Performance characteristics of a new prototype for a portable GC using ambient air as carrier gas for on‐site analysis

Abstract

The performance characteristics of a portable GC instrument requiring no compressed gas supplies and using relatively lightweight transportable components for the analysis of volatile organic components in large-volume air samples are described. To avoid the need for compressed gas tanks, ambient air is used as the carrier gas, and a vacuum pump is used to pull the carrier gas and injected samples through the wall-coated capillary column and a photoionization detector (PID). At-column heating is used eliminating the need for a conventional oven. The fused silica column is wrapped with heater wire and sensor wire so that heating is provided directly at the column. A PID is used since it requires no external gas supplies and has high sensitivity for many compounds of interest in environmental air monitoring. In order to achieve detection limits in the ppb range, an online multibed preconcentrator containing beds of graphitized carbons and carbon molecular sieves is used. After sample collection, the flow direction through the preconcentrator is reversed, and the sample is thermally desorbed directly into the column. Decomposition of sensitive compounds during desorption is greater with air as the carrier gas than with hydrogen.

The effect of cold trap adsorbents on the gas chromatographic analysis of ambient VOCs under Peltier cooling conditions

“…Hence, selection of any single adsorbent might not be sufficient for the collection of multiple analytes with a broad volatility range. This problem can be resolved by the application of multibed adsorption tubes, packed in order of increasing sorbent strength to cover diverse analytes over a broad range of volatility and polarity [15,16]. Although limited under ambient conditions, a comprehensive review of different adsorbents available for the adsorptive enrichment and thermal desorption in ambient air analysis has been studied by Dettmer and Engewald [17].…”

“…[18]. It is well known that Carbopack C (a graphitized carbon blacks (GCB) with specific surface area (SSA) l10 m 2 /g) is a relatively weak adsorbent for collecting heavy VOCs (e. g., C 8 -C 20 ), while Carbopack B (GCB with SSA l100 m 2 /g) is a moderately strong adsorbent for collecting low to medium range VOCs (C 4 -C 8 ) [16]. The CT (II) was distinguished by the same mass ratio of Carbopack B (60/80 mesh) and Carboxen 1000 (60/80 mesh).…”

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

“…Figure 1 shows a diagram of the multibed trap, the separation column and the associated plumbing. Design features of the multibed trap have been described in detail [10,11]. The trap was similar to a design reported by Lu and Zellers [12,13].…”

“…This prevents the highest boiling point components in the sample from ever contacting the strongest beds. With this arrangement, quantitative desorption is obtained with no memory effects [10,11].…”

“…Injection-plug characteristics of this multibed trap were studied by Sanchez and Sacks [10,11]. Thermal desorption was accomplished by the direct resistive heating of the metal trap tube.…”