József Balla

Response of flame ionization detectors to different homologous series

SummaryHydrogen flame-ionization detectors (FIDs) are the most widely used type of detector in gas chromatography. The FID signals is proportional to the number of carbon atoms in a hydrocarbon molecule; the presence of heteroatoms usually reduces the signal. If the extent of the signal-reducing effect of heteroatoms were known, it would be possible to measure compounds which are not available as pure standards, or cannot be prepared, or their preparation is very expensive. The sensitivity of a detector to an organic molecule containing heteroatoms is referred to normal hydrocarbons by means of the effective carbon-atom number (ECN) value. By use of the values of increments inECN for heteroatoms and functional groups, theECN can be calculated for any organic molecule. For this, exact values of theECN increments are needed, and the effects of different factors on the increments must be known. In this study a wide range of homologues of normal paraffins, alcohols, amines, and esters was investigated, with emphasis on differences between the behaviour of lower and higher homologues. Studies were extended to theECN values of ketones, and aromatic and halogenated compounds. For all types of compound investigated the difference between the actual carbon number and the calculated effective carbon number (dECN) was compared with literature data, and an attempt was made to interpret the differences.

Gas-liquid chromatographic analysis of dimedone derivatives of formaldehyde and other aliphatic aldehydes on capillary columns

Abstract The quantitative determination of small amounts of aliphatic aldehydes (formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde) in biological samples is difficult by the classical methods. The dimedone derivatives of these aldehydes were prepared and proved to be stable under the conditions of gas chromatography. The thermal properties of these derivatives were studied by thermal gravimetry, differential scanning calorimetry and thermal emission analysis, and the gas chromatographic peaks were identified by mass spectrometry. An analytical method was developed for the separation and determination of the dimedone adducts of aliphatic aldehydes by gas chromatography using capillary columns.

The Effect of Molecular Structure upon the Response of the Flame Ionization Detector

SummaryIt is known that the response of the FID is proportional to the number of carbon atoms in hydrocarbon molecules. If there is a heteroatom in the molecule, the response of the FID decreases. It is possible to calculate the sensitivity to any organic molecule if the signal-decreasing effect of a heteroatom or functional group is known. The sensitivity of a detector to an organic molecule containing heteroatoms is referenced to normal hydrocarbons by means of the effective carbon-atom number (ECN). Several authors have dealt with the determination ofECN values of different molecules and the effective carbon-atom number increment (ECNinc) values for different functional groups and heteroatoms. In our previous work [1]ECNinc values of several components were studied for homologous series. In this study we have investigated the effects of molecule structure upon ECN values by comparing theECNinc of functional groups which are attached to molecules of different structure.

The Determination of GC -MS Relative Molar Responses of Some n-Alkanes and their Halogenated Analogs

The dependence of relative response factors on the carbon atom number related to naphthalene has been investigated in homologous series by using gas chromatography-mass spectrometry. Relative responses of some straight chain aliphatic n-alkanes and their halogenated derivatives (chlorine, bromine and iodine) were compared in the experiments. Linear correlations were found between the molecular structures; i.e., the carbon atom number and relative molar response in current homologous series. In conclusion, mass spectrometric detection combined with gas chromatography was less sensitive to n-alkanes than to their derivatives containing a chlorine, bromine or iodine atom. After n-alkanes, mass spectrometric responses increase in the order of 1-chloroalkanes, 1-bromoalkanes and 1-iodoalkanes. These results are in accordance with electron ionization cross section data for n-alkyl-derivatives. The relative molar responses of the individual CH(2) groups are between 0.171 and 0.178 in the homologous series. The increments of chlorine, bromine and iodine atoms to the relative molar responses are 0.081, 0.141 and 0.492, respectively. Based on these results, the addivity rule is valid for both halogen atoms and CH(2) groups in the case of mono-substituted n-haloalkanes. The results of this study show a significant departure from the additivity rule in the case of polyhalogenated alkanes and alkenes. However, the relative molar response can be calculated by means of simultaneously measuring other compounds. Further study is needed about how to influence the relative molar responses as a function of various experimental parameters.

Effects of Experimental Conditions on the Determination of the Effective Carbon Number

SummaryThe response of the flame ionization detector (FID) is proportional to the carbon number of hydrocarbon molecules; however, heteroatoms attached to the carbon chain can decrease the detectors response. Sternberg was the first who determined the effective carbon number increments (ECNinc), which show how different atoms contribute to the response of a molecule as a whole. If the extent of the contributions of different atoms or functional groups to the FID response of a molecule is known, one could calculate the relative response of analytes not available as a pure, authentic standards. An accurate and reliable quantitative analysis requires an accurate determination ofECNinc.The effects and parameters influencing theECNinc value have to be examined. Stemberg determined the effects of the detector geometry and of the parameters to the response. However, we assume that other experimental conditions can indirectly also affect theECN contributions.In this study, the effects of the temperature of the injector, detector and column and of the injection modes were investigated. We compared theECN values obtained at different concentrations and measured them with different hydrocarbons as the intermal standards.

Asymmetric hydrogenation of prochiral and kinetic resolution of chiral cyclohexanone derivatives with Pd catalysts

This paper focuses on the investigation of the role of catalytic and molecular factors determining the optical yield in the enantioselective hydrogenation of C=C double bonds in prochiral unsaturated ketones and in the kinetic resolution of racemates of chiral cyclic ketones with proline mediated reductive alkylation. The hydrogenation of two unsaturated methyl cyclohexenones, and the kinetic resolution of two saturated methyl cyclohexanones with proline were studied with different Pd catalysts. The aim was to find out the effects of catalyst modifiers and chiral auxiliary, beside that of the structure and the degree of substitution of the substrates on the stereochemical outcome and yield of these reactions.

CnH2nCl+ ion formation in electron impact MS conditions: A theoretical study

The mass spectral fragmentation of different 1-chloroalkanes (of the 1-chlorohexane-1-chlorooctadecane series) has been investigated, quantifying the relative abundance of the fragment ions. The base peak is dominantly at m/z 91, 93 in each investigated case, although with the increasing chain length, its contribution to the total ion current exhibits some reduction. Among the possible fragmentation products, the five-membered chloronium containing ring is the most stable as measured by an isodesmic reaction, although the six-and seven-membered rings exhibit only slightly reduced stability. The most stable structure of the 1-chlorohexane radical cation has a hydrogen bonded structure with the involvement of chlorine and the HC(δ), pre-forming the five-membered cationic ring. Accordingly, among the reactions leading to alkyl (or H) radical and a chloronium containing ring, this transition structure has the lowest energy, providing explanation for the experimental observations.

Analysis of internal filling gas of small-sized halogen lamps by gas chromatography

Abstract The internal filling gas composition of small-sized (H-3) tungsten—halogen incandescent lamps was studied. An appropriate destructive sampling device was constructed and used to interface the sample source and the gas chromatograph. A high-resolution, sensitive chromatographic method was devised out for the determination of the main components in the lamp atmosphere and some of the impurities. It was found that decomposition products are formed inside the H-3 lamps during use. Their concentration as a function of the burn time can be followed by the proposed technique. The sampler interface with a Hewlett-Packard Model 5890A gas chromatograph and the isothermal elution method are described in detail. The concentration—burn time dependence gives information about the ageing process.

WO3–EDA hybrid nanoplates and nanowires: synthesis, characterization, formation mechanism and thermal decomposition

Previously the WO3–EDA hybrid material was obtained only from solvothermal reactions. In this study this hybrid was prepared by two novel methods: a solid–gas phase heterogeneous reaction, and a wet chemical process. In the case of the solid–gas phase reaction the effects of the composition, crystal structure, and the particle size of the WO3 powder and the presence of H2O vapor were studied, while in the case of the wet chemical process the effect of the solvent was investigated. The structure, composition, morphology and thermal decomposition of the as-prepared WO3–EDA hybrid were investigated by XRD, FTIR, solid-state NMR, elemental analysis, SEM, TEM and TG/DTA-MS measurements. In addition, its catalytic activity was tested in a Knoevenagel condensation model reaction. Based on the results the WO3–EDA empiric formula was proposed to replace the current WOx–EDA formula. From the solid–gas phase reaction WO3–EDA nanoplates were obtained for the first time. Furthermore, a new formation mechanism was proposed for the solid–gas phase formation of this hybrid material. The thermal decomposition of the hybrid resulted m-WO3 in air, and an amorphous tungsten oxide phase in nitrogen. During annealing, the evolved EDA transformed into a series of heterocyclic aromatic compounds in both atmospheres. The as-prepared hybrids had the same catalytic properties as the hybrids obtained previously from the solvothermal reactions.

Relative molar responses of some compounds containing oxygen and nitrogen in GC–MS

Relative molar responses (RMRs) of some straight-chain aliphatic alkanes, ketones, aldehydes, alcohols, carboxylic acids, primary amines, aniline, and nitrobenzene derivatives were investigated related to naphthalene. Most of the respective compounds have not been investigated yet due to their high polarity or high boiling point. The earlier cross section data for oxygenated compounds were changed to RMRs which are more utilizable from an analytical aspect. A linear correlation was found between the RMRs and the carbon atom numbers in primary amines. In the cases of aniline and nitrobenzene derivatives the RMRs were also determined; however, no functional relationship was found. The measurement conditions, i.e., the type of column affect the apparent RMRs of aliphatic primary amines. A midpolar column having a higher maximum operating temperature provides a more sensitive apparent RMR (Rtx-1701) than the basic polar column having a lower maximum temperature (Stabilwax-DB), because a high temperature allows setting a higher injector temperature and a higher amount of compound can reach the ion source. Knowing correlations the quantitative analysis passes into easier and fewer reference materials are needed to investigate a sample having many components, because the sensitivities can be determined from the correlations studied in this paper. This is also valid for aromatic compounds, even though no functional relationship exists.