Automation of an analysis system with microvolume porous membrane sampling, capillary electrophoresis separation and contactless conductivity detection for near-real-time monitoring of traces of low-molecular-weight carboxylic acids in air

摘要

An automatic analysis system was designed by coupling a complete microvolume sampler based on a capillary membrane diffusion scrubber (CMDS) to capillary electrophoresis (CE) equipment with capacitively coupled contactless conductometric detection (C4D). The microliter capacity of the CMDS, matching with the nanoliter demands of the CE-C4D equipment, led to the design of an automated system with fluid management based on affordable and maintenance free aquarium pumps, pinch valves under computer control, a miniaturized CMDS-CE interface and a rugged CE equipment operated with hydrodynamic injection. As an application of the system, it was successfully demonstrated that formic acid and acetic acid in air can be quantitatively sampled together, with high pre-concentration ratio, and quantified at a frequency of 10 complete analyses per hour of unattended operation, but electrolyte renewal on a daily basis. Limits of detection of 1.2 μg m-3 for formic acid and 3.0 μg m-3 for acetic acid in air, were estimated with linear response over the usual concentration range of these analytes in the gas phase of the atmosphere.