At-column heating and a resistively heated, liquid-cooled thermal modulator for a low-resource bench-top GC×GC

Abstract

A transportable GC x GC instrument is under development for on-site applications that would benefit from the enhanced resolution and powers of detection, which can be achieved by this method. In the present study, a low-resource GC x GC instrument using an electrically heated and liquid-cooled single-stage thermal modulator that requires no cryogenic materials is evaluated. The instrument also uses at-column heating, thus eliminating the need for a convection oven to house the two columns. The stainless-steel modulator tube is coated with PDMS, which can be heated to 350 degrees C for sample injection into the second-dimension column. The modulator is cooled to -30 degrees C by a 100 mL/min flow of PEG by means of a commercial liquid chiller and a small recirculating pump. Resistive heating of the modulator tube is provided by a programmable power supply, which uses a voltage program that results in increasing modulator temperature during an analysis. This, together with more rapid cooling by the use of a liquid cooling medium, results in reduced solute breakthrough following each heating cycle as the modulator cools to a temperature where quantitative trapping resumes. As a result, modulated peak widths at half-height of less than 40 ms are observed. Design and performance details are presented along with chromatograms of gasoline and an essential oil sample.

Thermal Desorption Comprehensive Two-Dimensional Gas Chromatography: An Improved Instrument for In-Situ Speciated Measurements of Organic Aerosols

“…The most commonly used modulators in atmospheric chemistry have been cryogenic and valvebased modulators (Hamilton 2010). However, because robustness, simplicity, and low operating costs are attractive features, recent work has focused on the development of improved versions of this type of modulator (Libardoni et al 2005(Libardoni et al , 2006(Libardoni et al , 2010Panić et al 2011). Successful single-stage modulation has been reported using recirculated cold air (−30…”

“…• C) (Libardoni et al 2006) to rapidly cool the trapping capillary between heat pulses, producing very narrow peaks (FWHM < 40 ms) for analytes with boiling points of up to the equivalent of n-eicosane (C 20 H 42 ; bp = 344…”

“…As the GC run progresses and the oven temperatures increases, the trapped components become less volatile and higher desorption temperatures are desirable to minimize band broadening during injection onto the second column. Libardoni et al (2006) ramped the discharge voltage of the heating pulse to increase the desorption rate of higher molecular weight analytes and maintain sharp injections onto the second column. Therefore, ideally, the trapping and desorption temperatures of the most efficient modulator should track changes in the GC oven temperature.…”

Comprehensive two-dimensional gas chromatographic separations with a temperature programmed microfabricated thermal modulator

“…Several investigators have reported on ways to address this problem by gradually ramping the modulator temperature as a separation proceeds [19,[26][27][28]. For example, the Marriott group addressed this problem effectively with their longitudinally modulated cryogenic system (LMCS), in which a moveable sleeve around a section of capillary column is cooled with a flow of cryogenic fluid [19].…”

The Importance of Detector Acquisition Rate in Comprehensive Two-Dimensional Gas Chromatography (GC×GC)

“…Each type of modulator has specific advantages and applications; however, for this study only thermal modulation was used. Thermal modulators use differences in temperature to change the retention factor (k value) of the trapped compound(s) during the modulation process (5,6). Column cooling essentially "traps" components in the modulator prior to a pulse of heat to release the components.…”