Coiled wire filament sample introduction for gas chromatography–mass spectrometry

Abstract

A simple device based on a tiny, coiled wire filament (CWF), similar in operation to solid phase microextraction (SPME), was reported almost a decade ago for sampling, concentrating, and minimizing contamination for Injection of liquid samples in gas chromatography (GC). However, the pliability of the platinum wire from which the CWF was fabricated was a hindrance when using this technique. In this work, we utilized a much stiffer stainless steel wire to form the CWF, and explored a number of ways to use it for sampling and sample introduction in GC and GC–MS. The coil radius and number of turns in the CWF (i.e., length of the coil) determined the sampling volume. The CWF was attached to a retractable plunger (part of a hand-held syringe-type holder) such that it could be retracted inside a 19G needle for insertion into a standard GC injection port. Sampling was easily performed by either dipping the CWF in a liquid sample (i.e., sample dissolved in a solvent), which was drawn up into the wire coil by capillary action, or by applying a specific volume of liquid sample onto the CWF using a micro-syringe. Analytes trapped in/on the CWF could be introduced into the GC injection port before or after solvent evaporation. For semi-volatile compounds, the sample solvent was evaporated before injection, while for volatile compounds, some or all of the sample solvent was retained in the coil during injection. Repeatable volumes from 0.05 to 0.7μL were sampled using CWFs with 5–70 turns, respectively, when sampling by dipping. Advantages of using a CWF compared to a conventional syringe include: (1) the chromatographic system is protected from contamination caused by accumulation of sample residues, (2) high quantitative repeatability is obtained for small volume injections (0.05–0.2μL), (3) large sample injections can be performed for trace analysis by evaporating the solvent before injection, and (4) carryover and discrimination of semi-volatile compounds are minimized. These advantages enable easy and rapid (10min total analysis time) trace (0.1–5ppb) detection of a variety of different types of compounds, including polycyclic aromatic hydrocarbons, biphenyl congeners, organochlorine pesticides, pyrethroid pesticides, phthalate esters, and n-alkanes from C10 to C40 in water and waste water.