Trace analysis of the oxazaphosphorines cyclophosphamide and ifosfamide in body fluids

no abstrac

Ionization mechanisms in capillary supercritical fluid chromatography-chemical ionization mass spectrometry

Ionization mechanisms have been studied for supercritical fluid chromatography (SFC) with mass spectrometric (MS) detection. One of the problems associated with SFC-MS is the interference of mobile phase constituents in the ionization process, which complicates the interpretation of the resulting mass spectra. This interference can be reduced by adding a reagent gas to the ion source. It was found that the properties and the pressure of this reagent gas control the ionization process. In this study ammonia was used as a chemical ionization (CI) reagent gas. An increase in the reagent gas pressure generally resulted in higher abundances of the protonated molecular ion. The presence of an excess of reagent gas suppresses charge exchange processes between the mobile phase constituents and the solutes. Charge exchange causes a more pronounced fragmentation than proton transfer in CI processes. The spectra obtained by charge exchange ionization, with helium as the reagent gas at moderately high pressures, are comparable to electron ionization spectra from standard MS libraries

Capillary chromatography in cancer research

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Optimization of temperature programming in gas chromatography with respect to separation time. I. Temperature programme optimization fundamentals

The ranges of separbility of neighbouring component pairs in a given mixture, separated isothermally on a given chromatographic column, are defined. These ranges are calculated by approximation functions fitted to the measured values of the retention times and peak widths during isothermal analyses. The sequence of the most difficult to separate component pairs is determined within the temperature separability ranges of the component pairs of the mixture. This sequence determines the strategy for calculation of the optimum temperature programme, and every step of this sequence determines the substrategy. The purpose of the strategy is to find the optimum temeprature trajectory (programme) and the purpose of the substrategy is to find the optimum subtrajectory, i.e., a part of the optimum trajectory. The determination of the strategy and the corresponding substrategies is presented for mixtures of components that do not change their mutual position during isothermal separations within the whole temperature rang

Retention behavior of conjugated and isolated n-alkadienes. Identification of n-nona- and n-decadienes by capillary gas chromatography using structure-retention correlations and mass spectrometry

The isomerization products of n-C8---C10 a,¿-alkadienes were separated on a high-efficiency squalane column (195 m × 0.25 mm I.D.) with 500,000 effective plates. Of the 102 possible n-C8---C10 dienes with isolated and conjugated double bonds, only nine groups of isomers were not separated. All isomers, except those with cumulated double bonds, were identified (23 octadienes, 33 nonadienes and 46 decadienes). The n-octadienes were identified by matching measured and published retention data. Because of the lack of standards, retention data and mass spectra of n-nona- and decadienes, and because the previously reported identification method for n-dienes up to C8 was succesful, the problem of the identification of C9---C10 n-alkadienes was solved similarly by using structure-retention correlations and combined capillary gas chromatography-mass spectrometry. Based on these results, the retention behaviour of the conjugated and isolated n-alkadienes, on squalane stationary phase, is generalized