Quantification of Middle Distillates

ASG 2253 GC×GC-TOFMS
ASG 2502 GC×GC-FID
ASG 2901 GC×GC-FID

Comprehensive two-dimensional gaschromatography (GCxGC) provides an enormously enhanced selectivity compared to conventional gaschromatography. By the hyphenation of capillary columns of different polarity, it is possible to separate complex mixtures into single components.
The heart of the two-dimensional separation is the so-called modulator, which is located between the first and second column. The function of the modulator is to accumulate eluents of the first column, which are then refocused in small “packages” and afterwards “injected” into the second column for further separation.
Thermal modulation is achieved by alternating freezing and releasing of compounds by Cold- and Hot-Jets. Alternatively, the carrier gas flow can be regulated periodically (flow modulation). Structure and functionality are displayed schematically in following figure.

The following figure shows a representative two-dimensional chromatogram of common diesel fuel according to EN 590, as well as the results of the data evaluation and quantification. The separation was achieved by the application of a so-called “reversed-phase” column combination, consisting of a 50% phenylsubstituted column as 1^st dimension and a 100% polydimethylsiloxane column as 2^nd dimension.

HVO and XtL fuels are characterized especially by their low content of aromatic compounds compared to conventional middle distillates. The application of GCxGC-FID is particularly suitable for the analysis of these small amount with a limit of detection of 0.05% (m/m).

Additional methods are available in form of high-temperature GCxGC-FID and -MS, respectively (ASG 2501 and 2221), and are applied especially for samples that strongly diverge from common middle distillates, e.g. by a high boiling range.