Use of a Drying Cartridge in On-Line Solid-Phase Extraction-Gas Chromatography-Mass Spectrometry

Abstract

A drying cartridge was used and optimized for the in‐line elimination of water from the desorption eluent in on‐line solid phase extraction–gas chromatography (SPE–GC). The cartridge is essentially a small stainless‐steel precolumn packed with a drying agent which can be regenerated by simultaneous heating and purging with a moisture‐free gas. The drying cartridge was mounted on an additional valve instead of between the SPE–GC transfer valve and the on‐column injector to enable regeneration of the cartridge during the GC run and, thus, to increase sample throughput. Three drying agents were tested, viz. sodium sulfate, silica, and molecular sieves. Although molecular sieves have the highest capacity, silica was preferred because of practical considerations. Large‐volume injections were performed through the in‐line drying cartridge using a mixture of 23 microcontaminants ranging widely in polarity and volatility. Four solvents were tested. With pentane and hexane, the more polar analytes were retained by the drying cartridge. Ethyl acetate and methyl acetate gave much better (and closely similar) recoveries for all analytes. Because water elimination on the silica cartridge proved to be less critical than with ethyl acetate, this solvent was finally selected. The entire SPE–drying cartridge–GC set‐up was combined with mass spectrometric (MS) detection for the determination of a mixture of micropollutants in real‐life water samples. With 10‐ml tap water samples spiked at the 0.5 μg/l level, for the majority of the test compounds the analyte recoveries generally were 60–106%, and (full‐scan) detection limits typically were 0.01–0.03 μg/l. Some very polar analytes such as, e.g. dimethoate, were (partially) sorbed onto the silica packing of the drying cartridge.

Approaches for on-line coupling of extraction and chromatography

“…Since water is not a good solvent for GC, primarily because it hydrolyses the siloxane bonds in GC columns causing deterioration of the column performance, the introduction of water directly to GC should be avoided. After trapping, and before elution of the analytes, the SPE column is often dried with a gas flow, or the extract is dried with a separate drying column packed with copper sulphate or silica to remove water, which is placed after the SPE column [5,6,9,10]. Of these techniques, the use of a nitrogen purge is the more straightforward and easy-to-use.…”

“…Methods based on both SPE-GC and LLE-GC have been developed for a variety of environmental determinations, and SPE-GC has also been used for the analysis of drugs in biological fluids [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,53,54,55,56,57,58,59,60,61,62,…”

Occurrence of residual water within disk-based solid-phase extraction and its effect on GC-MS measurement of organic extracts of environmental samples

“…It is used for matrix separation, rapid clean-up and enrichment of target compounds preceding chromatographic analysis [2][3][4][5]. The technical principle is based on the distribution of analytes between a solid and a liquid or a headspace vapour.…”

“…1) [3,4,6]. Many of the reported methods reduce the remaining water volume on the phase material after the extraction step by actively drying the sorbent [4,5,[7][8][9][10][11][12]. The reasons for this step are manifold [13,14].…”

“…n-hexane, and reduce the recovery of the analytes [9,[15][16][17][18] or can influence the elution strength of solvents by mixing [16]. Furthermore, residual water can disturb the subsequent solvent exchange to another solvent [5]. Reduction of the volume of residual water can also be a prerequisite for a derivatisation step after elution.…”