No abstract

This study applies Ultrafast module-GC (UFM-GC) with direct resistively heated columns to routine analysis of a group of essential oils of differing complexities (chamomile, peppermint, rosemary and sage). Essential oils were analysed by conventional GC with conventional inner diameter (i.d.) columns (0.25 mm) of different lengths (5 and 25 m long) and by Fast GC and Ultrafast module-GC with narrow bore columns (0.1 mm i.d., 5 m long). Column performance were evaluated and compared through their Grob test, separation number and peak capacity. Ultrafast module-GC was successful in the qualitative and quantitative analysis of essential oils of different compositions with analysis times between 40 s and 2 min versus 20-60 min required by conventional GC. Critical pairs or groups of components were separated by carefully tuning selectivity of the stationary phase to compensate for loss of efficiency due to the use of short columns and high temperature rates. The Ultrafast module-GC results of peppermint e.o. analyses were also validated and compared to those obtained by conventional GC; by measuring precision over time (i.e. repeatability and intermediate precision) and accuracy. Ultrafast module-GC showed a good separation reproducibility affording reliable component identification through the relative retention times and quantitative determination through normalised peak areas. Accuracy data also showed that Ultrafast module-GC and conventional GC normalised areas and areas percentage were perfectly comparable.

The characterization of heavy petroleum fractions is essential for the design and improvement of cracking plants converting heavy feedstock into valuable "white" products. Conventional simulated distillation methods using packed columns are unsuitablefor this purposes, being limited to boiling points up to about 600OC. The method presented is able to cover a boiling points interval ranging from about 150°C up to around 800OC. It employs a short, nonpolar, highly thermostable capillary column routinely operated at temperatures around 430OC. The analytical system is based on a high temperatureversionof a fullyautoma-Dedicated to Professor Kurt Grob on his 65th birthday. tic, capillary dedicated gas chromatograph. The experimental data demonstrate that cold on-column injection is the sole sampling system suitable for such heavy compounds. The conversionof theretentiontimesinto boilingpoints, basedontheuseof low molecular weight polyethylenes, is extremely reliable, as demonstrated by the excellent retention time reproducibilities. The lower part (up to 550-600°C TBP) of the boiling point distribution curves of heavy petroleum fractionsobtained on capillary columns fits well with the corresponding distribution curves based on packed column data. For the petroleum fractionsfully eluted from the column the quantitative results obtained either using internal standards or by direct processing of the elution curves are in excellent agreement (less than 0.3 weight YO differences). The method has been applied to the determination of the true boiling points corresponding to short path vacuum distillation (DISTACT) cut points over 300OC. 0

No abstract

No abstract