The Analysis of Contaminants in Liquefied Gases by Gas Chromatography

Contaminants in liquefied gases are an analytical challenge. Contaminants are often high boiling or unstable components and their high molecular weight relative to the lighter matrix complicates the introduction of a representative sample into a gas chromatograph. The use of vaporisers, injection valves, and transfer lines is not recommended due to the effects of discrimination, adsorption, and fractionation of these high boiling components during the sample introduction process.

Current standardised test methods are not direct injection GC based, and determine dissolved high molecular weight residue by evaporating large volumes of the liquid sample, boiling off the light fraction, and thereby isolating the so called residue. This is then examined for volume or weight, visually inspected, or dissolved in a solvent and injected into a gas chromatograph. These methods are time consuming, have poor precision, and present a health and safety risk.

An alternative gas chromatographic method which features representative liquid phase injection is now available with the development of a new type of GC injector introduced by Da Vinci Europe laboratory solutions, an injector referred to as the Liquefied Gas Injector or LGI. An ASTM standard method for oily residue in LPG (ASTM D7756-11) based on direct on-column injection has recently been balloted and approved and will be available for distribution in December 2011. The LGI complies with this new method.