Journal of Chromatography B (v.878, #19)

Limited stability of thiopurine metabolites in blood samples: Relevant in research and clinical practise by P. de Graaf; R.M. Vos; N.H.K. de Boer; A. Sinjewel; B. Jharap; C.J.J. Mulder; A.A. van Bodegraven; A.I. Veldkamp (1437-1442).
Monitoring of thiopurine metabolites 6-thioguanine nucleotides (6-TGN) and 6-methylmercaptopurine (6-MMP) is used to assess compliance and explain adverse reactions in IBD-patients. Correlations between dosage, metabolite concentrations and therapeutic efficacy or toxicity are contradictive. Research is complicated by analytical problems as matrices analyzed and analytical procedures vary widely. Moreover, stability of thiopurine metabolites is not well documented, yet pivotal for interpretation of analytical outcomes. Therefore, we prospectively investigated metabolite stability in blood samples under standard storage conditions.Stability at room temperature and refrigeration (22 °C, 4 °C) was investigated during 1 week and frozen samples (−20 °C, −80 °C) were analyzed during 6 months storage. Ten patient samples were analyzed for each study period.Median 6-TGN concentrations on day 7 decreased significantly to 53% and 90% during storage at ambient temperature or refrigeration. Median 6-MMP concentrations on day 7 decreased significantly to 55% and 86%, respectively. Samples stored at −20 °C also showed significant decreases in both 6-TGN and 6-MMP in comparison with baseline values. At −80 °C, only 6-MMP showed a significant decrease in values compared to baseline.The stability of thiopurine metabolites is clearly a limiting factor in studies investigating utilisation of TDM and correlations with therapeutic outcome in IBD-patients. This has to be accounted for in clinical practice and (multi-center) trials investigating thiopurine drugs.
Keywords: Inflammatory bowel disease; Azathioprine; 6-Mercaptopurine; Clinical pharmacology; Therapeutic drug monitoring; 6-Thioguanine; 6-Thioguanine nucleotides; 6-Methylmercaptopurine; Chemical stability; Patient blood samples;

Determination of epitestosterone in human urine by off-line immunoaffinity solid-phase extraction coupled with high performance liquid chromatography by Li Xu; Shuang Qiu; Cui-Jin Sun; Qin-Pei Deng; Hong-Xu Chen; Ying-Lin Zhou; Xin-Xiang Zhang (1443-1448).
Epitestosterone (ET) has been used as a masking agent and prohibited by the World Anti-Doping Agency (WADA) because its administration will decrease the urinary T/ET ratio, a marker of testosterone (T) administration. In this study, an off-line immunoaffinity extraction coupled with high performance liquid chromatography (HPLC) was developed to quantify the endogenous steroid ET in human urine. The immunoaffinity column (IAC) was prepared by immobilizing the anti-ET monoclonal antibodies on CNBr-activated Sepharose 4B, which can remove the contaminations and non-target compounds from matrix to enrich the target analyte ET. The mobile phase was ammonium acetate (10 mM, pH 4.0)/acetonitrile (45/55, v/v) at an isocratic flow of 1.0 mL/min and the UV absorbance detection wavelength was 244 nm for the detection of ET. The IAC showed good reliability and durability since it had been used for more than 100 runs in a year. The limit of quantification (LOQ) was 1 ng/mL. Satisfied repeatability and precision of the day-to-day and within-day were obtained with the RSD values less than 10%. Results of the recovery of the urine samples were ranged from 98% to 102% with repeatability less than 9%, indicating that the method developed can be used for the real urine sample analysis.
Keywords: Epitestosterone; Immunoaffinity extraction; High performance liquid chromatography;

We describe a novel high performance liquid chromatography–electrospray ionization mass spectrometry (HPLC–ESI-MS) method for the simultaneous quantification of enzymatic immature (dihydroxylysinonorleucine DHLNL, hydroxylysinonorleucine HLNL) and mature (pyridinoline PYD, deoxypyridinoline DPD) collagen crosslinks in connective tissues. The crosslinks were separated on a C18 Atlantis® T3 reversed-phase column with heptafluorobutyric acid (HFBA) as volatile ion-pairing reagent in an acetonitrile–water mobile phase. Detection was carried out by electrospray ionization mass spectrometry in a positive ion mode with selected ion recording (SIR). This method is more sensitive and selective than ion exchange chromatography with post-column ninhydrin detection which is the reference method used for the simultaneous quantification of collagen enzymatic divalent and trivalent crosslinks. The intra and inter-day precision errors were less than 3.4 and 7.7%, respectively for DHLNL, 3.5 and 5.9%, respectively for HLNL, 4.0 and 5.2%, respectively for PYD, 8.2 and 10.7%, respectively for DPD. This novel technique should be useful to quantify simultaneously DHLNL, HLNL, PYD and DPD in connective tissues and to evaluate the maturation of collagen by determination of the ratio between immature and mature enzymatic crosslinks.
Keywords: Pyridinium crosslinks; Immature crosslinks; Collagen crosslinks; Dihydroxylysinonorleucine; Hydroxylysinonorleucine; HPLC–MS;

Clinical pharmacokinetic studies of antiretrovirals require accurate and precise measurement of plasma drug concentrations. Here we describe a simple, fast and sensitive HPLC–MS/MS method for determination of the commonly used protease inhibitors (PI) amprenavir, atazanavir, darunavir, lopinavir, ritonavir, saquinavir and the non-nucleoside reverse transcriptase inhibitor (NNRTI) nevirapine, as well as the more recent antiretrovirals, the CCR5 antagonist maraviroc and the “second generation” NNRTI etravirine and rilpivirine. An internal standard (quinoxalone; QX) was added to plasma aliquots (100 μl) prior to protein precipitation with acetonitrile (500 μl) followed by centrifugation and addition of 0.05% formic acid (200 μl) to the supernatant. Chromatographic separation was achieved using a gradient (acetonitrile and 0.05% formic acid) mobile phase on a reverse-phase C18 column. Detection was via selective reaction monitoring (SRM) operating in positive ionization mode on a triple-quadrupole mass spectrometer. All compounds eluted within a 5 min run time. Calibration curves were validated over concentration ranges reflecting therapeutic concentrations observed in HIV-infected patients from pharmacokinetic data reported in the literature. Correlation coefficients (r 2) exceeded 0.998. Inter- and intra-assay variation ranged between 1% and 10% and % recovery exceeded 90% for all analytes. The method described is being successfully applied to measure plasma antiretroviral concentrations from samples obtained from clinical pharmacokinetic studies.
Keywords: HPLC–MS/MS; Protein precipitation; Protease inhibitors; Etravirine; Rilpivirine; Maraviroc;

Analysis of intracellular doxorubicin and its metabolites by ultra-high-performance liquid chromatography by Kumiko Sakai-Kato; Eiko Saito; Keiko Ishikura; Toru Kawanishi (1466-1470).
Doxorubicin, a highly effective anticancer drug, produces severe side effect such as cardiotoxicity, which is mainly caused by its metabolite, doxorubicinol. While in vitro studies by measuring cellular concentration of doxorubicin have been reported, there have been no reports on measuring cellular concentration of the metabolites. In this report, we developed a sensitive and high-throughput method for measuring cellular concentrations of doxorubicin and its metabolites by ultra-high-performance liquid chromatography. The method achieved more than 96% recovery of doxorubicin and its metabolites from cell homogenates. Using simple separation conditions, doxorubicin and its three main metabolites, and the internal standard, were separated within 3 min. The method has a limit of quantification of 17.4 pg (32.0 fmol) injected doxorubicin. This high sensitivity enables the detection and intracellular quantification of doxorubicin and its metabolite, doxorubicinol, in cell homogenates, and its use will facilitate studies of the relationship between doxorubicin pharmacokinetics and therapeutic outcome.
Keywords: Ultra-high-performance liquid chromatography; Doxorubicin; Doxorubicinol;

This paper presents the development of a simple liquid chromatography–tandem mass spectrometry (LC–MS/MS) method to determine corticosteroids in bovine urine sample matrices. This method uses a single phase extraction (SPE) for cleaning of the sample with an Oasis MAX cartridge at pH 9.0–9.5 and elution by a neutral organic solvent (acetonitrile/dichloromethane), followed by separation on a GEMINI C18 column in the gradient mode with acetate buffer (pH 4.1)/methanol. A triple quadrupole mass spectrometer equipped with a multimode ion source, set to negative atmospheric pressure chemical ionization (APCI) in the multiple reaction monitoring mode was used for detection. The main advantage of this method over other commonly used methods includes the use of SPE with a low volume cartridge for sample preparation and no ion suppression effects from matrix components of the urine samples in the LC–MS/MS analysis. This allowed a reduction the quantification limits (decision limits, CCα) for the first time to 0.1 μg/L (1 and 0.2 μg/L for triamcinolone and flumethasone, respectively). The developed method was validated in accordance with the European Union Commission Decision 2002/657 EC. The recoveries and within-laboratory reproducibility varied from 77% to 115% and 87% to 107.5%, respectively, at 2, 3, and 4 μg/L levels of corticosteroids. The relative standard deviation (RSD) of the measurements was lower than 30%. The decision limit was calculated by multiplying the signal-to-noise ratio by 3 and the obtained values were in the range of 0.1–1.0 μg/L, confirmed by the analysis of twenty blank samples, which were spiked at the desired concentrations. The detection capability was calculated by the addition of the decision limit and the standard deviation followed by multiplication by 1.64 of the within-laboratory reproducibility at 2 μg/L of corticosteroids. The method was applied to four urine samples, giving concentrations of prednisolone (PRED) residues in the range from 0.3 to 0.9 μg/L.
Keywords: Corticosteroid; Liquid chromatography–tandem mass spectrometry; Ion-suppression; Urine; Validation;

Simultaneous determination of clopidogrel and its carboxylic acid metabolite by capillary electrophoresis by Hugo Serra; Maria do Rosário Bronze; Ana Luísa Simplício (1480-1486).
A capillary electrophoresis method was developed and validated for the first time for the analysis of clopidogrel and its carboxylic acid metabolite. Prior to method optimization, the pH dependence of effective mobility of both compounds was determined in order to define the initial pH of the running buffer. The optimized method demonstrated to be selective, and linear in the concentration range of 2–100 μM for both compounds. The method limits of detection and quantification were, respectively, 1.2 and 3.7 μM for clopidogrel and 1.1 and 3.2 μM for the carboxylic acid metabolite. Moreover, method validation demonstrated acceptable results for method repeatability (RSD < 7%), intermediate precision (RSD < 7%) and accuracy (85–96%) and is suitable for the quantitative analysis of clopidogrel and its metabolite in serum samples. The validated method was also applied to the determination of the kinetic parameters of the enzymatic hydrolysis of clopidogrel. An apparent K m of 145 ± 30 μM and V max of 0.4, 1.5 and 3.4 μM/min, respectively for the enzyme concentrations 1.0, 2.0 and 4.0 U/ml, were obtained.
Keywords: Capillary electrophoresis; Clopidogrel; Carboxylic acid metabolite; Method validation;

Development, validation and comparison of LC–MS/MS and RIA methods for quantification of vertebrates-like sex-steroids in prosobranch molluscs by M. Gust; E. Vulliet; B. Giroud; F. Garnier; S. Couturier; J. Garric; T. Buronfosse (1487-1492).
The role of vertebrate-like sex-steroids (testosterone, T, progesterone, P, and 17β-estradiol, E2) in molluscs is still debated, but they could represent potential biomarkers of endocrine disruption. A radioimmunoassay (RIA) and a liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) methods have been developed and compared to measure their levels in a gastropod snail Potamopyrgus antipodarum. Both methods showed a good reproducibility despite the complex matrix and the very low levels of vertebrate-like sex-steroids. Only T and P were detected using the LC–MS/MS method, while the RIA method reached lower detection limits and enabled the detection of all three steroids. Results indicated that T and P were mainly present as unconjugated forms. Both methods were compared in the analysis of snails exposed to waste water treatment plant effluents and led to the same conclusions concerning the modulation of steroids levels. Moreover, they both were in agreement concerning T measurements. On the other hand, LC–MS/MS appeared to be more suitable when analyzing P levels due to a low sensitivity of the RIA method. As E2 was not measured using the LC–MS/MS method because of a higher detection limit compared to the other steroids, the results obtained with the RIA method should be interpreted with caution. LC–MS/MS remains the gold standard for sex-steroid determinations, however a relevant and alternative method based on RIA was developed, requiring fewer organisms. RIA seems a promising method as a screening tool for experimental use, allowing comparison of sex-steroid levels in the mudsnail both in laboratory and in field experiments.
Keywords: RIA; LC–MS/MS; Comparative analysis; Steroids; Potamopyrgus antipodarum;

Quantitative analysis of adenosine using liquid chromatography/atmospheric pressure chemical ionization-tandem mass spectrometry (LC/APCI-MS/MS) by Annelies Van Dycke; Alain Verstraete; Kristof Pil; Robrecht Raedt; Kristl Vonck; Detlev Boison; Paul Boon (1493-1498).
Adenosine-secreting cellular brain implants constitute a promising therapeutic approach for the treatment of epilepsy. To engineer neural stem cells for therapeutic adenosine delivery, a reliable and fast analytical method is necessary to quantify cell-based adenosine release. Here we describe the development, optimization and validation of adenosine measurement using liquid chromatography–atmospheric pressure chemical ionization-tandem mass spectrometry (LC–APCI-MS/MS). LC–MS/MS in positive ion mode used selected reaction monitoring at m/z of 268.2/136.1 and 302.2/170.0 for adenosine and the internal standard, respectively. The bias was within 15% of the nominal value and evaluation of precision showed a relative standard deviation lower than 15% for all measured concentrations. The lower limit of quantification of adenosine was 15.6 ng/ml. Freeze and thaw stability and processed sample stability also fulfilled the acceptance criteria. Evaluation of the matrix effect showed that the method is not affected by relative matrix effects. The major advantages of this method are the absence of an extraction phase and the combination of the high selectivity and sensitivity characteristic for the LC–MS/MS technique, with a short run time of 4.5 min. These results demonstrate that this method is a useful tool to measure adenosine concentrations in culture medium released from stem cells in vitro.
Keywords: Adenosine; Liquid chromatography; Tandem mass spectrometry; Stem cells;

Development and validation of a Sensitive bioanalytical method for the quantitative estimation of Pantoprazole in human plasma samples by LC–MS/MS: Application to bioequivalence study by Balasekhara R. Challa; Sai H.S. Boddu; Bahlul Z. Awen; Babu R. Chandu; Chandrasekhar K. Bannoth; Mukkanti Khagga; Kanchanamala Kanala; Rihana P. Shaik (1499-1505).
The present study aims at developing a simple, sensitive and specific liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the quantification of pantoprazole sodium (PS) in human plasma using pantoprazole D3 (PSD3) as internal standard (IS). Chromatographic separation was performed on Zorbax SB-C18, 4.6 mm × 75 mm, 3.5 μm, 80 Å column with an isocratic mobile phase composed of 10 mM ammonium acetate (pH 7.10): acetonitrile (30:70, v/v), pumped at 0.6 mL/min. PS and PSD3 were detected with proton adducts at m/z 384.2 → 200.1 and 387.1 → 203.1 in multiple reaction monitoring (MRM) positive mode, respectively. Precipitation method was employed in the extraction of PS and PSD3 from the biological matrix. This method was validated over a linear concentration range of 10.00–3000.00 ng/mL with correlation coefficient (r) ≥ 0.9997. Intra- and inter-day precision of PS were found to be within the range of 1.13–1.54 and 1.76–2.86, respectively. Both analytes were stable throughout freeze/thaw cycles, bench top and postoperative stability studies. This method was successfully utilized in the analysis of blood samples following oral administration of PS (40 mg) in healthy human volunteers.
Keywords: Mass spectrometry; Bioequivalence; Pantoprazole;

Automated mass spectrometric analysis of urinary free catecholamines using on-line solid phase extraction by Wilhelmina H.A. de Jong; Elisabeth G.E. de Vries; Bruce H.R. Wolffenbuttel; I.P. Kema (1506-1512).
Analysis of catecholamines (epinephrine, norepinephrine and dopamine) in plasma and urine is used for diagnosis and treatment of catecholamine-producing tumors. Current analytical techniques for catecholamine quantification are laborious, time-consuming and technically demanding. Our aim was to develop an automated on-line solid phase extraction method coupled to high performance liquid chromatography–tandem mass spectrometry (XLC–MS/MS) for the quantification of free catecholamines in urine. Five microlitre urine equivalent was pre-purified by automated on-line solid phase extraction, using phenylboronic acid complexation. Reversed phase (pentafluorophenylpropyl column) chromatography was applied. Mass spectrometric detection was operated in multiple reaction monitoring mode using a quadrupole tandem mass spectrometer with positive electrospray ionization. Urinary reference intervals were set in 24-h urine collections of 120 healthy subjects. XLC–MS/MS was compared with liquid chromatography with electrochemical detection (HPLC–ECD). Total run-time was 14 min. Intra- and inter-assay analytical variations were <10%. Linearity was excellent (R 2  > 0.99). Quantification limits were 1.47 nmol/L, 15.8 nmol/L and 11.7 nmol/L for epinephrine, norepinephrine and dopamine, respectively. XLC–MS/MS correlated well with HPLC–ECD (correlation coefficient >0.98). Reference intervals were 1–10 μmol/mol, 10–50 μmol/mol and 60–225 μmol/mol creatinine for epinephrine, norepinephrine and dopamine, respectively. Advantages of the XLC–MS/MS catecholamine method include its high analytical performance by selective PBA affinity and high specificity and sensitivity by unique MS/MS fragmentation.
Keywords: Catecholamines; Urine; PBA; Mass spectrometry; On-line SPE; XLC–MS/MS; Epinephrine; Norepinephrine; Dopamine;

Quantification of CLR1401, a novel alkylphosphocholine anticancer agent, in rat plasma by hydrophilic interaction liquid chromatography–tandem mass spectrometric detection by Hongliang Jiang; Michelle J. Cannon; Maria Banach; Anatoly N. Pinchuk; Giangthy N. Ton; Christie Scheuerell; Marc A. Longino; Jamey P. Weichert; Richard Tollefson; William R. Clarke; Qin C. Ji; Xiangyu Jiang (1513-1518).
A rapid and specific LC–MS/MS based bioanalytical method was developed and validated for the determination of 18-(p-iodophenyl)octadecyl phosphocholine (CLR1401), a novel phosphocholine drug candidate, in rat plasma. The optimal chromatographic behavior of CLR1401 was achieved on a Kromasil silica column (50 mm × 3 mm, 5 μm) under hydrophilic interaction chromatography. The total LC analysis time per injection was 2.8 min with a flow rate of 1.5 mL/min under gradient elution. Liquid–liquid extraction in a 96-well format using ethyl acetate was developed and applied for method validation and sample analysis. The method validation was conducted over the curve range of 2.00–1000 ng/mL using 0.0500 mL of plasma sample. The intra- and inter-day precision and accuracy of the quality control samples at low, medium, and high concentration levels showed ≤ 5.9% relative standard deviation (RSD) and −10.8 to −1.4% relative error (RE). The method was successfully applied to determine the toxicokinetics of CLR1401 in rats from three dose groups of 0.4, 4.0, and 10.0 mg/kg/day via intravenous administration.
Keywords: CLR1401; LC–MS/MS; Liquid–liquid extraction; Hydrophilic interaction chromatography; Alkyl phosphocholine;

The performance of three different affinity and immunoaffinity subtraction spin columns was investigated for the removal of the most abundant proteins in human cerebrospinal fluid (CSF). A pool of human CSF was processed with the spin columns and both the bound and flow through fractions were compared with each other and with intact CSF using 1D gel electrophoresis and nanoLC–MALDI-TOF/TOF-MS analysis. MASCOT MS/MS ionscores were compared before and after processing with the columns. The non-specific co-removal of proteins bound to the high abundant proteins, so called “sponge effect” was also examined for each spin column. The reproducibility of one of the spin columns, ProteomeLab IgY-12 proteome partitioning spin column, was further investigated by isobaric tags for relative and absolute quantification (iTRAQ) labeling and MS/MS analysis. Overall, 173 unique proteins were identified on a 95% MudPIT confidence scoring level. For all three spin columns, the number of proteins identified and their MASCOT scores were increased up to 10 times. The largest degree of non-specific protein removal was observed for a purely affinity based albumin removal column, where 28 other proteins also were present. The ProteomeLab IgY-12 proteome partitioning spin column showed very high reproducibility when combined with iTRAQ labeling and MS/MS analysis. The combined relative standard deviation (R.S.D.) for the high abundant protein removal, iTRAQ labeling and nanoLC–MALDI-TOF/TOF-MS analysis was less than 17.5%.
Keywords: Cerebrospinal fluid (CSF); Mass spectrometry (MS); Proteomics; Immunoaffinity subtraction; Protein fractionation; iTRAQ quantification;

A novel molecularly imprinted polymer that could be applied as enrichment sorbent was prepared using methimazole (MMZ) as the template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linker. Though evaluated by static, kinetic and competitive adsorption tests, the polymer exhibited high adsorption capacity, fast kinetics and good selective ability. A method for determination of trace MMZ was developed using this polymer as enrichment sorbent coupled with high performance liquid chromatography focusing on complex biological matrices. Under the optimum experimental conditions, the MMZ standard is linear within the concentration range studied, that is, from 0.5 μg L−1 to 150 μg L−1 (r 2  = 0.9941). Lower limits of detection (LOD, at S/N = 3) and quantification (LOQ, at S/N = 10) in pig samples were 0.63 μg kg−1 and 2.10 μg kg−1 for kidney, 0.51 μg kg−1 and 1.70 μg kg−1 for liver, 0.56 μg kg−1 and 1.86 μg kg−1 for muscle, respectively. Recoveries and relative standard deviation (RSD, n  = 9) values for precision in the developed method were from 71.14% to 88.41% and from 2.53% to 6.18%.
Keywords: Methimazole; Molecularly imprinted polymer; Solid-phase extraction; High performance liquid chromatography;

Analytical procedure for the determination of eprinomectin in soil and cattle faeces by V.D. Litskas; G.C. Batzias; X.N. Karamanlis; A.P. Kamarianos (1537-1542).
A new analytical HPLC-fluorescence method was developed for the quantitative determination of eprinomectin (EPM) in soil and cattle faeces. EPM was extracted with acetone and acetonitrile from soil and cattle faeces, respectively. Solid phase extraction and derivatization reaction with N-methylimidazole in the presence of trifluoroacetic anhydride and acetic acid were applied. The limit of quantitation was 1 ng g−1 air dried soil and 2.5 ng g−1 moist cattle faeces. Overall recovery (RSD) was 89% (8) in soil and 85% (10) in cattle faeces and its good reproducibility (RSD < 15%) allows the application of the method in advanced ecotoxicological studies, required for the environmental fate assessment of EPM.
Keywords: HPLC; Eprinomectin; Avermectins; Soil; Cattle faeces;

Interactions between a model protein (bovine serum albumin—BSA) and the cationic polyelectrolyte, chitosan (Chi), have been characterized by turbidimetry, circular dichroism and fluorescence spectroscopy. It has been found that the conformation of the BSA does not change significantly during the chain interaction between BSA and chitosan forming the non-covalently linked complex. The effects of pH, ionic strength and anions which modify the water structure around BSA were evaluated in the chitosan–BSA complex formation. A net coulombic interaction force between BSA and Chi was found as the insoluble complex formation decreased after the addition of NaCl. Around 80% of the BSA in solution precipitates with the Chi addition. A concentration of 0.05% (w/v) Chi was necessary to precipitate the protein, with a stoichiometry of 6.9 g BSA/g Chi. No modification of the tertiary and secondary structure of BSA was observed when the precipitate was dissolved by changing the pH of the medium. Chitosan proved to be a useful framework to isolate proteins with a slightly acid isoelectrical pH by means of precipitation.
Keywords: Albumin; Chitosan; Polyelectrolyte;

An ammonium sulphate fraction (20–60%) of bifunctional amylase/protease inhibitor from ragi (Eleusine coracana) was purified by affinity chromatography to give 6.59-fold purity with 81.48% yield. The same ammonium sulphate fraction was also subjected to ion exchange chromatography and was purified 4.28-fold with 75.95% yield. The ion exchange fraction was subjected to gel filtration and the inhibitor was purified to 6.67-fold with 67.36% yield. Further sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed to check the homogeneity of purified amylase/trypsin inhibitor obtained through affinity, ion exchange and gel chromatography. The molecular weight of the inhibitor was found to be 14 kDa. This purified inhibitor was used as affinity ligand for the purification of a commercial preparation of pancreatic amylase.
Keywords: Bifunctional amylase/protease inhibitor; Affinity chromatography; Ion exchange chromatography; Gel filtration; Sodium dodecyl sulphate-polyacrylamide gel electrophoresis;

Simultaneous measurement of pazufloxacin, ciprofloxacin, and levofloxacin in human serum by high-performance liquid chromatography with fluorescence detection by Satoshi Watabe; Yoshiaki Yokoyama; Kazuyuki Nakazawa; Kimikazu Shinozaki; Rika Hiraoka; Kei Takeshita; Yukio Suzuki (1555-1561).
In this study, three fluoroquinolones, pazufloxacin, ciprofloxacin and levofloxacin, were simultaneously determined in spiked human serum by high-performance liquid chromatography (HPLC) method with fluorescence detection. Chromatography was performed using a C8 column with an isocratic mobile phase consisting of 1% triethylamine (pH 3.0)/acetonitrile (86/14, v/v). Protein precipitation was conducted using perchloric acid and methanol. The calibration curves for the three fluoroquinolones were linear over concentrations ranging from 0.1 to 20.0 μg/mL. The within-day and between-day coefficients of variation obtained from three fluoroquinolones were less than 7%, and relative errors ranged from −1.6% to 9.3%. Mean recoveries of pazufloxacin, ciprofloxacin, and levofloxacin from spiked human serum were 97%, 88%, and 90%, respectively. The proposed method proved to be simple and reliable for the determination of three fluoroquinolones.
Keywords: Pazufloxacin; Ciprofloxacin; Levofloxacin; HPLC; Validation; Serum;

The purpose of this study was to develop and validate an ultra performance liquid chromatography–mass spectrometry (UPLC/MS) method to investigate the hepatic oxidative metabolism of 2,2′,4,4′,5-pentabromodiphenyl ether (BDE-99), a widely used flame retardant and ubiquitous environmental contaminant. Hydroxylated metabolites were extracted using liquid-to-liquid extraction, resolved on a C18 column with gradient elution and detected by mass spectrometry in single ion recording mode using electrospray negative ionization. The assay was validated for linearity, accuracy, precision, limit of quantification, range and recovery. Calibration curves were linear (R 2  ≥ 0.98) over a concentration range of 0.010–1.0 μM for 4-OH-2,2′,3,4′,5-pentabromodiphenyl ether (4-OH-BDE-90), 5′-OH-2,2′,4,4′,5-pentabromodiphenyl ether (5′-OH-BDE-99) and 6′-OH-2,2′,4,4′,5-pentabromodiphenyl ether (6′-OH-BDE-99), and a concentration range of 0.0625–12.5 μM for 2,4,5-tribromophenol (2,4,5-TBP). Inter- and intra-day accuracy values ranged from −2.0% to 6.0% and from −7.7% to 7.3%, respectively, and inter- and intra-day precision values ranged from 2.0% to 8.5% and from 2.2% to 8.6% (n  = 6), respectively. The limits of quantification were 0.010 μM for 4-OH-BDE-90, 5′-OH-BDE-99 and 6′-OH-BDE-99, and 0.0625 μM for 2,4,5-TBP. Recovery values ranged between 85 and 100% for the four analytes. The validated analytical method was applied to identify and quantify hydroxy BDE-99 metabolites formed in vitro. Incubation of BDE-99 with rat liver microsomes yielded 4-OH-BDE-90 and 6′-OH-BDE-99 as major metabolites and 5′-OH-BDE-99 and 2,4,5-TBP as minor metabolites. To our knowledge, this is the first validated UPLC/MS method to quantify hydroxylated metabolites of PBDEs without the need of derivatization.
Keywords: BDE-99; Rat liver microsomes; Hydroxy metabolites; Ultra performance liquid chromatography–mass spectrometry (UPLC/MS);

Knowledge of the complexation process of oxyresveratrol with β-cyclodextrin (β-CD) under different physicochemical conditions is essential if this potent antioxidant compound is to be used successfully in both food and pharmaceutical industries as ingredient of functional foods or nutraceuticals, despite its poor stability and bioavailability. In this paper, the complexation of oxyresveratrol with natural CDs was investigated for first time using RP-HPLC and mobile phases to which α-, β-, and γ-CD were added. Among natural CDs, the interaction of oxyresveratrol with β-CD was more efficient than with α- and γ-CD. The decrease in the retention times with increasing concentrations of β-CD (0–4 mM) showed that the formation constants (K F ) of the oxyresveratrol/β-CD complexes were strongly dependent on both the water–methanol proportion and the temperature of the mobile phase employed. However, oxyresveratrol formed complexes with β-CD with a 1:1 stoichiometry in all the physicochemical conditions tested. Moreover, to obtain information about the mechanism of the oxyresveratrol affinity for β-CD, the thermodynamic parameters ΔG°, ΔH° and ΔS° were obtained. Finally, to gain information on the effect of the structure of different compounds belonging to the stilbenoids family on the K F values, the complexation of other molecules, resveratrol, pterostilbene and pinosylvin, was studied and compared with the results obtained for the oxyresveratrol/β-CD complexes.
Keywords: Oxyresveratrol; Stilbene; Cyclodextrins; Nanoencapsulation; Reversed-phase liquid chromatography;

The aim of the present work is to apply a non-invasive test, using thumb fingerprint residue analysis, for detection of beta-thalassemia (β-Thal). The relative percentages of free amino acids (AA) in the latent fingerprint of β-Thal patients and healthy subjects were compared. The sample included 24 β-Thal patient and 24 healthy subjects, aged 5–10 years old. Twenty-three AA plus ammonia were analyzed by a sensitive high-performance liquid chromatographic method with fluorescence detection. The profile of AA was calculated based on the percentage of relative amount of each AA to serine (Ser) as it found to be the predominant peak. The statistical and chromatographic profiles of β-Thal patients were characterized by significant decrease of ornithine, lysine, and zero tyrosine, with significant increase of ammonia, and proline. Other amino acids that exist in low ratios were estimated statistically for significance changes. The relative percentages of each AA of healthy subjects were approximately constant. For this reason, these mentioned AA were assigned as major fingerprint markers of β-Thal.
Keywords: Amino acids; Thalassemia; Fingerprint; Marker; Dansyl chloride; HPLC; Fluorescence;

BMS-754807 and metformin were co-administered in drug discovery studies which required the quantitation of both compounds in plasma. Since the two compounds are chemically and structurally dissimilar, developing a single bioanalytical method presented a number of chromatographic challenges including the achievement of appropriate retention times and peak shapes on a single analytical column. To address this chromatographic challenge, we investigated different LC columns under different gradient elution schemes using aqueous/organic mobile phases. Using unbonded silica column and aqueous/methanol mobile phase, we were able to obtain robust and well-resolving chromatographic conditions to support the development and implementation of a single LC–MS/MS bioanalytical method. The use of sub-2 micron particle sizes and a high flow rate, which are attainable with UPLC systems, enhanced the method. The method performance evaluation showed that the method easily met the normally used acceptance criteria for bioanalytical methods, namely a deviation of ±15% from the nominal concentration except at lower limit of quantitation (LLOQ), where ±20% is accepted. The reported LLOQ of 7.8 ng/ml, for both BMS-754807 and metformin, was adequate to support the pharmacokinetic studies.
Keywords: HILIC; LC–MS/MS; UPLC;

Sulfonylurea drugs are often prescribed as a treatment for type II diabetes to help lower blood sugar levels by stimulating insulin secretion. These drugs are believed to primarily bind in blood to human serum albumin (HSA). This study used high-performance affinity chromatography (HPAC) to examine the binding of sulfonylureas to HSA. Frontal analysis with an immobilized HSA column was used to determine the association equilibrium constants (K a ) and number of binding sites on HSA for the sulfonylurea drugs acetohexamide and tolbutamide. The results from frontal analysis indicated HSA had a group of relatively high-affinity binding regions and weaker binding sites for each drug, with average K a values of 1.3 (±0.2) × 105 and 3.5 (±3.0) × 102  M−1 for acetohexamide and values of 8.7 (±0.6) × 104 and 8.1 (±1.7) × 103  M−1 for tolbutamide. Zonal elution and competition studies with site-specific probes were used to further examine the relatively high-affinity interactions of these drugs by looking directly at the interactions that were occurring at Sudlow sites I and II of HSA (i.e., the major drug-binding sites on this protein). It was found that acetohexamide was able to bind at both Sudlow sites I and II, with K a values of 1.3 (±0.1) × 105 and 4.3 (±0.3) × 104  M−1, respectively, at 37 °C. Tolbutamide also appeared to interact with both Sudlow sites I and II, with K a values of 5.5 (±0.2) × 104 and 5.3 (±0.2) × 104  M−1, respectively. The results provide a more quantitative picture of how these drugs bind with HSA and illustrate how HPAC and related tools can be used to examine relatively complex drug–protein interactions.
Keywords: Sulfonylurea drugs; Acetohexamide; Tolbutamide; Human serum albumin; High-performance affinity chromatography; Frontal analysis; Zonal elution; Competition studies; Drug–protein binding;

A simple method of hollow fiber-liquid phase microextraction (HF-LPME) combined with gas chromatography (GC) was developed for the analysis of four phenothiazine drugs (promethazine, promazine, chlorpromazine and trifluoperazine) in human urine samples. All variables affecting the extraction of target analytes including organic solvent type, stirring rate, extraction time, extraction temperature, pH of sample solution and ionic strength were carefully studied and optimized. Under the optimal conditions, the analytical performance of HF-LPME-GC-flame photometric detector (FPD) and HF-LPME-GC-flame ionization detector (FID) were evaluated and compared. The results showed that the HF-LPME-GC-FID was more sensitive than HF-LPME-GC-FPD for the determination of four target phenothiazine drugs, while the signal peak shape and resolution obtained by HF-LPME-GC-FPD was better than that obtained by HF-LPME-GC-FID. HF-LPME-GC-FPD/FID was successfully applied for the assay of the interested phenothiazine drugs in urine sample, and the excretion of the drugs was also investigated by monitoring the variation of the concentration of chlorpromazine in urine of a psychopath within 8 h after drug-taking. The proposed method provided an effective and fast way for the therapeutic drug monitoring (TDM) of phenothiazine.
Keywords: Hollow fiber-liquid phase microextraction; Phenothiazine drugs; Urine; Gas chromatography;

A simple, rapid, sensitive and specific ultra performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS) method was developed and validated for the quantification of ethosuximide in human plasma is described. Analyte was chromatographed on a Hypersil Gold C18 column (100 mm × 2.1 mm, i.d., 1.9 μm) with isocratic elution at a flow rate of 0.250 mL/min and pravastatin was used as the internal standard. The assay involves a simple solid-phase extraction procedure of 0.25 mL human plasma and the analysis was performed on a triple-quadrupole tandem mass spectrometer by MRM mode via electrospray ionization (ESI). The method was linear in the concentration range of 0.25–60.0 μg/mL. The lower limit of quantification (LLOQ) was 0.25 μg/mL. The within- and between-day precision and accuracy of the quality control samples were within 10.0%. The recovery was 95.1% and 94.4% for ethosuximide and pravastatin, respectively. The analysis time for each sample was 1.8 min. The method was highly reproducible and gave peaks with excellent chromatography properties.
Keywords: Ethosuximide; LC–MS/MS; Human plasma; Acquity UPLC;

A sensitive, simple and rapid ultra fast liquid chromatography (UFLC)–ESI-MS/MS method was developed for the determination of 2-hydroxyflutamide in human plasma using tegafur as the internal standard. The plasma sample was pretreated with methanol for protein precipitation and the analytes were separated on an Ultimate C18 column (5 μm, 2.1 mm × 50 mm, MD, USA) with the mobile phase consisted of acetonitrile and water (2:1, v/v). Detection was performed on a triple-quadrupole tandem mass spectrometer under a negative multiple reaction-monitoring mode (MRM). The mass transition ion-pair was followed as m/z 290.90–204.8 for 2-hydroxyflutamide and 198.9–128.8 for tegafur. Linear calibration curves were obtained in the concentration range of 1.742–1452 ng/ml with a lower limit of quantification of 1.742 ng/ml. The intra- and inter-batch precision values were less than 8.1% and 5.6%, respectively. The established method was successfully applied to a bioequivalence study of two flutamide preparations (250 mg) in 20 healthy male volunteers.
Keywords: 2-Hydroxyflutamide; LC–MS/MS; Bioequivalence;

Analysis of amphetamines and metabolites in urine with ultra performance liquid chromatography tandem mass spectrometry by María del Mar Ramírez Fernández; Sarah M.R. Wille; Vincent di Fazio; Matthias Gosselin; Nele Samyn (1616-1622).
A simple, rapid and sensitive ultra performance liquid chromatography tandem mass spectrometry method was developed and fully validated for the quantitative determination of seven amphetamines and metabolites in urine. The method was validated for selectivity, linearity, LOQ, LOD, imprecision, bias, analyte and processed sample stability, matrix effect, recovery, carryover and dilution integrity. A classic liquid–liquid extraction with ethyl acetate was used as sample preparation procedure. The compounds were separated on an Acquity UPLC HSS C18 column in 6.8 min. The linear dynamic range was established from 25 to 500 ng/mL. The limit of quantification was fixed to the lowest calibrator level and the limit of detection ranged from 0.125 to 2.5 ng/mL. The method presented an excellent intra- and inter-assay imprecision and bias (<10.7%) at each measured concentration of two external quality controls (QC) and three “in house” QC. No matrix effects were observed and good recoveries (>70%) were obtained for all the compounds. No carryover was observed after the analysis of high concentrated samples (8000 ng/mL). The method was subsequently applied to authentic samples.
Keywords: UPLC–MS/MS; Urine; Amphetamines;

A sensitive and high throughput off-line μElution 96-well solid-phase extraction (SPE) followed by strong cation exchange (SCX) liquid chromatography with tandem mass spectrometry (LC/MS/MS) quantification for determination of cefepime has been developed and validated in mouse plasma. Using the chemical analog, ceftazidime as an internal standard (IS), the linear range of the method for the determination of cefepime in mouse plasma was 4–2048 ng/mL with the lower limit of quantitation level (LLOQ) of 4 ng/mL. The inter- and intra-assay precision and accuracy of the method were below 9.05% and ranged from 95.6 to 113%, respectively, determined by quality control (QC) samples at five concentration levels including LLOQ. After μElution SPE, 71.1% of cefepime was recovered. The application of the validated assay for the determination of cefepime in mouse pharmacokinetics (PK) samples after intravenous (IV) and subcutaneous (SC) doses was demonstrated.
Keywords: Cefepime; μElution SPE; SCX; LC/MS/MS; Mouse plasma; Pharmacokinetics;

Midazolam is an ultra short acting benzodiazepine derivative and a specific probe for phenotyping cytochrome P450 (P450) 3A4/5 activity. A rapid, sensitive, and selective LC–MS/MS method was developed for simultaneous quantitation of midazolam and its metabolites (1′-hydroxymidazolam and 4-hydroxymidazolam). Deuterated (D5) analog of midazolam was utilized as an internal standard. Sample preparation either from human plasma (100 μL) or liver microsomal incubations involved a simple protein precipitation using acetonitrile (900 μL) with an average recovery of >90% for all compounds. The chromatographic separation was achieved using Zorbax-SB Phenyl, Rapid Resolution HT (2.1 mm × 100 mm, 3.5 μm) and a gradient elution with 10 mM ammonium acetate in 10% methanol (A) and acetonitrile (B). The flow rate was 0.25 mL/min and total run time was 5.5 min. Calibration curves were linear over the concentration range of 0.100–250 ng/mL. The lower limit of quantitation (LLOQ) was 0.1 ng/mL for all three analytes. The accuracy and precision, estimated at LLOQ and three concentration levels of quality control samples in six replicates, were within 85–115%. In conclusion, a robust, simple and highly sensitive analytical method was developed and validated for the analysis of midazolam and its metabolites. This method is suitable for characterizing the P450 3A4/5 activity in vitro or in human pharmacokinetic studies allowing administration of smaller doses of midazolam.
Keywords: 1′-hydroxymidazolam; 4-hydroxymidazolam; Midazolam; Cytochrome P450 3A; Phenotyping; LC–MS/MS;

Accurate analysis of urea in milk and milk powder by isotope dilution gas chromatography–mass spectrometry by Xinhua Dai; Xiang Fang; Fuhai Su; Mengrui Yang; Hongmei Li; Jian Zhou; Ruifeng Xu (1634-1638).
A high order method for measuring urea concentrations in milk and milk powder was developed. The method can be applied to certify the concentration of urea in some new milk and milk powder CRMs. This high accurate method for analysis of milk is valuable given the inherent challenges associated with the complexity of the sample matrix. A measurement procedure based on gas chromatography/isotope dilution mass spectrometry (GC/IDMS) was developed. Samples were pre-treated with acetonitrile to remove proteins and the method was applied to determine urea concentrations in milk and milk powder. Excellent precision was obtained, with within- and between-set coefficients of variation of 0.15–0.46 and 0.18–0.65%, respectively. The measurement uncertainty is evaluated. The method can trace to mass.
Keywords: Milk; Milk powder; Isotope dilution; Gas chromatography–mass spectrometry; Urea;

The unmitigated rise in demand for the assessment of vitamin D status has taxed the ability of clinical mass spectrometry laboratories to preserve turn-around times. We aimed to improve the throughput of liquid–liquid extraction of plasma/serum for the assay of 25-hydroxy vitamin D.We designed and fabricated a flexible rubber gasket that seals two 96-well plates together to quantitatively transfer the contents of one plate to another. Using the transfer gasket and a dry-ice acetone bath to freeze the aqueous infranatant, we developed a novel liquid–liquid extraction workflow in a 96-well plate format. We applied the technology to the mass spectrometric quantification of 25-hydroxy vitamin D.Cross-contamination between wells was ≤0.13%. The interassay imprecision over 132 days of clinical implementation was less than 10%. The method compared favorably to a standard liquid–liquid extraction in glass tubes (Deming slope = 1.018, S x|y  = 0.022). The accuracy of the assay was 102–105% as assessed with the recently released control materials from NIST.The development of a plate-sealing gasket permits the liquid–liquid extraction of clinical specimens in a moderate-throughput workflow and the reliable assay of vitamin D status. In the future, the gasket may also prove useful in other sample preparation techniques for HPLC or mass spectrometry.
Keywords: Vitamin D; Liquid chromatography–tandem mass spectrometry; Assay; 96-well plate; Liquid–liquid extraction;

A rapid, simple and sensitive method was developed for the determination of para-aminohippuric acid (PAH) in rat plasma using liquid chromatography tandem mass spectrometry (LC-MS-MS). Acetaminophen was used as the internal standard. Chromatographic separation was performed using a Symmetry C18 column and the mobile phase was composed of A: 2 mM ammonium formate and 0.1% formic acid in water and B: 2 mM ammonium formate and 0.1% formic acid in acetonitrile (ACN) (A:B, 30:70, v/v). Detection was performed on a triple–quadrupole tandem mass spectrometer using positive ion mode electrospray ionization (ESI) in the multiple reaction monitoring (MRM) mode. The MS/MS ion transitions monitored were m/z 195.2 → 120.2 and 152.1 → 110.1 for PAH and acetaminophen, respectively. Good linearity is observed over the concentration range of 0.1–500 μg/ml. The method was proved to be accurate and reliable and was applied to a pharmacokinetic study in rat.
Keywords: Para-aminohippuric acid; Liquid chromatography-tandem mass spectrometry; Pharmacokinetics; Analytical validation; Acetaminophen; Rat plasma;

Preparative separation of alkaloids from Nelumbo nucifera leaves by conventional and pH-zone-refining counter-current chromatography by Zheng Zhenjia; Wang Minglin; Wang Daijie; Duan Wenjuan; Wang Xiao; Zheng Chengchao (1647-1651).
Two modes of high-speed counter-current chromatography (HSCCC) were successfully applied to the separation of alkaloids from crude extract of Nelumbo nucifera leaves. The conventional HSCCC separations were performed with a two-phase solvent system composed of tetrachloromethane–CHCl3–methanol–0.1 M HCl at a volume ratio of 1:3:3:2 (v/v/v/v), and 120 mg crude extract could be successfully separated. pH-Zone-refining CCC was performed with a two-phase solvent system composed of petroleum ether (60–90 °C)–ethyl acetate–methanol–water (5:5:2:8, v/v/v/v) where triethylamine (10 mM) was added to the upper organic stationary phase as a retainer and hydrochloric acid (5 mM) to the aqueous mobile phase as an eluent. From 4.0 g of the crude extract, 120 mg N-nornuciferine, 1020 mg nuciferine and 96 mg roemerine were obtained in a single run each with a purity of over 98% as determined by HPLC. The structures of the isolated compounds were identified by ESI-MS, 1H NMR and 13C NMR.
Keywords: Nelumbo nucifera; Counter-current chromatography; Preparative chromatography; N-nornuciferine; Nuciferine; Roemerine;