Automation of the GC/MS analysis of mineral oil contaminations in water

An automation of the sample preparation and analysis of mineral oil contaminations in water was developed. The automated sample preparation was carried out according to ISO/DIS 9377-4 [1]. The standard is applicable to the determination of hydrocarbons in the boiling range of n-decane (n-C10) up to n-tetracontane (n-C40) by GC. Extraction of the sample and clean-up of the extract were performed by an autosampler with a movable head which is capable of carrying different syringes for gas and liquid handling. A GC/MS-system with a programmed temperature vaporizing (PTV) injector including the possibility of large volume injections (LVI) was employed for the analysis. The recovery of analytes was 101.8%, the repeatability 2.9% relative standard deviation (RSD). The linear range covered 0.3 to 40 mg/L oil but may be larger since no higher concentrations were measured. With an FID, being the detector of choice mentioned in the standard, it should be possible to achieve at least four orders of magnitude in the linear range. The limit of determination was found to be 0.3-0.4 mg/L, the limit of detection 0.1-0.2 mg/L [2]. Measurements of spiked deionized, bidistilled water and spiked water from a lake confirmed the accuracy of the analysis. Due to automation and miniaturization of the analysis it is possible to economize time and chemicals without loss of precision and accuracy.