Evaluation of time-of-flight mass spectrometric detection for fast gas chromatography.

Separations below 1 s of a mixture of organic compounds ranging from C5 to C8 have been performed to investigate the performance of a time-of-flight mass spectrometer in fast gas chromatography. The gaseous samples were focussed on a cold trap, and then injected after thermal desorption to obtain the required narrow input band-widths. Also, to obtain a very fast separation, a short narrow bore column was used, operated at above-optimum inlet pressures. With this system, it was possible to identify ten compounds within 500 ms, showing peak-widths (2.354sigma) as narrow as 12 ms. The spectral acquisition rate used for these analyses was 500 Hz. The quality of the recorded spectra and the comparison with library spectra was very high. Deconvolution algorithms offer the possibility of identifying overlapping peaks. It is shown that the spectral scan speed of the time-of-flight mass spectrometer is high enough for very fast separations.

High-speed gas chromatography: an overview of various concepts.

An overview is given of existing methods to minimise the analysis time in gas chromatography (GC) being the subject of many publications in the scientific literature. Packed and (multi-) capillary columns are compared with respect to their deployment in fast GC. It is assumed that the contribution of the stationary phase to peak broadening can be neglected (low liquid phase loading and thin film columns, respectively). The treatment is based on the minimisation of the analysis time required on both column types for the resolution of a critical pair of solutes (resolution normalised conditions). Theoretical relationships are given, describing analysis time and the related pressure drop. The equations are expressed in reduced parameters, making a comparison of column types considerably simpler than with the conventional equations. Reduction of the characteristic diameter, being the inside column diameter for open tubular columns and the particle size for packed columns, is the best approach to increase the separation speed in gas chromatography. Extremely fast analysis is only possible when the required number of plates to separate a critical pair of solutes is relatively low. Reducing the analysis time by reduction of the characteristic diameter is accompanied by a proportionally higher required inlet pressure. Due to the high resistance of flow of packed columns this seriously limits the use of packed columns for fast GC. For fast GC hydrogen has to be used as carrier gas and in some situations vacuum-outlet operation of capillary columns allows a further minimisation of the analysis time. For fast GC the columns should be operated near the conditions for minimum plate height. Linear temperature programmed fast GC requires high column temperature programming rates. Reduction of the characteristic diameter affects the sample capacity of the "fast columns". This effect is very pronounced for narrow-bore columns and in principle non-existing in packed columns. Multi-capillary columns (a parallel configuration of some 900 narrow-bore capillaries) take an intermediate position.

Gas chromatography-mass spectrometry and high-performance liquid chromatographic analyses of thermal degradation products of common plastics.

The thermo-oxidation of five commonly used materials, namely low-density polyethylene, retarded polyethylene, paper with a polyethylene foil, a milk package and filled polypropylene, was studied. Capillary gas chromatography and gas chromatography-mass spectrometry were used to analyze the volatile degradation products, while high-performance liquid chromatography was employed to measure polycyclic aromatic hydrocarbons. The results are discussed from the point of view of toxicity of the products.

Monitoring the behaviour of 4-ketocyclophosphamide versus cyclophosphamide during capillary gas chromatography by mass spectrometry.

Capillary Gas Chromatography (CGC) is capable of determining underivatized cyclophosphamide (CPA) using SCOT OV 275 columns. Then CPA is subjected to in situ degradation resulting in formation of a cyclization product which can be determined selectively in biological fluids. In routine bioanalysis however cyclization products of CPA metabolites might interfere, e.g. 4-keto CPA. In the present study possible formation of cyclization products of 4-keto CPA similar to CPA was monitored by Mass Spectrometry. Cyclization of 4-keto CPA in situ was demonstrated to occur, resulting in a product similar to that of CPA. Both cyclization products could be determined selectively and it appeared that in situ cyclization of 4-keto CPA was negligible (less than 5%), probably owing to extra stabilization of the CPA metabolite by keto-enol tautomerism as has been demonstrated by NMR.

Determination of the underivatized antineoplastic drugs cyclophosphamide and 5-fluorouracil and some of their metabolites by capillary gas chromatography combined with electron-capture and nitrogen-phosphorus selective detection.

A rapid and sensitive method for the determination of cyclophosphamide (CP) and 5-fluorouracil (5-FU) and some of their metabolites in one analysis has been developed. Surface-coated open-tubular OV-275 columns were combined with electron-capture detection and nitrogen-phosphorus selective detection. The influence of the column diameter on the separation is shown. Extraction with 2-propanol-diethyl ether (22:77) allows the isolation of CP, 5-FU and their analogues in one extraction step. The assay was applied to some pharmacokinetic experiments with chemotherapeutically treated patients and with a WAG/Rij rat.

Chemical ionization mass spectrometry of trimethylsilylated carbohydrates and organic acids retained in uremic serum.

After appropriate sample pretreatment and derivatization, uremic serum was investigated by combined high resolution gas chromatography and mass spectrometry, using both electron impact and chemical ionization methods. Electron impact and chemical ionization spectra of a number of identified (trimethylsilylated) carbohydrates and organic acids are compared. The utilization of chemical ionization mass spectrometry, with isobutane as the reagent gas, is discussed in detail. The influence of the reagent gas pressure on the total ion current and on the spectral appearance was studied. The identification of compounds, based on electron impact mass spectral data, was confirmed and often aided appreciably by using this technique. The chemical ionization spectra of trimethylsilyated alditols and aldonic acids, as well as of other organic acids showed protonated molecular ions, whereas aldoses did not. Differences with electron impact spectra are found mainly in the high mass region. The loss of one or more trimethylsilanol groups becomes the predominating fragmentation route at higher reagent gas pressures.

Possibilities and limitations of capillary gas chromatography and mass spectrometry in the analysis of polychlorinated biphenyls.

The possibilities and limitations of analyses of polychlorinated biphenyls (PCBPs) by capillary gas chromatography and capillary gas chromatography-mass spectrometry have been investigated. Metal capillary columns (WCOT) coated with Apiezon L and OV-101 were not suitable for PCB analyses. Good results were obtained in the separation of model mixtures of PCBs and of Aroclor 1242 on a glass capillary column coated with OV-101. Sources of error are indicated that may be encountered in the characterization of PCB components in Aroclor 1242 by standard additions, Kováts' retention indices and mass spectrometry. The direct coupling of a capillary column (WCOT) to a mass spectrometer produced spectra of the main PCB components, many of which could be used in the identification of isomeric PCBs.