Programmable smart fast gas chromatograph and open probe controller.

ABSTRACT

Today, labs that carry out chemical analyses for regulation, food safety, health, forensics, or even security purposes are looking for ways to accelerate the analytical process. Slow procedures are costly because the necessary instruments are expensive and require maintenance and a highly trained staff to operate them. One of the more ubiquitous instruments in such labs is a Gas Chromatograph (GC), which accepts a solution and outputs each of the compounds within it in a gaseous form, one by one to be further analyzed and identified, usually by a Mass Spectrometer (MS). This separation process in a GC can be rather time-consuming, partly due to the slow heating and cooling of the GC column through which the compounds move, which happens inside a box-shaped oven. This paper describes a controller developed for a unique Open Probe Fast GC instrument that enables, among other things, high-speed and controlled heating and cooling of a gas-carrying capillary transfer line. Fast heating is achieved by precisely controlling the electrical current flowing through the small inner-diameter steel tube through which the GC column passes. The fast cooling occurs by exposing the low-mass heated tube to room temperature, along with the assistance of a simple fan that carries the heated air away. This technology also supports control of other system parts, including a unique quick sampling device called an Open Probe that allows for an even faster analysis cycle. Our design is based entirely on a digital signal processor (DSP) and digital control. The use of pulse width modulation (PWM) control enables a compact and efficient system.