Evaluation of split/splitless operation and rapid heating of a multi-bed sorption trap used for gas chromatography analysis of large-volume air samples

Abstract

The effects of split-flow operation and rapid trap heating on injection-plug widths from an electrically heated, microscale, multibed sorption trap were evaluated. The sorption trap has been designed to quantitatively collect volatile organic compounds from large-volume vapor samples and inject them into a gas chromatograph. Previous trap designs resulted in injection-plug widths of typically a second or more, and this significantly degraded chromatographic resolution, particularly for early-eluting sample components and for high-speed separations. Injection-plug widths are determined by the heating rate of the trap during sample desorption and the volumetric flow rate of carrier gas through the trap. The effects of the heating rate of the trap and carrier gas velocity through the trap on the injection-plug widths of pentane, octane, and undecane were studied. Carrier gas velocity through the trap was increased by splitting the flow coming from the trap between the column and a vent. This decreases transport time from the trap to the column, and thus decreases injection-plug widths. The heating rate for the trap was increased by increasing the applied voltage in the range from 4 to 30 V. Increasing the heating rate decreases the time required to desorb the analytes from the sorbent bed, thus decreasing injection-plug width. Injection-plug widths as small as 89, 210, and 520 ms were obtained in the split mode with very fast heating rates for n-pentane, noctane, and n-undecane, respectively. The effect of split ratio on resolving power, peak height, and peak width was also evaluated.

Characterization of a high-performance portable GC with a chemiresistor array detector

“…A splitinjection capability was incorporated in this prototype to reduce injection plug width by venting a portion of the desorbed flow stream. 15,39 The first separation column (4.5-m long, 0.25-mm i.d.) contains a wall-bonded polydimethylsiloxane stationary phase (DB-1, 0.5-mm thickness, Agilent, Wilmington, DE) and the second column, which has the same dimensions as the first, contains a wall-bonded polytrifluoropropylmethylsiloxane phase (RTX-200, 0.25-mm thickness, Restek, Bellefonte, PA).…”

“…Contributions to band broadening from adsorbent preconcentrators similar to that used here have been studied previously. 15,19,34,39 Rapid heating rates and high flow rates through a PCI serve to minimize broadening, but analyte volatility is also an important co-factor. Band broadening from the type of microsensor array used here has not been studied systematically, 15 and could arise from the finite volume of the detector cell as well as the rates of sorption and desorption of eluting vapors into and out of the interface layers on the sensors.…”

“…36 Since the heating rate of the PCI could not be increased further, only the carrier gas flow rate through the PCI was explored as a means of reducing the injection band width. Split-flow injection has been shown to improve resolution in portable and micro-scale GCs, 15,39 at the expense of sensitivity. However, the former is often the more important factor in complex mixture analysis.…”

“…30 This article presents a thorough characterization of the second-generation instrument. Since the topics of preconcentrator design and pressuretuned separations have been covered in previous articles, 30,[34][35][36]39 they are not emphasized here. Rather, an emphasis is placed on the influence of changes in flow rate and temperature on the performance of the CR array.…”

Application of Advanced Sensor Technology to DoD Soil Vapor Intrusion Problems

“…Thus, it is desirable to maximize the rate at which samples captured on the µF are desorbed and injected onto the separation column. In general, this calls for rapid heating and high flow rates through the µF Zellers, 2001 &Whiting and Sacks, 2006;Sanchez and Sacks, 2003).…”