Analysis of light hydrocarbons in marine sediments by headspace technique: Optimization using design of experiments

Abstract

Headspace technique is a common method to analyze light hydrocarbons in deep marine sediments. The use of an automatic headspace sampler instead of a manual injection is the guarantee for a better repeatability and furthermore it is less time consuming. But to increase the sensitivity and therefore, to achieve a better detection limit, it is necessary to optimize the automatic headspace sampler parameters. The theory of design of experiments was applied here by studying them. As a response, methane, which is an important gas in marine sediments, was chosen for its short analysis time. Regarding the parameters for automatic headspace sampler, eight variables were selected and then, a screening of them was carried out with a fractional factorial design to determine the influential factors. Finally, optimization was conducted with four factors: Sample Loop Fill time ( t slf), Oven temperature ( T° o), Vial Pressurization time ( t vp) and Vial pressure ( P v). They were modeled with a Doehlert experimental design. Then, the model was validated by a conventional statistical test (analysis of variance) and the optimum has been found and checked by three experiments. Results on light hydrocarbons measured in sediments from the Congo–Angola Basin are given, as an example.