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At least 1,765 records · Page 98Linked to original sources
PubMed2006

Determination of azelnidipine in human plasma by liquid chromatography-electrospray ionization-mass spectrometry.

A liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) method for the determination of azelnidipine in human plasma was established. Nicardipine was used as the internal standard (IS). After adjustment to a basic pH with sodium hydroxide solution (0.1 M), plasma samples were extracted with cyclohexane-diethyl ether (1:1, v/v) and separated on a C(18) column with a mobile phase of 20 mM ammonium acetate solution-methanol-formic acid (25:75:0.5, v/v). The electrospray ionization was employed in a single quadrupole mass spectrometer for the determination. The method was linear over the concentration range of 0.05-40 ng/ml. The lower limit of quantification (LLOQ) was 0.05 ng/ml. The intra- and inter-run standard deviations were less than 9.5% and 11.0%, respectively. The method was successfully applied to study the pharmacokinetics of azelnidipine in healthy Chinese volunteers.

Administration, Oral↗
PubMed2006

Determination of palonosetron in human plasma by liquid chromatography-electrospray ionization-mass spectrometry.

A high performance liquid chromatography-electrospray ionization-mass spectrometry (HPLC-ESI-MS) method for the determination of palonosetron (PALO) in human plasma using naloxone as the internal standard (IS) was established. After adjustment to a weakly basic pH with saturated sodium bicarbonate, plasma samples were extracted with ethyl acetate and separated on a Hanbon Lichrospher 5-C18 column with a mobile phase of 40 mM ammonium acetate buffer solution containing 0.04% formic acid-methanol (46:54, v/v). PALO was determined with electrospray ionization-mass spectrometry (ESI-MS). HPLC-ESI-MS was performed in the selected-ion monitoring (SIM) mode using target ions at [M+H]+ m/z 297.2 for PALO and [M+H]+ m/z 328.2 for the IS. Calibration curve was linear over the range of 0.02124-10.62 ng/ml. The lower limit of quantification (LLOQ) was 0.02124 ng/ml. The intra- and inter-run variability values were all less than 10.4%. The method has been successfully applied to determine the plasma concentration of PALO in healthy Chinese volunteers.

Adult↗
PubMed2006

Rotamers of m-cresol cation studied by mass-analyzed threshold ionization spectroscopy.

We have applied two-color resonant two-photon mass-analyzed threshold ionization technique to record the vibrational spectra of the selected rotamers of m-cresol. The adiabatic ionization energies of cis and trans m-cresol are determined to be 66,933+/-5 and 67,084+/-5 cm(-1), respectively. Frequencies of the in-plane ring vibrations 6a, 1, and 9b are measured to be 528, 720, 1167 cm(-1) for the cis and 520, 698, and 1153 cm(-1) for the trans m-cresol cation. This indicates that different orientation of the OH group with respect to the CH(3) group slightly influences these ring vibrations.

Cations↗
PubMed2006

Assessing unregulated ionizing radiation exposures of U.S. populations from conventional industries.

During the latter twentieth century, the public learned to fear perceived threats from emerging technologies. Concern about ionizing radiation became a persistent fear, causing protracted and often pointless debate. The twenty-first century offers new opportunities for this fear to cause public and political upset. Citizens and politicians know little about "normal" radiation exposures caused by conventional industries. This paper summarizes ionizing radiation exposure assessments of several such industries, showing they deliver multiples of background radiation annually to millions of people, with even higher subpopulation doses due to lognormally distributed exposures. Such information may be useful in educating the public and in supporting comparative assessments or other forms of research on potential sources of public radiation exposure in the twenty-first century. By exposing people to information about normal radiation, we may hope to avoid some unfortunate policies and unnecessary regulatory responses, while abating needless public fear during this technologically challenging century.

Humans↗
PubMed2004

Screening of free 17-alkyl-substituted anabolic steroids in human urine by liquid chromatography-electrospray ionization tandem mass spectrometry.

A qualitative liquid chromatography-electrospray ionization tandem mass spectrometry method was developed for screening of the abuse of 4-chlorodehydromethyltestosterone, danazol, fluoxymesterone, formebolone, metandienone, oxandrolone, and stanozolol. The introduced method measures simultaneously nine different 17-alkyl-substituted anabolic androgenic steroids or their unconjugated metabolites in human urine, using methyltestosterone as an internal standard. Sample preparation involved one-step liquid extraction. Liquid chromatographic separation was achieved on a reversed-phase column with methanol-water gradient containing 5 mmol/l ammonium acetate and 0.01% (v/v) acetic acid. Compounds were ionized in the positive mode and detected by multiple reaction monitoring. All steroids within the study could be selectively detected in urine with detection limits of 0.1-2.0 ng/ml. The method showed good linearity up to 250 ng/ml with correlation coefficients higher than 0.9947. With simple and fast sample preparation, low limits of detection, and high selectivity and precision, the developed method provides advantages over the present testing methods and has the potential for routine qualitative screening method of unconjugated 17-alkyl-substituted anabolic steroids in human urine.

Anabolic Agents↗
PubMed2003

A highly efficient and automated method of purifying and desalting PCR products for analysis by electrospray ionization mass spectrometry.

In this work we present a rapid and fully automated method to purify and desalt PCR products prior to analysis by electrospray ionization mass spectrometry. The protocol employs a commercial pipette tip packed with an anion-exchange resin and comprises four primary steps: tip pretreatment, sample loading, rinsing, and sample elution. This tip-based purification/desalting protocol has two distinct advantages over previously published methods. First, the protocol can be performed either manually (1-12 samples at a time), using a standard p10 manual pipette, or in a fully automated microtiter plate format (96 samples at a time) employing standard laboratory robotics. Additionally, the entire protocol from crude PCR product to an "electrosprayable" analyte solution requires only 10 microl of crude product and takes less than 20 min. Using capillary gel electrophoresis, we demonstrate an overall recovery efficiency of approximately 80% and demonstrate the exquisite desalting efficiency with high-performance electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Using an internal mass standard we demonstrate sub-ppm mass measurement error which provides an unambiguous base composition for a 120-mer PCR product.

Bacillus subtilis↗
PubMed2003

Identification and quantification of mutagenic halogenated cytosines by gas chromatography, fast atom bombardment, and electrospray ionization tandem mass spectrometry.

Oxidative modification of nucleic acids has been implicated in carcinogenesis. One potential mechanism involves halogenation by the myeloperoxidase and eosinophil peroxidase systems of phagocytes. In the current studies, three mass spectrometric methods for the in vitro and in vivo analysis of halogenated cytosines and deoxycytidines were compared: gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) with a quadrupole instrument, fast atom bombardment or electrospray ionization (ESI) tandem MS with a four-sector magnetic instrument, and liquid chromatography ESI tandem MS (HPLC-ESI-MS/MS) with an ion-trap instrument. GC-EI-MS with selected ion monitoring of dimethyl-tert-butylsilyl derivatives of nucleobases was the most sensitive method. High-energy collisionally induced dissociation MS/MS analysis with a four-sector magnetic instrument yielded detailed structural information about halogenated nucleoside adducts but required relatively large amounts of material. The most sensitive analysis of intact halogenated deoxycytidine was achieved with extracted ion chromatograms using HPLC-ESI-MS/MS with an ion-trap instrument. Our results indicate that GC-EI-MS is the methodology of choice for ultrasensitive analysis of halogenated cytosines. HPLC-ESI-MS/MS provides greater structural detail for these compounds and may rival GC-EI-MS in sensitivity with more advanced liquid chromatography applications. The mass spectrometric methods we have developed should be useful for evaluating the role of phagocyte-derived oxidants in halogenating nucleobases, nucleosides, and DNA at sites of inflammation.

Bromodeoxycytidine↗
PubMed1990

Effect of ionization on microbial air pollution in the dental clinic.

The use of spray-producing instruments in the dental clinic continuously creates a potentially harmful contamination of the room environment. In the present study a 13.5-kV corona discharge ionizing generator was used in order to investigate the effect of ions on the microbial air pollution of the dental clinic. Samples of microbial air population were collected in 9-cm-diameter plates containing either Bacto-Brain Heart Infusion Agar or Bacto-Mitis Salivarius Agar and exposed to different time periods in various locations of an active dental clinic. Microbial air levels in the dental clinic were significantly reduced with the generator (by 40-50%). The data suggest that the ionizing generator can be used to reduce the microbial air pollution within the dental clinic, thus reducing the environmental hazard of infections to the staff.

Air Ionization↗
PubMed2001

On-line coupling of micro-enzyme reactor with micro-membrane chromatography for protein digestion, peptide separation, and protein identification using electrospray ionization mass spectrometry.

To miniaturize high-performance membrane chromatography, a poly(vinylidene fluoride) membrane medium, employed as the stationary phase, is sandwiched between two poly(dimethylsiloxane) substrates containing the microchannels. The microchannels are fabricated by the capillary molding technique, involving the use of capillaries as the channel template and the fluid inlet/outlet. The micro(micro)-membrane chromatography system is coupled with a micro-enzyme reactor containing immobilized trypsins for performing rapid protein digestion, peptide separation, and protein identification using electrospray ionization mass spectrometry. Separation performance of cytochrome c digest in micro-membrane chromatography is compared with the results obtained from a regular reversed-phase micro-liquid chromatography. The efficacy and the potentials of micro-membrane chromatography in tryptic mapping are reported. On-line integration of the micro-enzyme reactor with micro-chromatographic separation techniques and electrospray ionization mass spectrometry clearly provides a microanalytical platform for automated sample handling, minimized sample loss, and reduced sample consumption. It also provides enhanced detection sensitivity and dynamic range for the analysis of complex protein mixtures such as cell lysates in proteomics research.

Amino Acid Sequence↗
PubMed2001

Ionization of dichlorophenols for their analysis by capillary electrophoresis-mass spectrometry.

In order to develop an advanced analytical method using capillary electrophoresis (CE) for non-volatile environmental pollutants such as endocrine disruptors, combination with mass spectrometry (MS) is necessary for their identification. We chose dichlorophenols (DCPs) as test samples because one of their isomers, 2,4-DCP, is suspected to have endocrine disrupting effects. A preliminary study on their separation by CE-MS was performed using a laboratory-made electrospray ionization (ESI) interface. For the effective ionization of 2,4-DCP at the

Chlorophenols↗
PubMed2001

Determination of haloacetic acids in aqueous environments by solid-phase extraction followed by ion-pair liquid chromatography-electrospray ionization mass spectrometric detection.

Haloacetic acids (HAAs) were determined in different water samples by a new, fast and simple analysis method based on enrichment of 50-ml water samples at pH 1.8 by solid-phase extraction (SPE) followed by liquid chromatography (LC) separation and electrospray ionization mass spectrometric detection in the negative ionization mode. Deprotonated (M-H)-haloacetates and decarboxylated (M-COOH)- ions were detected. Different polymeric SPE sorbents were tested, and LiChrolut EN was found to be the best material for the extraction. Complete LC separation of all compounds could only be achieved by ion-pair chromatography using triethylamine as volatile ion-pairing reagent. The detection limits were in the low microg/l range. High microg/l concentration levels for the chlorinated and brominated haloacetates were found in drinking water from a drinking water treatment plant in Barcelona, and the corresponding tap water. In swimming pool water samples from Catalonia mg/l levels and in surface river water from Portugal microg/l values were detected. These results confirm other recent reports on the ubiquitous occurrence of HAAs in aqueous environments.

Acetates↗
PubMed2002

On-line microdialysis of proteins with high-salt buffers for direct coupling of electrospray ionization mass spectrometry and liquid chromatography.

Mass spectrometry (MS) is one of the most powerful instrumental techniques for protein analysis. The electrospray ionization (ESI) approach is known to be very gentle and at the same time compatible with liquid separation techniques such as HPLC and CE. However, ESI is known to be susceptible to salts and impurities, which often cause a dramatic decrease in sensitivity due to the suppression of the ionization of the product of interest. For this reason, LC-ESI-MS coupling has so far been largely limited to reversed-phase chromatography with its hydro-organic mobile phases. Other chromatographic techniques are typically "linked" to ESI-MS by time consuming, off-line desalting steps. On-line microdialysis has been proposed as a solution to this dilemma. In this paper, we introduce an improved microdialysis system, which enlarges the number of putative applications, thus allowing chromatographic separations of biological compounds to be directly coupled to MS detection with little to no loss in time or chromatographic resolution. Examples include separations by affinity, ion-exchange and size-exclusion chromatography, all of which were connected successfully to the ESI-MS detector via the on-line microdialyzer. We propose that, using this system, any kind of chromatography technique can be coupled to ESI-MS, thus enabling for example application in quality control or process monitoring of many bioproduction and downstream processes.

Animals↗
PubMed2002

Analysis of ergosteroids. VIII: Enhancement of signal response of neutral steroidal compounds in liquid chromatographic-electrospray ionization mass spectrometric analysis by mobile phase additives.

The signal response of moderately polar to nonpolar neutral steroidal compounds in positive ion mode was significantly improved in electrospray ionization mode by addition of volatile organic acids (trifluoroacetic acid, acetic and formic) at concentrations much lower than those normally employed for high-performance liquid chromatographic separations of ionic compounds. Each of the three acids enhanced the sensitivity, the order being: formic acid (approximately 50-200 ppm, v/v) > acetic acid (100-500 ppm) > trifluoroacetic acid (5-20 ppm). Higher concentrations caused decrease in the sensitivity. The extent of increase in the sensitivity was compound specific and also depended on the nature of organic modifier present in the mobile phase. Acetic acid was the acid of choice for the 'wrong-way-round' ionization of sulfate conjugates. The postcolumn addition of silver nitrate produced highly stable (M + Ag)+ adducts with concomitant increase in signal response and reduction in baseline noise.

Acetic Acid↗
PubMed2002

Application of liquid chromatography-electrospray ionization tandem mass spectrometry to the detection of 10 sulfonamides in honey.

Liquid chromatography (LC) in combination with tandem mass spectrometry (MS-MS) has been applied to the separation and detection of 10 different sulfonamides in honey. The methodology encompasses a simple hydrolysis of the honey sample to liberate sugar-bound sulfonamides followed by liquid-liquid extraction of the 10 analytes, filtration, and analysis by LC-MS-MS. Conditions for reversed-phase LC and electrospray ionization (ESI) MS-MS in the positive ion mode were optimized for the 10 compounds under study, monitoring two characteristic mass transitions simultaneously for each analyte. The procedure is a qualitative confirmatory method for 10 sulfonamides at the low microg/kg level in honey. Typical recoveries of the analytes in honey ranged from 44 to 73% at a fortification level of 50 microg/kg. This study also addresses the issue of matrix-induced suppression of ionization, an effect often encountered in trace residue analysis of food matrices using LC-ESI-MS-MS based methods.

Calibration↗
PubMed2003

Comparison of separation conditions and ionization methods for the liquid chromatography-mass spectrometric determination of sulfonamides.

The effects of the type and concentration of buffer, composition of the mobile phase and the ionization mode, used for the separation and detection of sulfonamides with LC-MS, were studied. Five typical sulfonamides were selected as target compounds and beef meat was selected as a matrix sample. For the separation of sulfonamides, 0.05 M NH4Ac in 13-15% aqueous acetonitrile, APCl ionization was more effective than ESI with regard to separation efficiency and the detection sensitivity.

Chromatography, Liquid↗
PubMed1990

Health effects of ionizing radiation.

Although humans have evolved in an environment of ionizing radiation, it was not until man-made sources were developed that the effects of ionizing radiation started to become known. Detection and measurement of radiation is not only sophisticated but widely applied. This article deals with exposure to this kind of radiation and the risk it may cause.

Accidents↗
PubMed2006

Hydrogen-deuterium exchange analyzed by matrix-assisted laser desorption-ionization mass spectrometry and the HET-s prion model.

Hydrogen/deuterium (H/D) exchange analyzed by mass spectrometry (HXMS) is a valuable tool for the investigation of protein conformation and dynamics. After exchange, the sample is generally submitted to electrospray ionization for mass analysis. Matrix-assisted laser desorption ionization (MALDI) has been used in a limited number of studies but has several significant advantages that include simplification of the spectra attributable to a predominance of singly charged ions, speed of analysis, sensitivity, and low H/D back-exchange level. MALDI-HXMS has been used to study amyloid aggregates from the HET-s prion protein. Our results underline the ability of this method to determine solvent accessibility within the amyloid aggregates, reaching a resolution of one to four amino acids. To achieve a complete peptide mass fingerprint of the protein, we have taken benefits of an ion trap operating in liquid chromatography-MS/MS mode. MALDI time-of-flight-MS was then used to determine deuterium incorporation within each peptide along the sequence of HET-s. The combined advantages of these two instruments yield a suitable solution for HXMS experiments that require highly resolved peptide mass fingerprints, high sensitivity, and speed of analysis for deuterium incorporation measurements.

Deuterium Exchange Measurement↗
PubMed1997

Hippocampal lesions induced by ionizing radiation: a parametric study.

The selective lesion of granule cell populations in the dentate gyrus induced by ionizing radiation has been proposed as a useful method for evaluating the effects of hippocampal lesions on behavioral tasks. In the first part of the present study we confirmed the induction of the selective lesion of hippocampal dentate gyrus by ionizing radiation in infant Wistar rats, reported previously, but to a smaller extent with less cell loss. A parametric study was thus performed to assess the effect of modification of the parameters previously tested, comprising three further steps: an increase in the total dose of X-rays and modification of the fractionating schedule; use of three radiation types, X-ray, gamma-ray, and electrons (at two energy levels, 3 and 7 mev); use of three X-ray energy levels, 180, 200 and 250 kVp; and assessment of the effect of five total X-ray doses, at 200 kVp, 10, 14, 16, 18 and 20 gy (grays). The data suggests that X-ray radiation, in a total dose of 14 gy, at the 200 kVp energy level, fractionated into seven consecutive exposures of 2 gy each and produces a lesion of about 85% of the dentate gyrus granule cells.

Animals↗