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At least 181 records · Page 10Linked to original sources
PubMed1983

A retrospective evaluation of mediastinal tomograms, isotope liver scans, and isotope bone scans in the staging and management of patients with lymphoma.

The influence of mediastinal tomograms and isotope scans of liver and bone on the initial staging and management of patients with lymphoma has been studied. There appears to be only a small role for these investigative procedures, and it is suggested that considerable savings in time and money can be made by a more judicious use of these techniques.

Adolescent↗
PubMed2003

Fast high-precision on-line determination of hydrogen isotope ratios of water or ice by continuous-flow isotope ratio mass spectrometry.

A new fast high-precision on-line technique is described for the determination of hydrogen isotope ratios of water by continuous-flow mass spectrometry. For the first time H(2)/H(2)O-equilibration using a platinum catalyst has been used in a fully continuous process. A significant reduction in the H(2)/H(2)O-equilibration time is achieved by a complete vaporization of the water and by increasing the exchange temperature to 100 degrees C. The analysis time is only approximately 5 min/sample which includes equilibration and processing. Measurement precision and accuracy are better than 1 per thousand and sample consumption is only approximately 5 microL. This new technique allows the measurement of a wide range of aqueous samples either in a semi-continuous way (discrete samples are injected one after another) or in a fully continuous way. This allows us, for the first time, to make continuous measurements of ice cores.

Calibration↗
PubMed1992

Simultaneous determination of stable isotopically labelled L-histidine and urocanic acid in human plasma by stable isotope dilution mass spectrometry.

A capillary gas chromatographic-mass spectrometric method for the simultaneous determination of stable isotopically labelled L-histidine (L-[3,3-2H2,1',3'-15N2]histidine, L-His-[M + 4]) and urocanic acid ([3-2H,1',3'-15N2]urocanic acid, UA-[M + 3]) in human plasma was developed using DL-[2,3,3,5'-2H4,2'-13C,1',3'-15N2]histidine (DL-His-[M + 7]) and [2,3,5'-2H3,2'-13C,1',3'-15N2]urocanic acid (UA-[M + 6]) as internal standards. L-Histidine and urocanic acid were derivatized to alpha N-(trifluoroacetyl)-imN-(ethoxycarbonyl)-L-histidine n-butyl ester and imN-(ethoxycarbonyl)urocanic acid n-butyl ester. Quantification was carried out by selected ion monitoring of the molecular ions of the respective derivatives of L-His-[M + 4], DL-His-[M + 7], UA-[M + 3] and UA-[M + 6]. The sensitivity, specificity, precision and accuracy of the method were demonstrated to be satisfactory for measuring plasma concentrations of L-His-[M + 4] and UA-[M + 3] following administration of trace amounts of L-His-[M + 4] to humans.

Gas Chromatography-Mass Spectrometry↗
PubMed2003

Simultaneous determination of endogenous and stable isotope-labelled 6beta-hydroxycortisols in human urine by stable isotope dilution mass spectrometry.

This study describes a capillary GC-MS method for the simultaneous determination of endogenous 6beta-hydroxycortisol (6beta-OHF) and its stable isotope-labelled analogue, 6beta-hydroxy-[1,1,19,19,19-2H(5)]cortisol (6beta-OHF-2H(5)), in human urine. 6beta-Hydroxy-[1,2,4,19-13C(4),1,1,19,19,19-2H(5)]cortisol (cortisol-13C(4),(2)H(5)) was used as an analytical internal standard. The methoxime trimethylsilyl ether (MO-TMS) derivatization was employed for the GC-MS analysis of 6beta-OHF. Quantitation was carried out by selected-ion monitoring (SIM) of the characteristic fragment ion ([M-31](+.)) of the MO-TMS derivative of 6beta-OHF. The sensitivity limit of the present GC-MS-SIM method was found to be 25 pg per injection for 6beta-OHF (S/N ratio=5.6). The within-day reproducibility in the amounts of unlabelled and labelled 6beta-OHFs determined were in good agreement with the actual amounts added, the relative errors being less than 5.30%. The inter-assay RSDs were less than 4.95% for unlabelled and labelled 6beta-OHFs.

Calibration↗
PubMed2001

Sulfur isotope analysis of sulfide and sulfate minerals by continuous flow-isotope ratio mass spectrometry.

A continuous flow method (CF-IRMS) for the rapid determination of the sulfur isotope composition of sulfide and sulfate minerals has significant advantages over the classic extraction method in terms of the reduced sample quantity and a rapid analytical cycle of less than 8 min/ analysis. For optimum performance, the technique is sensitive to a number of operating parameters, including sample weight and the O2 saturation of the Cu-reduction reactor. Raw data are corrected using a calibration based on five international and internal standards ranging from -17.3 to +20.3 per thousand, which requires monitoring in order to correct the effect of changing delta18O of the sample gas on the measured mass 66 values. Measured sulfur contents are within 1-1.5% of expected values and the reproducibility of delta34S values is +/-0.1 per thousand (1sigma). The technique has been used successfully for more than 1000 analyses of geological samples with a wide range of delta34S from -20 to +20 per thousand.

Journal Article↗
PubMed1992

Evaluation of a Salmonella-specific DNA probe by colony hybridization using non-isotopic and isotopic labeling.

A 2.3 kilobase (kb) Salmonella probe, JEO402-1, and two subfragments, F1214 (1.3 kb) and F1217 (0.8 kb), have been evaluated by colony hybridization using pure cultures of Salmonella serovars and non-salmonella bacteria. JEO402-1, and its subfragments, F1214 and F1217, hybridized to all of 156 different Salmonella serovars tested, while there was no reaction to 112 non-salmonella strains belonging to 19 genera and 37 species of Enterobacteriaceae. Together with previously published results, the JEO402-1 probe has now been shown to detect a total of 396 Salmonella strains belonging to 214 serovars of Salmonella subspecies I-VI. A total of 178 non-salmonella strains representing 23 genera and 51 species of Enterobacteriaceae have all tested negative with JEO402-1. The hybridization results obtained using a digoxigenin-labeled probe were similar to those obtained with 35S isotopic labeling when complete colony lysis was ensured.

Bacterial Typing Techniques↗
PubMed1967

Transition-state models and hydrogen-isotope effects. Kinetic isotope effects provide a sensitive test for detailed models of reacting systems.

The transition-state theory of chemical kinetics, coupled with relatively crude methods of constructing potential-energy surfaces for reacting systems, has great utility in the forecasting of kinetic properties. In particular, it permits prediction of the effect of isotopic substitution on rate constants, and comparison of these predictions with experimental data provides a particularly sensitive test for the combination of potential-energy surface and transition-state theory. More rigorous tests of each of these factors depend on future developments in quantum chemistry, in studies of chemical reactions in molecular beams, and in detailed trajectory calculations of scattering processes.

Deuterium↗
PubMed1978

Stable isotope fractionation by Clostridium pasteurianum. 2. Regulation of sulfite reductases by sulfur amino acids and their influence on sulfur isotope fractionation during SO32- and SO42- reduction.

In addition to an assimilatory sulfite reductase, studies of cultures of Clostridium pasteurianum supplemented with methionine, cysteine, and 35SO42- provides evidence for another reductase which is induced by SO32-. This inducible reductase appears to be dissimaltory because of the copious sulfide production arising when the cells are grown on SO32-. Cysteine can repress the assimilatory sulfite reductase but does not affect the inducible reductase. During late logarithmic growth on 1 mM SO42- + 10mM cysteine, depression of the inducible reductase occurred along with increased sulfide production. The presence of 1 mM cysteine and (or) 1 mM cysteine and (or) 1 mM methionine does not affect the inverse sulfur isotope effect for evolved H2S. However, 5 and 10 mM cysteine reduce the maximum delta34S value for released H2S from +40 to 10%. A small conversion of cysteine to H2S by C. pasteurianum occurs, but only in the stationary phase.

Cell-Free System↗
PubMed2006

Isotope-selective excitation of 41Ca isotope in Doppler-free two-photon continuous-wave excitation: a case study.

Seven schemes are studied theoretically for Doppler-free two-photon excitation of rare (41)Ca isotope using single-mode continuous-wave lasers. The ionization efficiencies and optical selectivities for all the schemes are calculated for various powers of the excitation and ionization lasers and for various focusing conditions of the two lasers. To maximize the ionization efficiencies and the optical selectivities, wavelength-dependent Stark compensation is used. Certain laser wavelengths of the ionization step termed as magic wavelengths are identified for compensating the Stark shift induced by the excitation laser. The effects of the Stark-shift-induced asymmetry and its reversal by selecting the appropriate magic wavelength for the ionization step for various excitation and ionization laser intensities are investigated. The ionization efficiency and optical selectivity for the best scheme after Stark compensation are found to be 8.4 x 10(-4) and approximately 9 x 10(3), respectively.

Journal Article↗
PubMed1985

[Exertion isotope tests in coronary insufficiency. Comparison with isotopic ventriculography and myocardial scintigraphy].

Very few studies have been described comparing the value of exercise myocardial scintigraphy and left ventricular angioscintigraphy. The authors designed a study comparing these two investigations with conventional exercise stress testing and coronary angiography. The isotopic investigations were carried out within 48 hours of coronary angiography. A total of 143 patients undergoing coronary angiography (35 normal, 108 coronary patients: 36 single vessel, 36 double vessel and 36 triple vessel disease) were included in this study. The lesions were located of the LAD (77 cases), left circumflex (77 cases) and right coronary arteries (62). The sensitivity and specificity of both radionuclide investigations were evaluated to assess their diagnostic value; the best results were obtained with myocardial scintigraphy (sensitivity 86 p. 100; specificity 100 p. 100); angioscintigraphy had a sensitivity of 71 p. 100 and specificity of 97 p. 100, and conventional exercise stress testing of 42 p. 100 and 70 p. 100 respectively. The sensitivity seemed to increase with the degree of stenosis; although the sensitivity of myocardial scintigraphy increased progressively, that of angioscintigraphy doubled in cases of stenosis 90 p. 100 (stenosis less than 90 p. 100, sensitivity = 37 p. 100; stenosis greater than 90 p. 100, sensitivity = 73 p. 100). The sensitivity of myocardial scintigraphy with respect to the severity of the coronary artery disease was best in cases of right coronary artery stenosis (sensitivity in cases of RCA stenosis = 74 p. 100; sensitivity in LAD stenosis = 58 p. 100; sensitivity in left circumflex stenosis = 43 p. 100). The sensitivity of left ventricular angioscintigraphy was best in LAD stenosis (RCA stenosis = 50 p. 100, LAD stenosis = 64 p. 100, left circumflex stenosis = 36 p. 100). The sensitivity of both investigations was poor in left circumflex artery stenosis even when severely diseased. The sensitivity of both investigations was better in diffuse coronary artery disease: myocardial scintigraphy (single vessel disease: 72 p. 100, double vessel disease: 92 p. 100, triple vessel disease: 94 p. 100), left ventricular angioscintigraphy (61 p. 100, 69 p. 100, and 83 p. 100 respectively). Although the association of these two radioisotopic investigations does not improve diagnostic sensitivity, it does provide more information about the localisation and extension of the coronary artery disease especially in LAD and right coronary artery stenosis. These results suggest that these investigations are complementary in the evaluation of patients with coronary artery disease.(ABSTRACT TRUNCATED AT 400 WORDS)

Coronary Disease↗
PubMed1982

The fate of the hydrogens of phosphoenolpyruvate in the reaction catalyzed by 5-enolpyruvylshikimate-3-phosphate synthase. Isotope effects and isotope exchange.

The condensation reaction of phosphoenolpyruvate and shikimate 3-phosphate catalyzed by 5-enolpyruvylshikimate-3-phosphate synthase is thought to proceed by an addition-elimination mechanism in which C-3 of phosphoenolpyruvate transiently becomes a methyl group in the enzyme-bound intermediate. Results obtained from reactions conducted in H2O, 2H2O, and 3H2O, using unlabeled, [3-2H2]-, or [3-3H,2H]phosphoenolpyruvate, are consistent with the addition-elimination pathway and show that the transient methyl group rotates rapidly. There is substantial discrimination against heavy hydrogen isotopes in both the protonation and deprotonation steps. These results demonstrate the feasibility of determining the stereochemical course of the synthase reaction.

3-Phosphoshikimate 1-Carboxyvinyltransferase↗