SummaryThis paper deals with the separation of alkanes, naphthenes, and aromatic compounds in naphtha and reformate, on a newly developed apolar high resolution GC column. The selectivity of this apolar phase has been compared with those of squalane, DB-1, and SE-30. A total of 95 hydrocarbons were reliably identified, mostly by GC-MS. Repeated measurements of Kovhts retention indices are presented as evidence for the reproducible manufacture of fused silica columns coated with this phase. This paper reports results obtained using a new thermally stable, chemically bonded and cross-linked apolar liquid phase. The polarity of the new phase approaches that of squalane and is distinctly lower than that of poly(dimethylsi1oxanes). Its unique selectivity enables, e.g., the analysis of hydrocarbons in the range c4-c 1 1.
Materials and Methods 1 IntroductionFor many years it has been known that squalane exhibits the lowest polarity of all liquid stationary phases. Many authors have investigated retention behavior on this phase. This phase has been especially popular in petrochemistry for the analysis of hydrocarbon mixtures such as gasoline. Hydrocarbons are eluted in order of decreasing vapor pressure at the column temperature, i.e. generally in order of increasing boiling point. Thus, light hydrocarbon analysis has been performed successfully on fused silica columns coated with squalane or slightly polar bonded and cross-linked poly(dimethylsi1oxane) phases [ 1-31.Unfortunately, squalane has some disadvantages. Firstly, the phase does not wet fused silica (incompatible surface tension) or be chemically bonded to the column wall; this results in mechanically unstable films and short lifetime, and the columns cannot be rinsed by solvents. Secondly, the maximum isothermal operating temperature (MAOT) is limited to 90 "C, which means that it is practically impossible to analyze hydrocarbons larger than C9. Column bleed is intolerably high, column lifetimes are short, and GC-MS detection of trace quantities between 70 and 90 "C cannot be recommended. Thirdly, it ib not possible to produce thick film columns becausc droplets are formed on the column walls, which results in very low plate numbers. The more stable but, to a certain degree, also more polar poly(dimethylsi1oxane) phases, on the other hand, have distinctly different selectivity which sometimes results in coelution.
Chemicals and GasesNaphtha and reformate were purchased from Leuna-Werke GmbH, Germany; alkanes, naphthenes, and aromatic compounds as reference probes for identification were from Polyscience Corporation, Niles, Illinois, USA, and the McReynolds probes were from Fluka Chemie AG, Buchs, Switzerland. The carrier gases helium and hydrogen (high grade > 99.9995 %) were purchased from Linde AG, Unterschleissheim, Germany.
GC Capillary ColumnThe CP-Sil2 CB column was recently developed by Chrompack International B.V., The Netherlands. The phase is a chemically bonded and cross-linked (4 70) silicon-containing a high molecular weight (> 10000) hydrocarbon s...
