Positive Electrospray Tandem Mass Spectrometry Research Articles

Analysis of bisphenol A diglycidyl ether (BADGE) and its hydrolytic metabolites in biological specimens by high-performance liquid chromatography and tandem mass spectrometry.

Due to its cytotoxicity, genotoxicity, and adipogenicity observed in in vitro studies, bisphenol A diglycidyl ether (BADGE) may pose a health risk to humans. Quantifying BADGE exposure is an essential step to assess potential health risks associated with this ubiquitous compound widely used in certain plastic products. Due to the lack of endogenous sources for BADGE, bio-monitoring of BADGE and/or its hydrolytic metabolites (BADGE·H2O and BADGE·2H2O) can be a useful means to measure exposure. In this study, we developed a highly specific and sensitive method to measure BADGE, BADGE·H2O and BADGE·2H2O in plasma and urine, using a fast liquid-liquid extraction technique followed by a high-performance liquid chromatography and positive electrospray tandem mass spectrometry (LC-ESI-MS/MS) method. The method can quantify BADGE, BADGE·H2O and BADGE·2H2O with lower limits of quantification (LLOQ) of 0.05, 0.05 and 0.2 ng/ml, respectively. The percentage deviation of mean calculated concentrations from target concentrations was within 20%, variations across repeated analyses were within 15%, and mean extraction recovery was higher than 51.4% for all the three analytes in both plasma and urine matrices. The method has been applied to venous blood samples, cord blood samples, and urine samples collected from 9 to 14 adult volunteers. Results showed that concentrations of BADGE were lower than LLOQ in all of these samples except one urine sample. Low levels of BADGE·H2O from 0.108 to 0.222 ng/ml were observed in four venous blood samples and one urine sample (0.187 ng/ml). In contrast, concentrations of BADGE·2H2O were higher than LLOQ, varying from 0.660 to 303.593 ng/ml, in all the 10 venous blood samples and 1 cord blood sample (0.592 ng/ml) and two urine samples (0.200 and 0.306 ng/ml). The results suggest that bio-monitoring of blood and urine for BADGE exposure should focus on the hydrolysis derivatives of BADGE, mainly in the form of BADGE·2H2O.

Stability of the proteasome inhibitor bortezomib in cell based assays determined by ultra-high performance liquid chromatography coupled to tandem mass spectrometry

Bortezomib represents the first clinically approved proteasome inhibitor for multiple myeloma. Research conducted on its intracellular kinetics in target cells and on possibly related mechanisms of resistance is sparse so far. We therefore developed and validated a highly sensitive ultra-performance liquid chromatography coupled to tandem mass spectrometry (UPLC/MS/MS) method for bortezomib quantification within cultured myeloma cells and media. Fast gradient UPLC based on a BEH C18 column (1.7μm particle size) with aqueous formic acid and acetonitrile as mobile phase. Selective extraction procedures using protein precipitation extraction (PPE) and liquid–liquid extraction (LLE) were established and compared. Extracted bortezomib was quantified by positive electrospray tandem mass spectrometry using deuterated D8-bortezomib as internal standard. The calibrated ranges were 0.5–2500pg per sample. For LLE, overall accuracies varied between 99.2% and 112% (medium) and 89.9% and 111% (cells), while overall precision ranged from 1.13% to 13.0% (medium) and 2.80% to 12.7% (cells), respectively. Recovery rates (cells/medium) were >77%/>65% for LLE and >89%/63% for PPE. Matrix effects were generally lower for LLE compared to PPE. Regardless of the extraction method, retrievable amounts of bortezomib were considerably reduced after 24h of incubation (0.2, 1, 5, and 25nM). Revealing greater dependence on the extent of acidification, retrieval of bortezomib can be increased distinctly in acidified solution or acidified culture medium. Thus, particular attention needs to be paid to the occurring bortezomib degradation in neutral culture medium since correct quantification of intracellular bortezomib can only be achieved in relation to the corresponding extracellular concentration.

Liquid Chromatography/Electrospray Ionisation Tandem Mass Spectrometric Study of Sitagliptin and its Stressed Degradation Products

A sensitive UPLC positive ion electrospray tandem mass spectrometry method was developed and validated for identification of degradation products of sitagliptin formed during stress study. Six of the major degradants were identi-fied with the proposed method. The separation of sitagliptin and its degradation products was achieved on a Acquity BEH C-18 column (50×2.1 mm, 1.7 µm) using a gradient programme. The mobile phase consists of solvent A (10 mM ammonium formate, pH 6.4 adjusted with formic acid) and solvent B (acetonitrile) and quantitative evaluation was performed at 267 nm with a flow rate of 0.15 mL min(-1). Suitability of this method for the quantitative determination of the drugs was proved by validation in accordance with International Conference on Harmonization (ICH) guidelines and can be used for routine analysis of sitagliptin formulations in quality control.

Pharmacokinetics and liver distribution study of unbound curdione and curcumol in rats by microdialysis coupled with rapid resolution liquid chromatography (RRLC) and tandem mass spectrometry

A sensitive, specific, convenient and endogenous interference-free microdialysis sampling method coupled with RRLC–MS was successfully developed and applied to the determination of protein-unbound curdione and curcumol in biological samples. Microdialysis probes were simultaneously inserted into the jugular vein toward heart and the median lobe near the center of liver of rats under anesthesia. The separation was accomplished on a Zorbax SB-C18 column (2.1mm×50mm, 1.8μm) with a gradient elution and chromatography was conducted with RRLC system. Analytes were detected by positive ion electrospray tandem mass spectrometry and quantified on the basis of extracted ion chromatography (EIC) peak area signal. The calibration curves were linear over the range of 3.3–213.2ng/mL for curdione and 8.1–519.2ng/mL for curcumol. All the validation data, such as accuracy, precision, stability and matrix effect were satisfactory and within the required limits. The validated method was successfully applied to the pharmacokinetic study of curdione and curcumol in rat blood and liver after oral administration of Rhizoma Curcumae extracts. The results could provide a meaningful basis for better understanding of the intracorporal process of Rhizoma Curcumae, which would be helpful for further study both in clinic and laboratory.

Quantification of vorinostat and its main metabolites in plasma and intracellular vorinostat in PBMCs by liquid chromatography coupled to tandem mass spectrometry and its relation to histone deacetylase activity in human blood

Vorinostat (suberoylanilide hydroxamic acid) is the first approved histone deacetylase (HDAC) inhibitor for the treatment of cutaneous T-cell lymphoma after progressive disease following two systemic therapies. Intracellular access of vorinostat is essential to exert its epigenetic effects. Therefore, we studied the relationship between vorinostat extracellular (plasma) and intracellular (peripheral blood mononuclear cells, PBMCs) concentration and assessed its concentration-effect relationship by HDAC activity testing. Assays were developed and validated for the low nanomolar quantification of vorinostat and two inactive metabolites in human plasma and PBMCs. For the vorinostat extraction from plasma and PBMCs solid-phase extraction and liquid-liquid extraction methods were applied. Extraction recoveries ranged from 88.6% to 114.4% for all analytes and extraction methods. Extracts were chromatographed on a Phenomenex Luna column isocratically (plasma) or by gradient (PBMCs) consisting of acidic ammonium acetate, acetonitrile, and methanol. The analytes were quantified using deuterated internal standards and positive electrospray tandem mass spectrometry (multiple reaction monitoring) with lower limits of quantification of 11.0 ng/mL (plasma) and 0.1 ng/3 × 10(6) cells (PBMCs). The calibrated ranges were linear for vorinostat in plasma 11.0-1100 (11,000) ng/mL (metabolites) and PBMCs 0.1-10.0 ng/3 × 10(6) cells with correlation coefficients >0.99, an overall accuracy varying between -6.7% and +3.8% in plasma, -8.1% and -1.5% in PBMCs, and an overall precision ranging from 3.2% to 6.1% in plasma and 0.8% to 4.0% in PBMCs (SD batch-to-batch). The application to blood samples from healthy volunteers incubated with vorinostat revealed accumulation of vorinostat in PBMCs, effective intracellular HDAC inhibition at therapeutic vorinostat concentrations and a direct vorinostat concentration dependency to HDAC inhibition.

Application of a stabilizer cocktail of N-ethylmaleimide and phenylmethanesulfonyl fluoride to concurrently stabilize the disulfide and ester containing compounds in a plasma LC–MS/MS assay

BMS-753493, a conjugate of the active epothilone moiety, BMS-748285, to folic acid, has been evaluated for the treatment of cancer. The presence of a disulfide bond in BMS-753493 and an ester group in both BMS-753493 and BMS-748285 results in their being unstable in blood or plasma. A stabilization strategy using a cocktail of N-ethylmaleimide and phenylmethanesulfonyl fluoride was developed and applied to stabilize both analytes in human blood during sample collection, processing, and storage. A rugged and accurate LC–MS/MS method was developed and validated for the quantitation of BMS-753493 and its active moiety, BMS-748285, in human plasma. The stabilized plasma samples were extracted by protein precipitation. Chromatographic separation was achieved on a Luna C8 analytical column with a gradient elution. Analytes and their stable isotope labeled internal standards were detected by positive ion electrospray tandem mass spectrometry. The standard curves, which ranged from 10.0 to 5000ng/mL for BMS-753493 and from 1.00 to 500ng/mL for BMS-748285, were fitted to a 1/x2 weighted linear regression model. The intra-assay precision was within ±2.0% CV and inter-assay precision was within ±2.8% CV for both analytes. The assay accuracy was within ±4.6% of the nominal values for both analytes. Assay recoveries were high (∼80% for BMS-753493 and ∼100% for BMS-748285) and internal standard normalized matrix effects were minimal. Both analytes were stable in stabilized human plasma for at least 24h at room temperature, 231 days at −20°C, and following four freeze–thaw cycles. Incurred sample reanalysis played an important role in identifying a potential stability liability of the assay and helped improve the assay quality and robustness. The validated method was successfully applied to sample analysis in Phase I clinical studies.

Combined quantification of paclitaxel, docetaxel and ritonavir in human feces and urine using LC‐MS/MS

A combined assay for the determination of paclitaxel, docetaxel and ritonavir in human feces and urine is described. The drugs were extracted from 200 μL urine or 50 mg feces followed by high-performance liquid chromatography analysis coupled with positive ionization electrospray tandem mass spectrometry. The validation program included calibration model, accuracy and precision, carry-over, dilution test, specificity and selectivity, matrix effect, recovery and stability. Acceptance criteria were according to US Food and Drug Administration guidelines on bioanalytical method validation. The validated range was 0.5-500 ng/mL for paclitaxel and docetaxel, 2-2000 ng/mL for ritonavir in urine, 2-2000 ng/mg for paclitaxel and docetaxel, and 8-8000 ng/mg for ritonavir in feces. Inter-assay accuracy and precision were tested for all analytes at four concentration levels and were within 8.5% and <10.2%, respectively, in both matrices. Recovery at three concentration levels was between 77 and 94% in feces samples and between 69 and 85% in urine samples. Method development, including feces homogenization and spiking blank urine samples, are discussed. We demonstrated that each of the applied drugs could be quantified successfully in urine and feces using the described assay. The method was successfully applied for quantification of the analytes in feces and urine samples of patients.

English

erminalia ivoriensis&nbsp;A. Chev.&nbsp;(Combretaceae) is an Ivorian medicinal plant. There is little ethnobotanical and almost no chemical information available for this species. The aim of this study was to isolate phenolic compounds from&nbsp;T. ivoriensis. In this way, its ethyl acetate extract (Ea) was fractionated by silica gel column chromatography followed by Sephadex LH20 filtration. Elution solvents were methanol (MeOH), methylene chloride (Mc) and ethyl acetate (EtOAc). Analysis of the obtained fractions (F1-F4) by liquid chromatography coupled to positive electro-spray ionization tandem mass spectrometry (LC-ESI-MS/MS) afforded six known polyphenols: 1) 3,3&#39;-di-O-methylellagic acid); 2) 3,7,8-tri-O-methylellagic acid; 3) Progallin A; 4)&nbsp;3,3&#39;,4-O-Trimethyl-4&#39;-O-&beta;-D- glucopyranosylellagic acid; 5)&nbsp;Punicalagin and 6) Punicalin. All these natural products were isolated here for the first time from this plant. They presented various biological activities among which were anti-inflammatory, antioxidant and anti-HIV activities. Keywords:&nbsp;Terminalia,&nbsp;ivoriensis, LC-ESI-MS, isolation, characterization, polyphenols, activity, anti-inflammatory, antioxidant, anti-HIV.

Differentiation of isomeric β‐(1–4) hexose disaccharides by positive electrospray tandem mass spectrometry

Differentiation of isomeric β‐(1–4) hexose disaccharides by positive electrospray tandem mass spectrometry

A validated HPLC–MS/MS assay for quantifying unstable pharmacologically active metabolites of clopidogrel in human plasma: Application to a clinical pharmacokinetic study

Clopidogrel is prescribed for the treatment of Acute Coronary Syndrome and recent myocardial infarction, recent stroke, or established peripheral arterial disease. A sensitive and reliable high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) assay was developed and validated to enable reliable quantification of four diastereomeric and chemically reactive thiol metabolites, two of which are pharmacologically active, in human plasma. The metabolites were stabilized by alkylation of their reactive thiol moieties with 2-bromo-3'-methoxyacetophenone (MPB). Following organic solvent mediated-protein precipitation in a 96-well plate format, chromatographic separation was achieved by gradient elution on an Ascentis Express RP-amide column. Chromatographic conditions were optimized to ensure separation of the four derivatized active metabolites. Derivatized metabolites and stable isotope-labeled internal standards were detected by positive ion electrospray tandem mass spectrometry. The HPLC-MS/MS assay was validated over concentration ranges of 0.125-125 ng/mL for metabolites H1-H3 and 0.101-101 ng/mL for H4. Intra- and inter-assay precision values for replicate quality control samples were within 14.3% for all analytes during the assay validation. Mean quality control accuracy values were within ±6.3% of nominal values for all analytes. Assay recoveries were high (>79%). The four derivatized analytes were stable in human blood for at least 2 h at room temperature and on ice. The analytes were also stable in human plasma for at least 25 h at room temperature, 372 days at -20 °C and -70 °C, and following at least five freeze-thaw cycles. The validated assay was successfully applied to the quantification of all four thiol metabolites in human plasma in support of a human pharmacokinetic study.

A rugged and accurate liquid chromatography–tandem mass spectrometry method for the determination of asunaprevir, an NS3 protease inhibitor, in plasma

Asunaprevir (BMS-650032) is a potent hepatitis C virus (HCV) non-structural protein protease inhibitor currently in Phase III clinical trials for the treatment of HCV infection. A rugged and accurate LC-MS/MS method was developed and validated for the quantitation of asunaprevir in rat, dog, monkey, rabbit and mouse plasma. A systematic method screening and optimization strategy was applied to achieve optimized mass spectrometry, chromatography, and sample extraction conditions. The validated method utilized stable-isotope labeled D9-asunaprevir as the internal standard. The samples were extracted by liquid-liquid extraction using 10% ethyl acetate in hexane. Chromatographic separation was achieved with gradient elution on a Waters Atlantis dC18 analytical column. Analyte and its internal standard were detected by positive ion electrospray tandem mass spectrometry. The standard curve, which ranged from 5.00 to 2000ng/mL for asunaprevir, was fitted to a 1/x(2) weighted linear regression model. The intra-assay precision was within ±3.6% CV, inter-assay precision was within ±4.0% CV, and the assay accuracy was within ±8.1% of the nominal values in all the species. The method was successfully applied to support multiple pre-clinical toxicokinetic studies in different species.

Simultaneous determination of azathioprine and its metabolite 6-mercaptopurine in human plasma using solid phase extraction-evaporation and liquid chromatography–positive electrospray tandem mass spectrometry

A simple, rapid, specific, sensitive and liquid chromatography coupled with tandem mass spectrophotometric method was developed and validated for the estimation of azathioprine and its metabolite 6-mercaptopurine in human plasma by using lamivudine and 6-mercaptopurine D3 as the internal standard. Azathioprine and 6-mercaptopurine were extracted from human plasma by solid-phase extraction (SPE)-Evaporation method, using Oasis MCX cartridge for cleaning procedure. The stationary phase was chromatographed on a ZORBAX SB CN, (75X50 mm, 5 µ) column where as mobile phase constitutes of acetonitrile: 2mM ammonium acetate (70:30 v/v) at a flow rate of 0.800 ml/min. The detection was performed with an Applied Biosystems Sciex API 4000 mass spectrometer by multiple reaction monitoring (MRM). The method validation proofs were carried out as per the USFDA guidelines as described, showing a linearity system (r2 &gt; 0.99) over a range of 2.455 ng/mL to 106.568 ng/mL for azathioprine and 1.165 ng/mL to 101.143 ng/mL concentrations for 6-mercaptopurine and a recovery shows 99.36% and 100.44% for azathioprine and 6-mercaptopurine respectively. The results show that this proposed approach is effective and can be applied to the extraction and analysis of other pharmaceutical compounds.DOI: http://dx.doi.org/10.3329/icpj.v1i11.12059 International Current Pharmaceutical Journal 2012, 1(11): 342-352

A validated enantioselective LC–MS/MS assay for the simultaneous determination of carvedilol and its pharmacologically active 4′-hydroxyphenyl metabolite in human plasma: Application to a clinical pharmacokinetic study

Carvedilol is widely prescribed for the treatment of hypertension, heart failure and left ventricular dysfunction following myocardial infarction. A sensitive and reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay was developed and validated to enable reliable and efficient bioanalysis of the (R)- and (S)-enantiomers of carvedilol and its pharmacologically active 4'-hydroxyphenyl metabolite in human plasma. Following plasma extraction using supported liquid extraction (SLE) in a 96-well plate format, extracted samples were derivatized with 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl isothiocyanate (GITC). Chromatographic separation was achieved by gradient elution on an ACQUITY UPLC HSS T3 analytical column. The impact of several potentially interfering isobaric metabolites on the quantification of the 4'-hydroxyphenyl metabolite (R)- and (S)-enantiomers was minimized by implementation of a combination of chromatographic and mass spectrometric techniques. Derivatized analytes and stable-labeled internal standards were detected by positive ion electrospray tandem mass spectrometry. The assay was validated over concentration ranges of 0.200-100 ng/mL for (R)- and (S)-carvedilol and 0.0200-10.0 ng/mL for (R)- and (S)-4'-hydroxyphenyl carvedilol. Intra- and inter-assay precision values for replicate quality control samples were within 11.9% for all analytes during the assay validation. Mean quality control accuracy values were within ±9.4% of nominal values for all analytes. Assay recoveries were high (>76%) and internal standard normalized matrix effects were minimal. The four analytes were stable in human plasma for at least 24 h at room temperature, 89 days at -20 °C and -70 °C, and following at least five freeze-thaw cycles. The validated assay was successfully applied to the quantification of the (R)- and (S)-enantiomers of both carvedilol and its pharmacologically active 4'-hydroxyphenyl metabolite in human plasma in support of a human pharmacokinetic study.

Validation of a dried blood spot LC–MS/MS approach for cyclosporin A in cat blood: Comparison with a classical sample preparation

A rapid, selective and sensitive bioanalytical method was developed and validated for cyclosporin A (CsA) in cat blood samples using dried blood spot (DBS) coupled with high pressure liquid chromatography hyphenated to positive electrospray tandem mass spectrometry (HPLC-ESI-MS/MS). CsA was quantified using a structural analog cyclosporin D (CsD) as internal standard in multiple reaction monitoring mode (MRM) using the transitions 1220→1203 for CsA and 1234→1217 for CsD. A 5-μL blood aliquot was spotted onto a DBS card, then after a drying step, blood spots were punched out from the cards and extracted with MeOH before injection into a LC-MS/MS system. The linear range of the method was 5-2000 ng/mL, with accuracy and precision within the FDA acceptance criteria (i.e., ±15% and ±20% for the lowest level). In the study presented herein a comparison was made between this new methodology, based on the use of DBS, and a previously developed solid phase extraction (SPE) procedure, applied to blood samples from a cat pharmacokinetic study. Good correlation (r(2)=0.97) was demonstrated between the data obtained with the two methods. The DBS methodology revealed to be cheaper, faster, less solvent-consuming and requiring less blood volume from animals than the previous SPE method. Thus, the proposed HPLC-ESI-MS/MS method, based on DBS, has demonstrated to be a suitable and advantageous approach for the analysis of CsA in cat blood.

Quantification of femtomolar concentrations of the CYP3A substrate midazolam and its main metabolite 1′-hydroxymidazolam in human plasma using ultra performance liquid chromatography coupled to tandem mass spectrometry

The benzodiazepine midazolam is a probe drug used to phenotype cytochrome P450 3A activity. In this situation, effective sedative concentrations are neither needed nor desired, and in fact the use of very low doses is advantageous. We therefore developed and validated an assay for the femtomolar quantification of midazolam and 1'-hydroxymidazolam in human plasma. Plasma (0.25 mL) and 96-well-based solid-phase extraction were used for sample preparation. Extraction recoveries ranged between 75 and 92% for both analytes. Extracts were chromatographed within 2 min on a Waters BEH C18 1.7 μm UPLC® column with a fast gradient consisting of formic acid, ammonia, and acetonitrile. Midazolam and 1'-hydroxymidazolam were quantified using deuterium- and (13)C-labeled internal standards and positive electrospray tandem mass spectrometry in the multiple reaction monitoring mode, which yielded lower limits of quantification of 50 fg/mL (154 fmol/L) and 250 fg/mL (733 fmol/L) and a corresponding precision of <20%. The calibrated concentration ranges were linear for midazolam (0.05-250 pg/mL) and 1'-hydroxymidazolam (0.25-125 pg/mL), with correlation coefficients of >0.99. Within-batch and batch-to-batch precision in the calibrated ranges for both analytes were <14% and <12%. No ion suppression was detectable, and plasma matrix effects were minimized to <15% (<25%) for midazolam (1'-hydroxymidazolam). The assay was successfully applied to assess the kinetics of midazolam in two human volunteers after the administration of single oral microgram doses (1-100 μg). This ultrasensitive assay allowed us to quantify the kinetics of midazolam and 1'-hydroxymidazolam for at least 10 h, even after the administration of only 1 μg of midazolam.

A validated LC–MS/MS assay for the simultaneous determination of the anti-leukemic agent dasatinib and two pharmacologically active metabolites in human plasma: Application to a clinical pharmacokinetic study

Dasatinib (Sprycel ®) is a potent antitumor agent prescribed for patients with chronic myeloid leukemia (CML). To enable reliable quantification of dasatinib and its pharmacologically active metabolites in human plasma during clinical testing, a sensitive and reliable liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed and validated. Samples were prepared using solid phase extraction on Oasis HLB 96-well plates. Chromatographic separation was achieved isocratically on a Luna phenyl–hexyl analytical column. Analytes and the stable labeled internal standards were detected by positive ion electrospray tandem mass spectrometry. The assay was validated over a concentration range of 1.00–1000 ng/mL for dasatinib and its two active metabolites. Intra- and inter-assay precision values for replicate QC control samples were within 5.3% for all analytes during the assay validation. Mean QC control accuracy values were within ±9.0% of nominal values for all analytes. Assay recoveries were high (>79%) and internal standard normalized matrix effects were minimal. The three analytes were stable in human plasma for at least 22 h at room temperature, for at least 123 days at −20 °C, and following at least six freeze–thaw cycles. The validated method was successfully applied to the quantification of dasatinib and two active metabolites in a human pharmacokinetic study.

A sensitive combined assay for the quantification of paclitaxel, docetaxel and ritonavir in human plasma using liquid chromatography coupled with tandem mass spectrometry

A combined assay for the determination of paclitaxel, docetaxel and ritonavir in human plasma is described. The drugs were extracted from 200 μL human plasma using liquid–liquid extraction with tertiar-butylmethylether, followed by high performance liquid chromatography analysis using 10 mM ammonium hydroxide pH 10:methanol (3:7, v/v) as mobile phase. Chromatographic separation was obtained using a Zorbax Extend C 18 column. Labelled analogues of the analytes are used as internal standards. For detection, positive ionization electrospray tandem mass spectrometry was used. Method development including optimisation of the mass transitions and response, mobile phase optimisation and column selection are discussed. The method was validated according to FDA guidelines and the principles of Good Laboratory Practice (GLP). The validated range was 0.5–500 ng/mL for paclitaxel and docetaxel and 2–2000 ng/mL for ritonavir. For quantification, quadratic calibration curves were used ( r 2 > 0.99). The total runtime of the method is 9 min and the assay combines analytes with differences in ionisation and desired concentration range. Inter-assay accuracy and precision were tested at four concentration levels and were within 10% and less than 10%, respectively, for all analytes. Carry-over was less than 6% and endogenous interferences or interferences between analytes and internal standards were less than 20% of the response at the lower limit of quantification level. The matrix factor and recovery were determined at low, mid and high concentration levels. The matrix factor was around 1 for all analytes and total recovery between 77.5 and 104%. Stability was investigated in stock solutions, human plasma, dry extracts, final extracts and during 3 freeze/thaw cycles. The described method was successfully applied in clinical studies with oral administration of docetaxel or paclitaxel in combination with ritonavir.

Determination of vitamins A, D and E in a small volume of human plasma by a high‐throughput method based on liquid chromatography/tandem mass spectrometry

We have developed an automated high-throughput assay for the determination of vitamin A (retinol), ergocalciferol (25-OH D2), cholecalciferol (25-OH D3) and vitamin E (α-tocopherol) in a small volume of human plasma. Sample preparation involved mixing 50 μL of plasma with 100 μL of ethanol containing isotope-labelled internal standards, followed by mixing with isooctane/chloroform (3:1, 300 μL). The organic phase was evaporated, and the sample reconstituted in 50 μL methanol. The analysis was performed using reversed-phase liquid chromatography with a gradient mobile phase containing water, methanol and ammonium formate. Chromatographic run-time was 5 min, and positive mode electrospray tandem mass spectrometry (MS/MS) was used for detection. The limits of detection were 0.10 μM for all-trans retinol and 3.3 nM for 25-OH D2 and 25-OH D3. Recoveries were 91.9-105.0%, and within- and between-day coefficients of variance (CVs) 2.4-5.3 and 3.1-8.2, respectively. The assay is presently being used in large-scale studies.

Quantification of cinacalcet by LC–MS/MS using liquid–liquid extraction from 50 μL of plasma

A simple and economical high-performance liquid chromatography–positive ion electrospray tandem mass spectrometry method was developed and validated for the quantification of cinacalcet in plasma. Following liquid–liquid extraction, the analyte was separated using an isocratic mobile phase on a reversed-phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective [M+H] + ions, m/ z 358–155 for cinacalcet and m/ z 310–148 for the internal standard. The assay exhibited a linear dynamic range of 0.1–200 ng/mL for cinacalcet in plasma. Acceptable precision (<10%) and accuracy (100 ± 5%) were obtained for concentrations over the standard curve range. A run time of 3.5 min for each sample made it possible to analyze more than 250 samples per day. The method was successfully applied to quantify cinacalcet concentrations in a preclinical pharmacokinetic study after a single oral administration of cinacalcet at 10 mg/kg to rats. Following oral administration the maximum mean concentration in plasma ( C max; 160 ± 56 ng/mL) was achieved at 1.0 h ( T max), area under the curve (AUC) and half-life ( t 1/2) were 949 ± 257 ng h/mL and 3.58 ± 0.4 h, respectively.

A sensitive high performance liquid chromatography–positive electrospray tandem mass spectrometry method for N7-[2-[(2-hydroxyethyl)thio]-ethyl]guanine determination

A simple, fast, sensitive and robust method for the determination of the sulfur mustard (SM) exposure biomarker– N 7-[2-[(2-hydroxyethyl)thio]-ethyl]guanine (HETEG) was reported using high-performance liquid chromatography–positive electrospray tandem mass spectrometry (HPLC–ESI-MS/MS), working in multiple reaction monitor (MRM) mode. The method provided limit of detection of 0.330 ng/mL and lower limit of quantitation of 0.940 ng/mL. The method was linearly calibrated from 0.940 ng/mL to 587 ng/mL with precisions of 3.5–14.5%, and accuracies of 88–112%. The recovery varied from 102% to 118%. HETEG spiked in DNA hydrolytes isolated from the human whole blood was stable after five freeze/thaw cycles and 35-day frozen at −20 °C. For the exposed biological samples, alkylated DNA was isolated from SM-treated human whole blood, followed by DNA digestion and adducts enrichment, the resulting alkylation base was determined. By the procedure, the HETEG level in DNA hydrolytes isolated from the human whole blood exposure to 312 ng/mL SM was detected successfully.