Investigation of matrix-free generation of methyl chloride as a reference material

Abstract

This article describes the results of investigating the use of fused-silica fibers with chemically-modified surfaces as a source of matrix-free reference material – methyl chloride in an inert gas. The analyte is generated in the process of thermal decomposition of (immobilized) compounds bonded to the surface. Prior to chemical modification, the fibers were coated with a thin layer of polyimide to improve their mechanical strength, followed by a metal film (Al or Ti) to obtain active sites; hydroxyl groups required for chemical modification are present on the surface because both metals are readily oxidized in air and they form a protective layer of oxide. Some fibers under study, available commercially, were coated with only a thin film of aluminum. Three different thicknesses of metal film were used for the fused-silica fibers coated with thin polyimide film. Fibers with different diameters and thicknesses of metal film were used for the fibers coated with only the layer of aluminum. For the fibers of the first type, reproducible amounts of CH 3Cl released per unit length of the fiber were obtained, irrespective of the kind of metal and the layer thickness: 0.111 ± 0.032 ng/cm for the SPME device and 1.676 ± 0.014 ng/cm for the thermal desorber. For the fibers of the second type, the amounts of CH 3Cl released were also reproducible and, depending on the glass-fiber parameters, were: 1.408 ± 0.015 ng/cm, 1.583 ± 0.040 ng/cm and 1.993 ± 0.040 ng/cm.