Presentation Profile
Ultrafast Desorbing Concentrators for Gas Chromatography
Currently Scheduled: 10/15/2019 - 11:15 AM - 11:45 AM
Room: Exhibit Hall Room A4
Main Author
Dale Ashworth - VICI Valco Instruments
- Matias Hochman - VICI Valco Instruments
- Huamin Cai - VICI Valco Instruments
Abstract:
In gas chromatography, using a trap to concentrate the sample is one of the most common methods to improve detectable limits. To use this method, the trap should be able to heat very quickly in order to release the most consolidated and narrow injection to the head of the column. The two most common desorbing methods for a concentrating trap are direct heat and indirect heat. The direct heat method applies an electrical current directly through the traps' conductive metallic tube. By regulating current and/or voltage, a ballistic temperature ramp can be achieved through the trap. The advantages of the method are simplicity and faster heating. However, the trap temperature is not well controlled and some trial and error will be needed to determine the heating power. Additional challenges to this method are an inability to tightly control the trap temperature, either during absorption or desorption. As well, the trap is affected by many other factors such as the starting temperature, environment temperature, and air flow to list a few. These influences increase the variables that, if not controlled, result in poor precision in the sampling method. The indirect method uses a wire, cartridge, or pad heater on or around trap tube; the trap is heated indirectly by the heating apparatus. While this method is a bit more elegant than the brutally simple direct method, the indirect can use a feedback circuit to accurately control temperature, and it can be applied to nonconductive materials used for some traps, such as fused silica or glass. There are, however, disadvantages that come with indirect heating; one is the limited heating rate due to concentrator mass and controls that cannot accurately control temperature overshoot on fast ramping applications. So even if the ramping rate of indirectly heated concentrator can be increased very quickly, it may overshoot by a significant amount, and the larger the trap, the greater the lag (differential) between the heat being applied and the actual trap temperature. This presentation will detail this unique heating technology developed by Valco, which combines benefits of both direct and indirect heating with temperature sensing being done through the heater. With electrical heating and sensor combined, it is guaranteed to reduce lag by reducing moving mass, and because of the advanced control algorithm overshoot is virtually eliminated. This technique has been successfully applied on preconcentrators as well as GC columns, cold on-column injectors, programmable temperature vaporizers, retention gaps, transfer lines, and detectors. This technology has also been applied in both direct heated and indirect heated applications. The indirect method can be applied on metalic tube, fused silica or glass tube traps. The direct method requires a conductive tube or surface in order to function. Whether using direct or indirect heating methods, highly accurate and precise heating profiles of up to 2500°C/min from 50°C to 300°C with lag of <8°C and overshot < 5°C can be achieved. In addition, the same temperature controller and heating method can maintain control and ballistic rates from sub-ambient conditions (down to <-175°C) up to 400°C.
