Effects of trapping temperature and film thickness in purge and trap with whole column cryotrapping on fused silica columns

Abstract

SummaryThe effects of trapping temperature and column film thickness were investigated with respect to their ability to promote effective cryofocusing on fused silica capillary columns. The study was a further development of the purge and trap with whole column cryotrapping (P&T/WCC) method. The rates at which compounds could be thermally desorbed from a P&T unit and transferred to a column (with zero split) were first examined. A near quantitative transfer of the desorbable analytes was obtained with a 4 min, 18OoC, 20 mL/min desorption. The compounds tested included naphthalene. Columns with film thicknesses from 0.1 2 to 3.0 pm were then investigated in P&T/ WCC analyses with WCC temperatures ranging from -80 to OOC. Thetrapping tookplacefrom a transfer linegas stream initially at 175OC. The volatilities of the compounds examined varied from that of 1,l -dichloroetheneto 111,2,2-tetrachloroethane. A higher film thickness was found to ease the WCC temperature requirements. Within each column type, the warmest WCC temperatures which allowed good cryotrapping with no significant increases in peak width were: 0.25 pm, -7OOC; 1.0 pm, -5OOC; 3.0 pm, -2OOC. In addition to being quantitative, the trapping provided good chromatography.

Volatilizable Biogenic Organic Compounds (VBOCs) with two dimensional Gas Chromatography-Time of Flight Mass Spectrometry (GC <b>×</b> GC-TOFMS): sampling methods, VBOC complexity, and chromatographic retention data

“…"Whole-air" sampling with canisters or bags provides an alternative to ATD cartridges and SPME fibers as a means to collect and transport sample analytes to a conventional laboratory for analysis. Whole air in a canister or bag can be aliquotted with a sample loop, cryofocused (e.g., at −150 • C on a trap containing 60/80 mesh glass beads as in method TO-14; US EPA, 1999a), sampled using ATD (Pressley et al, 2004) or SPME (Bouvier-Brown et al, 2007), or cryofocussed directly on the GC column (Pankow, 1986). For canisters, inert internal surfaces are important, and both Summa-polished TM stainless steel and Silcosteel TM canisters are used (US EPA, 1999a,b).…”

Determination of volatile compounds in water by purging directly to a capillary column with whole column cryotrapping

“…The first four compounds to elute (1,1-dichloroethane, dichloromethane, 1,1-dichloroethene, and chloroform) exhibited peak widths at peak base of 17,13,13, and 10 s, respectively. The remaining purgeable A compounds were much sharper with peak widths of ~5-7 s. Work in our laboratory (8,9,21) has indicated that relatively small changes in the WCC temperature can greatly improve chromatographic focusing on capillary columns. Thus, when a WCC temperature of -50 °C was tried, all of the peaks sharpened to widths in the 5-7-s range.…”

“…With 0.25-0.32 mm i.d. capillary columns, quantitative and well-focused trapping is obtained for compounds such as 1,1-dichloroethene and methylene chloride with WCC temperatures in the range -80 to -30 °C, the requisite temperature depending on the column film thickness (9). Although WCC is a very straightforward operation with GCs capable of subambient programming, an alternative to WCC for trapping the analytes involves the placement of a portion of the front of a narrow bore column in a zone maintained at liquid nitrogen temperatures during the P&T desorption step (11).…”