandem mass spectrometry

A rapid, sensitive and selective liquid chromatography-tandem mass spectrometric (LC/MS/MS) method for the determination of tiropramide in human plasma was developed. Tiropramide and internal standard, cisapride were extracted from human plasma by liquid-liquid extraction and analyzed on a Luna C8 column with the mobile phase of acetonitrile-ammonium formate (10mM, pH 4.5) (50:50, v/v). The analytes was detected using an electrospray ionization tandem mass spectrometry in the multiple-reaction-monitoring mode. The standard curve was linear (r=0.998) over the concentration range of 2.0-200 ng/ml. The intra- and inter-assay coefficients of variation ranged from 2.8 to 7.8 and 6.7 to 8.9%, respectively. The recoveries of tiropramide ranged from 50.2 to 53.1%, with that of cisapride (internal standard) being 60.9+/-5.3%. The lower limit of quantification for tiropramide was 2.0 ng/ml using 100 microl plasma sample. This method was applied to the pharmacokinetic study of tiropramide in human.