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PubMed2001

Evaluation of AVL988/4 analyzer for measurement of ionized magnesium and ionized calcium.

Ionized magnesium (Mg++) and ionized calcium (Ca++) are the physiologically active forms of these elements in the body and their concentrations have clinical value. Though the AVL988/4 instrument that measures concentrations of Mg++ and Ca++ has been evaluated, some clinically important parameters were unknown. In this study, we evaluated AVL988/4 analyzer for measuring Mg++ and Ca++ concentrations and provided the following information: (1) The newly formulated Becton Dickinson (BD) Vacutainer plastic tubes with clot activator and silicone as the stopper lubricant (serial no. 367820) caused a significant high bias for the Mg++ measurement but had no effect on the Ca++ measurement; (2) the optimal conditions for specimen storage were no exposure to air at 4 degrees C for up to 24 h; (3) no significant difference in the results of the Ca++ concentration determined using AVL988/4 or i-STAT; (4) no carryover between samples was found.

Autoanalysis↗

PubMed2000

Ionization processes and charge-state distribution in a highly ionized high- Z laser-produced plasma

The charge-state distribution in a well-characterized highly ionized Au plasma was accurately determined using time-resolved x-ray spectroscopy. Simultaneous measurements of the electron temperature and density allow the first direct comparisons with nonlocal thermodynamic equilibrium model predictions for the charge-state distribution of a highly ionized high- Z plasma in a nonradiative environment. The importance of two-electron atomic processes is clearly demonstrated.

Journal Article↗

PubMed2006

Interference oscillations in the angular distribution of laser-ionized electrons near ionization threshold.

We analyze the two-dimensional momentum distribution of electrons ionized by few-cycle laser pulses in the transition regime from multiphoton absorption to tunneling by solving the time-dependent Schrödinger equation and by a classical-trajectory Monte-Carlo simulation with tunneling (CTMC-T). We find a complex two-dimensional interference pattern that resembles above threshold ionization (ATI) rings at higher energies and displays Ramsauer-Townsend-type diffraction oscillations in the angular distribution near threshold. CTMC-T calculations provide a semiclassical explanation for the dominance of selected partial waves. While the present calculation pertains to hydrogen, we find surprising qualitative agreement with recent experimental data for rare gases [A. Rudenko, J. Phys. B 37, L407 (2004)].

Journal Article↗

PubMed1984

The ionization of beta-adrenoceptor agonists: a method for unravelling ionization schemes.

To investigate the ionization schemes of beta-adrenoceptor agonists, a combined electrochemical/uv-spectrophotometric method with computer-assisted data-analysis was developed, yielding the macroscopic and microscopic ionization constants. From the four species possible, cations and zwitterions were found the main species present at physiological pH, the formation of uncharged molecules and anions being less favourable or apparently negligible.

Adrenergic beta-Agonists↗

PubMedDate not supplied

Fraction of ionization from electrons arising in the wall of an ionization chamber.

The accuracy of high-energy x-ray dosimetry can be improved by taking account of differences between the compositions of the chamber wall and the buildup cap or dosimetry phantom. The fraction of the ionization due to secondary electrons arising in the chamber wall has been determined as a function of wall thickness for 60Co gamma rays and x rays in the range of 2-25 MV for Farmer-type chambers. Secondary electrons arising in the accelerator head were removed from the x-ray beams by a magnetic field placed just in front of the ionization chamber. For 60Co gamma rays, the fraction increases from 40% to 100% as the wall thickness increases from 0.05 to 0.55 g cm-2. For a 0.05 g cm-2 wall, fraction decreases from 60% to 10% as the x-ray energy is increased from 2 to 25 MV. Limited data obtained with different chambers suggest that the fraction is independent of chamber wall composition when the thickness is expressed in g cm-2.

Cobalt Radioisotopes↗

PubMed2003

Analyses of anandamide and endocannabinoid-like compounds using collision-induced dissociation in fast atom bombardment ionization-mass spectrometry and gas chromatography/chemical ionization-mass spectrometry.

The utility of the collision-induced dissociation (CID) of two different forms of precursor cations generated by the fast atom bombardment (FAB) ionization of N-arachidonylethanolamine (anandamide) and a series of endocannabinoid-like compounds, such as N-oleoylethanolamine, N-palmitoylethanolamine, N-stearoylethanolamine, N-linoleoylethanolamine, N-oleoylpropanolamine, and N-palmitoylpropanolamine, as a method of providing general information on their characterizations was examined. The CID spectra of lithium-adduct [M+Li]+ ions of the amines with unsaturated hydrocarbon chains were rich in structurally informative charge-site-remote (CSR) fragmentation patterns that provide information on the locations of double bonds in hydrocarbon chains. On the other hand, the CID reactions of [M+H]+ ions produced acylium ions that are derived from the cleavage of amide bonds, thus providing information on the size of the hydrocarbon chains, although CSR fragmentations were not observed. These compounds without derivatization were analyzed using gas chromatography/chemical ionization-mass spectrometry (GC/CI-MS) with a polyethylene glycol phased column with fused silica capillary pre-tubing. Identifiable molecular-related [M+H]+ ions were observed.

Arachidonic Acids↗

PubMed2002

Enhancement of ionization efficiency by electrochemical reaction products in on-line electrochemistry/electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.

A miniaturized two-electrode electrochemical (EC) cell was developed and was coupled on-line with an electrospray ionization Fourier transform ion cyclotron resonance mass spectrometer (ESI-FTICR MS). Electrochemistry on-line with mass spectrometry, EC/ESI-FTICR MS, of triphenylamine (TPA), which undergoes one-electron oxidation to form a radical cation (TPA*+), demonstrates a significant sensitivity enhancement compared to ESI-FTICR MS. The on-line EC cell configuration with a stainless steel ES needle as the working electrode produces the highest sensitivity in EC/ESI-MS. The results provide evidence that, during the ES ionization, electrolytic reactions occur mainly in the ES tip region, as previously predicted. The results demonstrate that ESI-MS signal suppression by tetrabutylammonium perchlorate electrolyte, which can be a problem, is minimized in EC/ESI-MS. TPA*+ dimer tetraphenylbenzidine (TPB) can be detected by EC/ESI-MS, together with TPA*+, as TPB*+ and TPB2+. The high mass resolving power of FTICR MS was exploited to identify TPB2+ dication in the presence of [TPA*+ - H*]+ ions of the same m/z, from their respective isotopic distributions. The dimer dication TPB2+ can be detected only in EC/ESI-MS.

Journal Article↗

PubMed1992

Interaction of photodynamic treatment and either hyperthermia or ionizing radiation and of ionizing radiation and hyperthermia with respect to cell killing of L929 fibroblasts, Chinese hamster ovary cells, and T24 human bladder carcinoma cells.

Both hyperthermia and photodynamic therapy of cancer are frequently used in combination with other treatment modalities in order to improve tumor control with minimal damage to normal tissues. The present results indicate that the most effective combination of treatment modalities is different in different cell types. For instance, ionizing irradiation and hyperthermia exhibited additivity when applied to L929 fibroblasts, in contrast to the synergistic interaction described before in many other cell lines. This aberrant behavior of L929 cells could be explained by the relative insensitivity of DNA repair in these cells to hyperthermia. Conversely, a synergistic interaction between photodynamic treatment and ionizing irradiation was observed with L929 fibroblasts, whereas these treatments were additive with Chinese hamster ovary and T24 cells. The synergistic interaction with L929 cells could be explained by the high sensitivity of DNA repair in these cells to photodynamic treatment. Photodynamic treatment and hyperthermia exhibited a synergistic interaction in L929, Chinese hamster ovary, and T24 cells. The critical target for cell killing by the combined treatment protocol in these cell lines has not yet been elucidated. In all three cell lines, however, analysis of the results according to the Arrhenius equation revealed a photodynamically induced change of both the frequency factor and the activation energy of subsequent thermal cell killing. It is considered that this may indicate a basic mechanism, in which a particular protein is a common, critical target of the two modalities of treatment.

Animals↗

PubMed1995

Analyzer-dependent differences in results for ionized calcium, ionized magnesium, sodium, and pH.

We compared two ion-selective analyzers (AVL 988-4 and NOVA CRT) for determining ionized calcium (iCa2+), ionized magnesium (iMg2+), sodium (Na+), and pH in serum specimens from healthy and diseased individuals. For assays of three levels of protein-based control materials, total imprecision (CV) was < 3% for all analytes except iMg2+ (< or = 6.5% on NOVA, and < or = 4.9% on AVL). We found a significant difference between the analyzers (P < 0.001) for the mean iMg2+ concentration in patients but no significant correlation (r = 0.253) between the analyzers for iMg2+ in specimens from healthy volunteers, even though the mean iMg2+ concentration did not differ significantly between these groups. The reference interval (central 95 percentiles) for iMg2+ with AVL (0.44-0.60 mmol/L) was contained within that of NOVA (0.39-0.64 mmol/L). The AVL gave higher values for iCa2+ (P < 0.001) and lower values for pH (P < 0.001) in specimens from normal volunteers and patients. The mean value for Na+ in patients' samples was significantly higher by the NOVA (P < 0.01) than by the AVL analyzer. Thus, we found significant differences between these two analyzers for all four analytes.

Calcium↗

PubMed1998

Dynamics of ionized magnesium and ionized calcium during recovery from diabetic ketoacidosis managed with conventional treatment.

Serial measurements of ionized magnesium (iMg), ionized calcium (iCa) and pH performed during the management of diabetic ketoacidosis (DKA) in a 10 9/12-year-old female showed a progressive decrease in iMg and iCa to subnormal values which inversely correlated with the increase of pH, suggesting a state of depletion of these cations during conventional DKA management.

Calcium↗

PubMed2001

Analysis of regulatory phosphorylation sites in ZAP-70 by capillary high-performance liquid chromatography coupled to electrospray ionization or matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

A methodology for the rapid and quantitative analysis of phosphorylation sites in proteins is presented. The coupling of capillary high-performance liquid chromatography (HPLC) to electrospray ionization mass spectrometry (ESI-MS) allowed one to distinguish phosphorylation sites based on retention time and mass difference from complex peptide mixtures. The methodology was first evaluated and validated for a mixture of non-, mono-, and dityrosine-phosphorylated synthetic peptides, corresponding to the tryptic fragment 485-496 (ALGADDSYYTAR) of the human protein tyrosine kinase ZAP-70. The limits of detection for the non-, mono- and diphosphorylated peptides were about 15, 40 and 100 fmol, respectively, when using a 300 microm I.D. column. Application of the method was extended to identify phosphopeptides generated from a trypsin digest of recombinant autophosphorylated ZAP-70, in particular with respect to quantifying the status at the regulatory phosphorylation sites Tyr-492 and Tyr-493. Combination of chromatographic and on-line tandem mass spectrometry data allowed one to ascertain the identity of the detected peptides, a prerequisite to analyses in more complex biological samples. As an extension to the methodology described above, we evaluated the feasibility of interfacing capillary HPLC to matrix assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS), using a micromachined piezoelectric flow-through dispenser as the interface. This enabled direct arraying of chromatographically separated components onto a target plate that was precoated with matrix for subsequent analysis by MALDI-TOF-MS without further sample handling.

Amino Acid Sequence↗

PubMed1998

Identification of phosphorylated proteins from thrombin-activated human platelets isolated by two-dimensional gel electrophoresis by electrospray ionization-tandem mass spectrometry (ESI-MS/MS) and liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS).

Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) is a powerful tool to separate complex protein mixtures including whole cell lysates. In combination with immunoblotting techniques or radioactive labeling techniques it is a fast and convenient way to demonstrate the presence of certain proteins or protein modifications. With the development of extremely sensitive analytical techniques such as matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) or electrospray ionization (ESI)-MS, it has become possible to use 2-D gels not only as an analytical but also as a preparative tool. Starting with a number of spots excised from 2-D gels, a protein can be identified using different strategies involving enzymatic cleavage of the protein in the gel matrix, elution of the resulting peptides and analysis of these peptides by mass spectrometry. The obtained peptide mass fingerprint or fragment ion spectra from peptides can be used to screen protein or nucleic acid databases in order to identify the protein. We have used the techniques described above to identify proteins from human platelets which change their phosphorylation state following activation of platelets by thrombin. Platelets were radioactively labeled with [32P]orthophosphate and stimulated. Several protein spots in the observed range of 10-80 kDa and an isoelectric point of 3-10 showed a significant increase or decrease in phosphorylation. We present the results from the investigation of a spot group representing different isoforms and phosphorylation states of myosin light chain.

Amino Acid Sequence↗

PubMed2004

Analysis of 21-deoxycortisol, a marker of congenital adrenal hyperplasia, in blood by atmospheric pressure chemical ionization and electrospray ionization using multiple reaction monitoring.

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder mainly caused by 21-hydroxylase deficit (21-OHD). Deletions or mutations of the CYP21 gene induce the impairment of glucocorticoid and mineralcorticoid synthesis. 17-Hydroxyprogesterone (17-OHP) is the hormonal marker in patients, but not in the heterozygous subjects. Excess 17-OHP is hydroxylated into 21-deoxycortisol (21-DF), and therefore 21-DF can be used as a specific marker for diagnosis of heterozygous individuals. We report an analytical method for analysis of 21-DF in blood samples using electrospray (ESI) and atmospheric pressure chemical ionization (APCI), showing that ESI is very sensitive for the analysis of this marker molecule. The multiple reaction monitoring (MRM) approach was used to increase the specificity and the sensitivity of the method.

Adrenal Hyperplasia, Congenital↗

PubMed2004

Capillary high-performance liquid chromatography-electrospray ionization mass spectrometry using monolithic columns and carbon fiber electrospray ionization emitters.

Monolithic columns having long hydrocarbon chains were prepared by in-situ polymerization in capillary fused silica tubing. The capillary columns were coupled with a newly developed carbon fiber electrospray ionization (ESI) emitter for proteomic analysis using sheathless capillary HPLC-ESI mass spectrometry (MS). The sample loading capacity and chromatographic performance of the styrene-based monolithic column, which was prepared by photo-polymerization of octylstyrene (OS) and divinylbenzene (DVB) were compared with that of the methacrylate-based monolithic column composed of lauryl methacrylate (LMA) and ethylene dimethacrylate (EDMA). The sample loading ability of tryptic digested protein in poly-OS (POS)-DVB column was higher than that of poly-LMA (PLMA)-EDMA column, possibly due to the irregular and rugluous surface offering a greater surface area of POS-DVB stationary phase. The POS-DVB column also provided better separation efficiency in the separation of high concentration (10 microg) of tryptic digested albumin bovine serum (BSA). Due to the successful interface of a highly efficient monolithic column and a stable, durable carbon fiber emitter, low femtomole levels of peptides were successfully separated and identified in the presence of large amounts of tryptic digested protein.

Amino Acid Sequence↗

PubMed2001

Characterization of ageing products of ester-based synthetic lubricants by liquid chromatography with electrospray ionization mass spectrometry and by electrospray ionization (tandem) mass spectrometry.

Ageing products of a commercial jet engine oil based on pentaerythritol tetraesters which were formed upon operation in an aviation turbine were detected by electrospray ionization mass spectrometry (ESI-MS) and characterized by LC-ESI-MS. The fatty acid composition of these ageing products was investigated by ESI-MS-MS analysis. The ammonium adducts of the newly formed pentaerythritol tetraester degradation products were found to be suitable parent ions for further structure elucidation work. ESI-MS, LC-ESI-MS and ESI-MS-MS proved to be versatile tools to study the chemical composition (distribution of homologues) as well as the mechanism of ageing of ester based lubricants on a molecular level. Due to its high sensitivity, ESI-MS can also be used to characterize and identify trace levels of ester-based lubricants.

Chromatography, Liquid↗

PubMed2000

Determination of ionization efficiency of glycated and non-glycated peptides from the N-terminal of hemoglobin beta-chain by electrospray ionization mass spectrometry.

We compared the ionization efficiency of glycated and non-glycated peptides for the HbA1c measurement method developed by Kobold et al. [Clin. Chem., 43 (1997) 1944] based on LC-ESI-MS analysis of the N-terminal peptides of the beta-chains released by cleavage of the hemoglobin with endoproteinase Glu-C. Taking half the peak area of the doubly charged ion and adding it to the area of the singly charged ion, we determined that the slope of the resulting calibration curve was nearly equal to 1, and the reproducibility of the added values was better than the values calculated by the doubly or the singly charged ion alone.

Calibration↗

PubMed1999

Do charge-remote fragmentations occur under matrix-assisted laser desorption ionization post-source decompositions and matrix-assisted laser desorption ionization collisionally activated decompositions?

The precursor ions of tetraphenylporphyrins that are substituted with fatty acids can be introduced into the gas phase by matrix-assisted laser desorption ionization (MALDI) and undergo post-source and collisionally activated decompositions (CAD) in a time-of-flight mass spectrometer. The goal of the research is to obtain a better understanding of post-source decompositions (PSD); specifically, we asked the question of whether ions undergoing PSD have sufficient energy to give charge-remote fragmentations along an alkyl chain. We chose the porphyrin macrocycle because we expected it to act as an inert "support," allowing the molecule to be desorbed by MALDI and to be amenable to charge-remote fragmentation. MALDI-PSD and MALDI-CAD spectra are similar to high-energy CAD spectra and considerably more informative than low-energy CAD spectra, showing that charge-remote fragmentations of the fatty acid moieties do occur upon MALDI-PSD and MALDI-CAD.

Fatty Acids↗

PubMed1999

Differentiation of isomeric photomodified oligodeoxynucleotides by fragmentation of ions produced by matrix-assisted laser desorption ionization and electrospray ionization.

UV irradiation of oligodeoxynucleotides at 254 nm generates several different types of DNA photoproducts, including cis-syn cyclobutane pyrimidine dimers, pyrimidine[6-4] pyrimidone photoproducts and their Dewar valence isomers, and thymine-adenine photoproducts (TA*). Studies of photoproducts in oligodeoxynucleotides require the development of suitable structure determination methods such as mass spectrometry. In an earlier study (Vollmer et al. Int. J. Mass Spectrom. Ion Processes 1997, 165/166, 487-496), we showed that fast atom bombardment and tandem sector mass spectrometry can be used to locate the site of photomodification and identify most of the photoproducts of d(TATTAT). One goal of the present research was to expand the method to the more sensitive electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) methods. A second goal was to test the generality of the methods by investigating not only the photoproducts of d(TATTAT) but also those of three other oligodeoxynucleotides, d(GTATTAT), d(GGCTATAA), and d(AATTAA). The photoproducts of these sequences were separated by HPLC and gave characteristic fragment ions in postsource decompositions of MALDI-produced ions and collisionally activated decompositions of ESI-produced ions.

Algorithms↗