Aliphatic and Aromatic TPH – A New Dimension

For years, the separation of Aliphatic and Aromatic TPH fractions (as in TPH CWG analysis) has involved the use of a physical bench top separation technique such as Solid Phase Extraction (SPE).

After initial solvent extraction of samples, in traditional SPE the extract is passed onto an SPE cartridge and the aliphatic fraction firstly eluted with solvent, then the aromatic, generating two individual sample extracts, which are each then analysed by Gas Chromatography (GC). Using a single column, carbon species are then separated in accordance with their boiling point and a traditional chromatogram produced.

Diesel chromatogram by single dimension GC separation

Such techniques have a number of limitations. They tend to be very labour intensive, separation is prone to cross contamination or ‘breakthrough’, due to inherent losses during preparation, sample recovery can be poor and the number of stages involved allows potential for error to be introduced.

Scientific Analysis Laboratories has recently helped pioneer the development of a system that negates the need for such physical separation of fractions prior to analysis and allows the separation to occur in situ, within the instrument.

This GC-GC system utilises two columns aligned in series. The first, a Non Polar column, is able to separate carbon species based on their boiling point. A modulator then passes the output of the first column into a second, Polar column. Here, species are separated due to their polarity.

The resulting chromatogram depicts the separation of carbon species over 2 dimensions.

Diesel chromatogram by 2 dimensional GC separation

This technique has a number of distinct advantages over SPE;

As there is no physical split, no losses occur and a 100% split is achieved
No ‘breakthrough’ can occur and variances in SPE cartridges and their conditioning are a thing of the past, ensuring that data is more consistent, reliable and reproducible.
Multi stage, laborious preparation steps are negated

In line with our continuous improvement programme, SAL have invested in a number of these systems in an effort to provide the best quality data in the time scales required by our clients.

Please contact your local SAL office to learn more about other exciting new developments.