A pinch-valve interface for automated sampling and monitoring of dynamic processes by gas chromatography-mass spectrometry†
Gas chromatography (GC) is frequently used in qualitative and quantitative analysis of volatile organic molecules. In its most common embodiment, samples are prepared in the laboratory, and injected into the capillary column using an autosampler. Analytes are separated, and detected by one of several available detection systems, including mass spectrometry (MS). However, this mode of operation is not convenient when monitoring dynamic chemical systems – for example, reaction mixtures. Here we present a facile approach for automated sampling, and subsequent introduction of samples to a GC apparatus in order to enable monitoring of dynamic chemical processes in real time. The proposed system incorporates two pinch valves, a peristaltic pump, a thermoshaker, and an electronic control unit (Raspberry Pi microcomputer) with several relays. The device facilitates dosing small volumes of liquid samples to the injection port of a commercial GC-MS apparatus. A program in C language controls the operation of the pump (on/off, direction of flow) and actuation of the pinch valves, and it initiates GC-MS runs. The system has been characterised with artificial samples, and successfully used in the monitoring of transesterification reactions catalysed by single microbeads containing immobilised lipase, as well as in the monitoring of the extraction of natural products from plant tissue samples. We believe that – following further improvements – this automated approach may be adapted for monitoring industrial processes and environmental analysis.