Basics of LPGC (Low pressure GC/Vacuum GC)

Fast gas chromatography (GC) using mass spectrometry (MS) has always been challenging as we have to use a column with sufficient restriction under vacuum-outlet conditions. Short 0.10mm columns will work, but are practically challenging to work with in regards to injection and capacity.

In 2001 a new concept was presented for speeding up GC-MS analysis using short 0.53mm capillary columns (directly connected at the MS inlet) connected to a restriction column at the inlet, enabling a high vacuum inside the 0.53mm analytical column. Technique is known as LPGC (Low Pressure Gas Chromatography) or sometimes called “Vacuum GC”.

Under the conditions created, very fast separations were performed as the optimal carrier gas velocity is a function of the actual pressure inside the capillary. Typically, 3x shorter run times are obtained. We trade some efficiency for speed and robustness. Since a MS detector is used, no full chromatographic separation is required. This technique was immediately adopted by Lehotay around 2003 for fast pesticide screening in Quechers extracts of food samples. Together with Lehotay, an optimized pre-assembled robust column for LPGC for fastest possible pesticide screening was developed and will be discussed in detail.

In this tutorial the basics of LPGC are discussed and the impact it has on the chromatography of - for example - pesticides in food. The technique can be applied for virtually all GC/MS analysis, providing there are no isobars that need to be separated that have more than 100.000 theoretical plates.