Dependence of retention indices of alkylbenzenes on their molecular structure

Speciation of alkylated dibenzothiophenes through correlation of structure and gas chromatographic retention indexes

The gas chromatographic (GC) speciation of polycyclic aromatic sulfur heterocycles (PASH) in deeply desulfurized fuels is difficult without recourse to authentic standard compounds. Here we investigate the GC retention indexes for 30 alkylated dibenzothiophenes on two methylphenylsiloxane stationary phases of different selectivity (5% and 50% phenyl groups) with a view to avoid the synthesis of all congeners. The influence of the substitution pattern on the retention indexes is discussed. With the measured data it is possible to carry out a multiple linear regression (MLR) to calculate parameters for predicting the retention indexes of unknown polymethylated isomers based only on their structural features. Nine trimethyldibenzothiophene in a synthesis product are identified through their retention indexes. The retention indexes for a total of 43 alkyldibenzothiophenes are listed.

Sensitivity of the methylbenzenes and chlorobenzenes retention index to column temperature, stationary phase polarity, and number and chemical nature of substituents

Retention indices of methylbenzenes and chlorobenzenes on two fused silica capillary columns, HP-5 (diphenylsiloxane 5% diphenyldimethylsiloxane) and ZB-WAX (polyethylene glycol), have been calculated at various isothermal temperatures and compared with literature data. The retention index temperature effect was studied for each solute, finding greater retention index the higher the column temperature. A comparison between the straight line fit and the fit to the recently proposed equation I = A + B/T +C ln T was carried out. The effect of the stationary phase polarity on the retention index was checked. In general, a greater retention index was found for the more polar stationary phase. The retention indices of the chlorobenzenes are greater than the retention indices of the methylbenzenes, irrespective of the stationary phase and the column temperature. In addition, the influence of the methyl/chlorine substitution on the benzene molecule was investigated at each temperature. The retention indices increased as the number of substituents (methyl/chlorine) increased. The retention index increments of methyl and chloro derivatives are also discussed, which permits to compare the effect of both, methyl or chlorine, chemical functions, for a fixed substituent number in the benzene molecule.

Prediction of gas chromatographic retention indices of polychlorinated dibenzothiophenes on non-polar columns

Polychlorodibenzothiophenes (PCDTs) have been found in several kinds of environmental samples. The lack of reference compounds has meant that very little is known about their gas chromatographic behavior. Here we discuss the retention of 19 authentic PCDTs and their sulfones on the widely used gas chromatographic stationary phases DB-5 and DB-5ms. The retention order is different from that of the polychlorodibenzofurans. The data generated allowed us to carry out a multiple linear regression to generate parameters for predicting the retention indices of unknown congeners based only on their structural features.