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Ionization Mode (ionization + mode)
Kinds of Ionization Mode Selected AbstractsCEC-ESI ion trap MS of multiple drugs of abuseELECTROPHORESIS, Issue 7 2010Zeineb Aturki Abstract This article describes a method for the separation and determination of nine drugs of abuse in human urine, including amphetamines, cocaine, codeine, heroin and morphine. This method was based on SPE on a strong cation exchange cartridge followed by CEC-MS. The CEC experiments were performed in fused silica capillaries (100,,m×30,cm) packed with a 3,,m cyano derivatized silica stationary phase. A laboratory-made liquid junction interface was used for CEC-MS coupling. The outlet capillary column was connected with an emitter tip that was positioned in front of the MS orifice. A stable electrospray was produced at nanoliter per minute flow rates applying a hydrostatic pressure (few kPa) to the interface. The coupling of packed CEC columns with mass spectrometer as detector, using a liquid junction interface, provided several advantages such as better sensitivity, low dead volume and independent control of the conditions used for CEC separation and ESI analysis. For this purpose, preliminary experiments were carried out in CEC-UV to optimize the proper mobile phase for CEC analysis. Good separation efficiency was achieved for almost all compounds, using a mixture containing ACN and 25,mM ammonium formate buffer at pH 3 (30:70, v/v), as mobile phase and applying a voltage of 12,kV. ESI ion-trap MS detection was performed in the positive ionization mode. A spray liquid, composed by methanol,water (80:20, v/v) and 1% formic acid, was delivered at a nano-flow rate of ,200,nL/min. Under optimized CEC-ESI-MS conditions, separation of the investigated drugs was performed within 13,min. CEC-MS and CEC-MS2 spectra were obtained by providing the unambiguous confirmation of these drugs in urine samples. Method precision was determined with RSDs values ,3.3% for retention times and ,16.3% for peak areas in both intra-day and day-to-day experiments. LODs were established between 0.78 and 3.12,ng/mL for all compounds. Linearity was satisfactory in the concentration range of interest for all compounds (r2,0.995). The developed CEC-MS method was then applied to the analysis of drugs of abuse in spiked urine samples, obtaining recovery data in the range 80,95%. [source] Analyses of alkaloids in different products by NACE-MSELECTROPHORESIS, Issue 22 2007Chen-Wen Chiu Abstract A simple method for the separation and characterization of five nicotine-related alkaloids by NACE employing UV and MS detections is described here for the first time. Several factors, including NACE parameters (compositions of running solution) and MS parameters (such as nature and flow rate of sheath liquid, pressure of nebulization gas, and flow rate of dry gas), were optimized in order to obtain both an adequate CE separation and high MS signals for the alkaloid compounds used in this study. A reliable CE separation of five alkaloids was achieved in 50,mM ammonium formate that was dissolved in an ACN/methanol mixture (50:50, v/v) of pH*,4.0 (apparent pH 4.0). The optimal electrospray MS measurement was carried out in the positive ionization mode using a coaxial sheath liquid composed of isopropyl alcohol and water in the ratio of 80:20 v/v at a flow rate of 180,,L/h. In addition, the proposed NACE method was also applied in the analyses of alkaloids in several products including chewing gums, beverages, and tobaccos. This NACE-MS method was found to provide a better detection ability and separation resolution for the analysis of nicotine alkaloids when compared to other aqueous CE-MS reports. [source] Optimization of the ESI and APCI experimental variables for the LC/MS determination of s-triazines, methylcarbamates, organophosphorous, benzimidazoles, carboxamide and phenylurea compounds in orange samplesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2007Guilherme M. Titato Abstract In this work, ten selected pesticides of different chemical groups, indicated to orange culture, were extracted and determined by liquid chromatography,mass spectrometry using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) operating in the positive ion detection mode. Applying a variables selection technique verified that cone voltage, source temperature and drying-gas flow-rate are the critical variables when the ESI was used, while cone voltage was found to be the only critical variable for the MS system, operating with the APCI ionization mode. After optimization of the most important parameters through the variables selection technique, the selected ion-recording (SIR) mode, monitoring the [M + H]+ species for all the compounds, was applied for the method validation of the pesticides, in both ionization modes. In orange samples, matrix effects did not interfere with the determination of the pesticides. Pesticides quantification limits ranged from 10 to 50 µg kg,1 for ESI and from 8.2 to 45 µg kg,1 for APCI. Linearity was studied from LOQ upto 200 times LOQ values (r > 0.98). Recoveries obtained were in the range of 70.2,100.5% (RSDs less than 10%). In order to guarantee that the identification and confirmation of the studied pesticides in real samples were unequivocal, characteristic fragment ions of the pesticides were obtained by varying the cone voltage (in-source CID). Copyright © 2007 John Wiley & Sons, Ltd. [source] Determination of clavulanic acid in calf plasma by liquid chromatography tandem mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 11 2006Tim Reyns Abstract A method for the quantification of clavulanic acid in calf plasma using high-performance liquid chromatography combined with electrospray ionization (ESI) mass spectrometry, operating in the negative ionization mode (LC-MS/MS), is presented. Sample preparation includes a simple and fast deproteinization with acetonitrile and a back-extraction of the acetonitrile with dichloromethane. Chromatography is performed on a reversed-phase PLRP-S polymeric column using 0.05% formic acid in water and acetonitrile. The limit of quantification is 25 ng/ml, which is lower than other published methods using ultraviolet (UV), fluorimetric or mass spectrometric detection. The limit of detection is calculated to be 3.5 ng/ml. The stability of clavulanic acid was demonstrated according to The Guidelines of Bioanalytical Method Validation of The Food and Drug Administration (FDA): freeze and thaw stability, short-term stability, long-term stability, stock solution stability and postpreparative stability. The method is used in a pharmacokinetic and bioequivalence study of amoxycillin/clavulanic acid formulations in calves. Copyright © 2006 John Wiley & Sons, Ltd. [source] Development and validation of a liquid chromatographic/tandem mass spectrometric assay for the quantitation of nucleoside HIV reverse transcriptase inhibitors in biological matricesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2005Séverine Compain Abstract Besides liquid chromatographic (LC)/UV methods adapted to therapeutic drug monitoring, there is still a need for more powerful techniques that can be used for pharmacological research and clinical purposes. We developed an LC method coupled with tandem mass spectrometry (MS/MS) to separate, detect and quantify with high sensitivity the nucleoside analogues used in multitherapies (zidovudine, stavudine, zalcitabine, didanosine, lamivudine and abacavir) in plasma and in the intracellular medium. We worked on two essential issues: (i) the need to use two ionization modes in order to achieve the best sensitivity, which leads to the optimization of the chromatographic separation of drugs detected in the positive ionization mode and drugs detected in the negative ionization mode, and (ii) the need to optimize the extraction step in order to enhance sample recovery. The peripheral blood mononuclear cells were lysed in Tris buffer,MeOH. A clean-up procedure was performed by solid-phase extraction only for plasma samples. The LC separation was carried out on a Zorbax Stable Bond C18 column followed by MS/MS analysis after electrospray ionization in either the negative or positive mode. The positive ionization mode was applied at the beginning of the run to detect zalcitabine and lamivudine, then the ionization mode was changed to negative for the detection of didanosine, stavudine, internal standard and zidovudine. The calibration range for all the analytes was 0.5,200 ng ml,1. The recoveries were between 64 and 90%, with coefficients of variation (CVs) lower than 15%. The inaccuracy (bias) was ±15% with CVs always lower than 12%. The analytes were stable at room temperature and in the extraction solvent for at least 24 h, after storage at ,80 °C for 3 months, after three freeze,thaw cycles and in the injection solvent after 48 h at 4 °C. Together with the measurement of intracellular triphosphorylated metabolites thanks to the powerful plasma and intracellular assay method for intact drugs, it is possible to describe the behaviour of nucleoside analogues against HIV through plasma pharmacokinetics, cell membrane diffusion including drug transport involvement, and also the intracellular metabolism. Copyright © 2005 John Wiley & Sons, Ltd. [source] Exact mass measurement on an electrospray ionization time-of-flight mass spectrometer: error distribution and selective averagingJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2003Jiejun Wu Abstract An automated, accurate and reliable way of acquiring and processing flow injection data for exact mass measurement using a bench-top electrospray ionization time-of-flight (ESI-TOF) mass spectrometer is described. Using Visual Basic programs, individual scans were selected objectively with restrictions on ion counts per second for both the compound of interest and the mass reference peaks. The selected ,good scans' were then subjected to two different data-processing schemes (,combine-then-center' and ,center-then-average'), and the results were compared at various ion count limit settings. It was found that, in general, the average of mass values from individual scans is more accurate than the centroid mass value of the combined (same) scans. In order to acquire a large number of good scans in one injection (to increase the sampling size for statistically valid averaging), an on-line dilution chamber was added to slow down the typically rapid mass chromatographic peak decay in flow-injection analysis. This simple addition worked well in automation without the need for manual sample dilution. In addition, by dissolving the reference compound directly into the mobile phase, manual syringe filling can be eliminated. Twenty-seven samples were analyzed with the new acquisition and process routines in positive electrospray ionization mode. For the best method found, the percentage of samples with RMS error less than 5 ppm was 100% with repetitive injection data (6 injections per sample), and 95% with single injection data. Afterwards, 31 other test samples were run (with MW ranging from 310 to 3493 Da, 21 samples in ESI+ and 10 in ESI, mode) and processed with similar parameters and 100% of them were mass-calculated to RMS error less than 5 ppm also. Copyright © 2003 John Wiley & Sons, Ltd. [source] Determination of eight fatty acid ethyl esters in meconium samples by headspace solid-phase microextraction and gas chromatography,mass spectrometryJOURNAL OF SEPARATION SCIENCE, JSS, Issue 14 2010Marli Roehsig Abstract A number of fatty acid ethyl esters (FAEEs) have recently been detected in meconium samples. Several of these FAEEs have been evaluated as possible biomarkers for in utero ethanol exposure. In the present study, a method was optimized and validated for the simultaneous determination of eight FAEEs (ethyl laurate, ethyl myristate, ethyl palmitate, ethyl palmitoleate, ethyl stearate, ethyl oleate, ethyl linoleate and ethyl arachidonate) in meconium samples. FAEEs were extracted by headspace solid-phase microextraction. Analyte detection and quantification were carried out using GC-MS operated in chemical ionization mode. The corresponding D5-ethyl esters were synthesized and used as internal standards. The LOQ and LOD for each analyte were <150 and <100,ng/g, respectively. The method showed good linearity (r2>0.98) in the concentration range studied (LOQ , 2000,ng/g). The intra- and interday imprecision, given by the RSD of the method, was lower than 15% for all FAEEs studied. The validated method was applied to 63 authentic specimens. FAEEs could be detected in alcohol-exposed newborns (>600,ng/g cumulative concentration). Interestingly, FAEEs could also be detected in some non-exposed newborns, although the concentrations were much lower than those measured in exposed cases. [source] Direct characterization of aqueous extract of Hibiscus sabdariffa using HPLC with diode array detection coupled to ESI and ion trap MSJOURNAL OF SEPARATION SCIENCE, JSS, Issue 20 2009Inmaculada C. Rodríguez-Medina Abstract The phenolic fraction and other polar compounds of the Hibiscus sabdariffa were separated and identified by HPLC with diode array detection coupled to electrospray TOF and IT tandem MS (DAD-HPLC-ESI-TOF-MS and IT-MS). The H. sabdariffa aqueous extract was filtered and directly injected into the LC system. The analysis of the compounds was carried out by RP HPLC coupled to DAD and TOF-MS in order to obtain molecular formula and exact mass. Posterior analyses with IT-MS were performed and the fragmentation pattern and confirmation of the structures were achieved. The H. sabdariffa samples were successfully analyzed in positive and negative ionization modes with two optimized linear gradients. In positive mode, the two most representative anthocyanins and other compounds were identified whereas the phenolic fraction, hydroxycitric acid and its lactone were identified using the negative ionization mode. [source] High sensitivity determination of valproic acid in mouse plasma using semi-automated sample preparation and liquid chromatography with tandem mass spectrometric detectionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2005Vincenzo Pucci A high-throughput liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) assay using automated sample preparation has been developed for the determination of valproic acid (VPA) in mouse plasma. A liquid-handling system was programmed to prepare calibration standard solutions in plasma, as well as quality controls and clinical samples. Plasma protein precipitation was performed on a 96-well plate, and the collected supernatant was directly injected into a reversed-phase LC/ESI-MS/MS system in the negative ionization mode. The calibration curve for VPA was linear over a dynamic range of 0.15,100,µg/mL. The limit of detection was 75,ng/mL and the lower limit of quantitation was 150,ng/mL. Intra- and inter-day validation assays of the semi-automated plasma analysis showed satisfactory accuracy and precision. Copyright © 2005 John Wiley & Sons, Ltd. [source] Simultaneous determination of lamivudine, stavudine and nevirapine in human plasma by LC,MS/MS and its application to pharmacokinetic study in clinicBIOMEDICAL CHROMATOGRAPHY, Issue 9 2010Zhou Li Abstract A new high-throughput LC,MS/MS method for the simultaneous determination of lamivudine (3TC), stavudine (d4T) and nevirapine (NVP) in human plasma is presented, with zidovudine as an internal standard. The analytes were extracted from plasma by protein precipitation and only 150,,L plasma was needed. Chromatographic separation was achieved on a Shiseido C8 column (150 × 2.0,mm, 5,,m) with a total run time of 6,min. A tandem mass spectrometric detection was conducted using multiple reaction monitoring under positive ionization mode with an electrospray ionization interface. The method was developed and validated over the concentration range of 25,5000,ng/mL for 3TC and NVP and 20,4000,ng/mL for d4T. The method was validated in terms of intra- and inter-day precision (,8.6%), accuracy (within ± 8.4%), linearity and specificity. The method has been successfully applied to the pharmacokinetic study of a combination treatment of 300,mg lamivudine, 30,mg stavudine and 200,mg nevirapine in 22 healthy male volunteers under fasting conditions. Copyright © 2010 John Wiley & Sons, Ltd. [source] Determination of a novel paclitaxel derivative (NPD-103) in human plasma by ultra-performance liquid chromatography,tandem mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 5 2009Shuang-Qing Zhang Abstract A sensitive and specific ultra-performance liquid chromatography,tandem mass spectrometry (UPLC-MS-MS) method for quantification of a newly developed anticancer agent NPD-103 has been established. An aliquot of human plasma sample (200 µL) was spiked with 13C-labeled paclitaxel (internal standard) and extracted with 1.3 mL of tert -butyl methyl ether. NPD-103 was quantitated on a C18 column with methanol,0.1% formic acid (75:25, v/v) as mobile phase using UPLC-MS-MS operating in positive electrospray ionization mode with a total run time of 3.0 min. For NPD-103 at the concentrations of 1.0, 5.0 and 10.0 µg/mL in human plasma, the absolute extraction recoveries were 95.58, 102.43 and 97.77%, respectively. The linear quantification range of the method was 0.1,20.0 µg/mL in human plasma with linear correlation coefficients greater than 0.999. The intra- and inter-day accuracy for NPD-103 at 1.0, 5.0 and 10.0 µg/mL levels in human plasma fell into the ranges of 95.29,100.00% and 91.04,94.21%, and the intra- and inter-day precisions were in the ranges of 8.96,11.79% and 7.25,10.63%, respectively. This assay is applied to determination of half-life of NPD-103 in human plasma. Copyright © 2008 John Wiley & Sons, Ltd. [source] Determination of a novel epothilone D analog (AV-EPO-106) in human plasma using ultra-performance liquid chromatography,tandem mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 3 2009Shuang-Qing Zhang Abstract A novel ultra-performance liquid chromatography,tandem mass spectrometry (UPLC-MS-MS) method has been established for the determination of a newly synthesized epothilone D analog (AV-EPO-106) in human plasma. The plasma samples were prepared by liquid,liquid extraction with cold tert -butyl methyl ether. The chromatographic separation was achieved within 5 min on a C18 column with water,methanol (10:90, v/v) as mobile phase at a flow-rate of 0.8 mL/min. Mass transition of m/z 568.2 to 386.1 was measured for AV-EPO-106 in positive atmospheric pressure chemical ionization mode. A detailed validation of the method was performed as per the USFDA guidelines. For AV-EPO-106 at the concentrations of 1.0, 5.0 and 10.0 µg/mL in human plasma, the absolute extraction recoveries were 86.17, 85.24 and 85.69%, respectively. The linear quantification range of the method was 0.10,20.0 µg/mL in human plasma with linear correlation coefficients greater than 0.999. The intra-day and inter-day accuracy for AV-EPO-106 at the levels of 1.0, 5.0 and 10.0 µg/mL in human plasma fell in the ranges of 98.25,100.47 and 94.19,97.25%, and the intra- and inter-day precision were in the ranges of 4.75,6.30% and 8.89,10.45%, respectively. The method was successfully applied to quantify AV-EPO-106 in human plasma to determine the half-life of this compound in human plasma. Copyright © 2008 John Wiley & Sons, Ltd. [source] Identification of key metabolites of tectorigenin in rat urine by HPLC-MSnBIOMEDICAL CHROMATOGRAPHY, Issue 2 2009Wei-Dong Zhang Abstract This is a report about the identification of key metabolites of tectorigenin in rat urine using high-performance liquid chromatography,electrospray ionization ion trap tandem mass spectrometric method (HPLC-ESI-MSn). Six healthy rats were administered a single dose (80 mg/kg) of tectorigenin by oral gavage. Urine was sampled for 0,24 h and centrifuged at 12,000 rpm for 10 min to obtain the supernatants, then the supernatants were purified by solid-phase extraction with a C18 cartridge. The chromatographic separation was carried out on a reversed-phase C18 column with a gradient elution program whereas acetonitrile,0.1% formic acid water was used as mobile phase. Mass spectra were acquired in negative ionization mode and a data-dependant scan was used for the identification of the key metabolites of tectorigenin in the urine samples. As a result, four phase II metabolites and the parent drug tectorigenin were found and identified in rat urine for the first time. Copyright © 2008 John Wiley & Sons, Ltd. [source] Assessment of matrix effects and determination of niacin in human plasma using liquid,liquid extraction and liquid chromatography,tandem mass spectrometryBIOMEDICAL CHROMATOGRAPHY, Issue 11 2008Michael C. Peoples Abstract A simple, sensitive and rapid liquid,liquid extraction method for the analysis of nicotinic acid (niacin) and its labeled internal standard nicotinic acid-d4 (niacin-d4) in human plasma was developed and validated. The analyte and its internal standard were isolated from acidified plasma using a single liquid,liquid extraction procedure with methyl- t -butyl ether. The extracted samples were analyzed by liquid chromatography,tandem mass spectrometry in positive electrospray ionization mode with multiple reaction monitoring. The calibration curves were linear in the measured range between 5 and 1000 ng/mL and the limit of detection was calculated as 122 pg/mL. The method required 250 µL of human plasma and the total run time between injections was 3.5 min. Matrix effects were assessed by post-column infusion experiments, phospholipids monitoring and post-extraction addition experiments. The extraction of phospholipids and niacin from plasma was studied under acidic, neutral and basic conditions. Acidic conditions were optimal for both the recovery of niacin and the removal of phospholipids; the degree of matrix effects for niacin was determined to be 2.5%. It was concluded that effective removal of matrix components can overcome low recovery issues associated with liquid,liquid extractions of polar analytes. Copyright © 2008 John Wiley & Sons, Ltd. [source] Analyses of second-generation ,legal highs' in the UK: Initial findingsDRUG TESTING AND ANALYSIS, Issue 8 2010Simon D. Brandt Abstract In the UK, mephedrone and other so-called ,legal high' derivatives have recently been classified as Class B, Schedule I under the Misuse of Drugs Act 1971. Since then, alternative products have been advertised on a number of websites. In order to obtain an immediate snapshot of the situation, 24 products were purchased online from 18 UK-based websites over a period of 6 weeks following the ban in April 2010. Qualitative analyses were carried out by gas chromatography ion trap mass spectrometry using electron- and chemical ionization modes, nuclear magnetic resonance spectroscopy, and comparison with reference standards. Overall, the purchased products consisted of single cathinones or cathinone mixtures including mephedrone, butylone, 4-methyl- N -ethylcathinone, flephedrone (4-fluoromethcathinone) and MDPV (3,4-methylenedioxypyrovalerone), respectively. Benzocaine, caffeine, lidocaine, and procaine were also detected. The emphasis was placed on ,Energy 1' (NRG-1), a product advertised as a legal replacement for mephedrone-type derivatives usually claiming to contain naphyrone (naphthylpyrovalerone, O-2482). It was found that 70% of NRG-1 and NRG-2 products appeared to contain a mixture of cathinones banned in April 2010 and rebranded as ,new' legal highs, rather than legal chemicals such as naphyrone as claimed by the retailers. Only one out of 13 NRG-1 samples appeared to show analytical data consistent with naphyrone. These findings also suggest that both consumers and online sellers (unlike manufacturers and wholesalers) are, most likely unknowingly, confronted with the risk of criminalization and potential harm. Copyright © 2010 John Wiley & Sons, Ltd. [source] Optimization of the ESI and APCI experimental variables for the LC/MS determination of s-triazines, methylcarbamates, organophosphorous, benzimidazoles, carboxamide and phenylurea compounds in orange samplesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2007Guilherme M. Titato Abstract In this work, ten selected pesticides of different chemical groups, indicated to orange culture, were extracted and determined by liquid chromatography,mass spectrometry using both electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) operating in the positive ion detection mode. Applying a variables selection technique verified that cone voltage, source temperature and drying-gas flow-rate are the critical variables when the ESI was used, while cone voltage was found to be the only critical variable for the MS system, operating with the APCI ionization mode. After optimization of the most important parameters through the variables selection technique, the selected ion-recording (SIR) mode, monitoring the [M + H]+ species for all the compounds, was applied for the method validation of the pesticides, in both ionization modes. In orange samples, matrix effects did not interfere with the determination of the pesticides. Pesticides quantification limits ranged from 10 to 50 µg kg,1 for ESI and from 8.2 to 45 µg kg,1 for APCI. Linearity was studied from LOQ upto 200 times LOQ values (r > 0.98). Recoveries obtained were in the range of 70.2,100.5% (RSDs less than 10%). In order to guarantee that the identification and confirmation of the studied pesticides in real samples were unequivocal, characteristic fragment ions of the pesticides were obtained by varying the cone voltage (in-source CID). Copyright © 2007 John Wiley & Sons, Ltd. [source] Development and validation of a liquid chromatographic/tandem mass spectrometric assay for the quantitation of nucleoside HIV reverse transcriptase inhibitors in biological matricesJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2005Séverine Compain Abstract Besides liquid chromatographic (LC)/UV methods adapted to therapeutic drug monitoring, there is still a need for more powerful techniques that can be used for pharmacological research and clinical purposes. We developed an LC method coupled with tandem mass spectrometry (MS/MS) to separate, detect and quantify with high sensitivity the nucleoside analogues used in multitherapies (zidovudine, stavudine, zalcitabine, didanosine, lamivudine and abacavir) in plasma and in the intracellular medium. We worked on two essential issues: (i) the need to use two ionization modes in order to achieve the best sensitivity, which leads to the optimization of the chromatographic separation of drugs detected in the positive ionization mode and drugs detected in the negative ionization mode, and (ii) the need to optimize the extraction step in order to enhance sample recovery. The peripheral blood mononuclear cells were lysed in Tris buffer,MeOH. A clean-up procedure was performed by solid-phase extraction only for plasma samples. The LC separation was carried out on a Zorbax Stable Bond C18 column followed by MS/MS analysis after electrospray ionization in either the negative or positive mode. The positive ionization mode was applied at the beginning of the run to detect zalcitabine and lamivudine, then the ionization mode was changed to negative for the detection of didanosine, stavudine, internal standard and zidovudine. The calibration range for all the analytes was 0.5,200 ng ml,1. The recoveries were between 64 and 90%, with coefficients of variation (CVs) lower than 15%. The inaccuracy (bias) was ±15% with CVs always lower than 12%. The analytes were stable at room temperature and in the extraction solvent for at least 24 h, after storage at ,80 °C for 3 months, after three freeze,thaw cycles and in the injection solvent after 48 h at 4 °C. Together with the measurement of intracellular triphosphorylated metabolites thanks to the powerful plasma and intracellular assay method for intact drugs, it is possible to describe the behaviour of nucleoside analogues against HIV through plasma pharmacokinetics, cell membrane diffusion including drug transport involvement, and also the intracellular metabolism. Copyright © 2005 John Wiley & Sons, Ltd. [source] Direct characterization of aqueous extract of Hibiscus sabdariffa using HPLC with diode array detection coupled to ESI and ion trap MSJOURNAL OF SEPARATION SCIENCE, JSS, Issue 20 2009Inmaculada C. Rodríguez-Medina Abstract The phenolic fraction and other polar compounds of the Hibiscus sabdariffa were separated and identified by HPLC with diode array detection coupled to electrospray TOF and IT tandem MS (DAD-HPLC-ESI-TOF-MS and IT-MS). The H. sabdariffa aqueous extract was filtered and directly injected into the LC system. The analysis of the compounds was carried out by RP HPLC coupled to DAD and TOF-MS in order to obtain molecular formula and exact mass. Posterior analyses with IT-MS were performed and the fragmentation pattern and confirmation of the structures were achieved. The H. sabdariffa samples were successfully analyzed in positive and negative ionization modes with two optimized linear gradients. In positive mode, the two most representative anthocyanins and other compounds were identified whereas the phenolic fraction, hydroxycitric acid and its lactone were identified using the negative ionization mode. [source] Non-disturbing characterization of natural organic matter (NOM) contained in clay rock pore water by mass spectrometry using electrospray and atmospheric pressure chemical ionization modesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 2 2010Sandrine Huclier-Markai We have investigated the composition of the mobile natural organic matter (NOM) present in Callovo-Oxfodian pore water using electrospray ionization mass spectrometry (ESI-MS), atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and emission-excitation matrix (EEM) spectroscopy. The generation of knowledge of the composition, structure and size of mobile NOM is necessary if one wants to understand the interactions of these compounds with heavy metals/radionuclides, in the context of environmental studies, and particularly how the mobility of these trace elements is affected by mobile NOM. The proposed methodology is very sensitive in unambiguously identifying the in situ composition of dissolved NOM in water even at very low NOM concentration, due to innovative non-disturbing water sampling and ionization (ESI/APCI-MS) techniques. It was possible to analyze a quite exhaustive inventory of the small organic compounds of clay pore water without proceeding to any chemical treatment at naturally occurring concentration levels. The structural features observed were mainly acidic compounds and fatty acids as well as aldehydes and amino acids. Copyright © 2009 John Wiley & Sons, Ltd. [source] Comparison of flow injection analysis electrospray mass spectrometry and tandem mass spectrometry and electrospray high-field asymmetric waveform ion mobility mass spectrometry and tandem mass spectrometry for the determination of underivatized amino acidsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2006Margaret McCooeye Twenty proteinogenic amino acids (AAs) were determined without derivatization using flow injection analysis followed by electrospray ionization mass spectrometry and tandem mass spectrometry (ESI-MS and ESI-MS/MS) and electrospray ionization high-field asymmetric waveform ion mobility mass spectrometry and tandem mass spectrometry (ESI-FAIMS-MS and ESI-FAIMS-MS/MS), in positive and negative ionization modes. Three separate sets of ESI-FAIMS conditions were used for the separation and detection of the 20 AAs. Typically ESI-FAIMS-MS showed somewhat improved sensitivity and significantly better signal-to-noise ratios than ESI-MS mainly due to the elimination of background noise. However, the difference between ESI-FAIMS-MS and ESI-MS/MS was significantly less. ESI-FAIMS was able to partially or completely resolve all the isobaric amino acid overlaps such as leucine, isoleucine and hydroxyproline or lysine and glutamine. Detection limits for the amino acids in ESI-FAIMS-MS mode ranged from 2,ng/mL for proline to 200,ng/mL for aspartic acid. Overall, ESI-FAIMS-MS is the preferred method for the quantitative analysis of AAs in a hydrolyzed yeast matrix. Copyright © 2006 Crown in the right of Canada. Published by John Wiley & Sons, Ltd. [source] Determination of organic acids in urine by solid-phase microextraction and gas chromatography,ion trap tandem mass spectrometry previous ,in sample' derivatization with trimethyloxonium tetrafluoroborateBIOMEDICAL CHROMATOGRAPHY, Issue 10 2008Marco Pacenti Abstract A method for the determination of the organic acids directly in the urine employing derivatization with trimethyloxonium tetrafluoroborate as a methylating agent and sequential extraction by head space and direct immersion/solid phase microextraction is reported. Furoic acid, hippuric acid, methylhippuric acid, mandelic acid, phenylglyoxylic acid and trans, trans muconic acid contained in urine and proposed by the American Conference of Governmental Industrial Hygienists as biological exposure indices were determined after a fast and economically convenient preparation step and sensitive gas chromatography,ion trap,mass spectrometry/tandem mass spectrometry analysis. Urine is rather a complex sample and hence the acquisition method required specific GC-MS instrumentation capable of supporting the changeover, fully automated during a single chromatographic separation, from mass to tandem mass spectrometry and both chemical and electron ionization modes. The automation of the analytical method provides a number of advantages, including reduced analysis time for both routine analysis and method development, and greater reproducibility. The equilibrium and kinetics of this substances vs head space/direct immersion-solid phase microextraction were investigated and evaluated theoretically. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||