Automated monitoring of organic trace components in water : I. Continuous flow extraction together with on-line capillary gas chromatography

Abstract

A system for automated monitoring of volatile organic trace compounds in water is described. The water is continuously extracted in a fused-silica capillary tube after flow injection of an immiscible solvent. Separation of the phases is accomplished with a porous PTFE membrane separator. The extract flows through a fused-silica sample loop, connected to a fused-silica capillary column or pre-column. The system operation is controlled by a programmable timer, which allows unattended analysis with regular time intervals. For evaluation of the system, dilute water solutions of aromatic and aliphatic hydrocarbons as well as water samples contaminated with trace amounts of a naphtha fraction were employed. Extraction was performed with n-pentane. The results were practically identical to those obtained from batch extractions carried out under comparable conditions. However, a better reproducibility was obtained with the flow extraction procedure. The on-column injection of large sample volumes (150 μ) permitted analyses at the ppt level, as demonstrated with a sample of continuously extracted waste-water from a sewage plant. Significant adsorption of the trace components can occur on surfaces that are not brought into contact with the extractant. It is suggested that only a short length of fused-silica capillary tubing be used as a connection between the sample and the segmenting device.