In the world of the solventless microextraction techniques for volatile organic compounds, the In-Tube Extraction (ITEX) is probably not the most popular one, but definitely the most versatile. Do you know why?
Before answering this question, let me say that over the last 15 years the techniques for the solvent-free extraction of VOCs have improved significantly, leading to better limits of detection (LOD) and reproducibility, while offering a high level of automation for the most demanding throughput laboratories. Besides, many variants based on the same principle have also been developed to improve performance, recovery and applicability. Today the typical limit of detection achievable with the enrichment methodologies is at ppt levels of volatiles.
The three main well-known techniques are headspace (static and dynamic), purge and trap (P&T) and solid-phase microextraction (SPME). Repeatability, detection limit, and carryover/cross-contamination are three of the main challenges. Static headspace has an excellent repeatability with coefficients of variation CV < 2%, with no interference by water, but sometimes the achieved LOD is not enough to comply with some environmental regulation. SPME has a good LOD (below 0.5 μg/L), but may show a worse repeatability (CV > 10 %). The P&T technique offers the lowest LOD, but the system is prone to carry-over effects, making time-consuming cleaning procedures necessary between every sample, especially for analyses of samples containing large amounts of water-soluble materials, suspended solids, high-boiling point compounds, or a high-concentration of volatile compounds.
Dynamic Headspace sampling has a LOD like purge and trap systems1, very good repeatability (similar to static headspace), and allows the elimination of water before the chromatographic run. Carry-over effects are not observed in a wide range of concentration (1–10000 ng/L) as each sample is typically placed and analyzed in individual vials. Well, here is where ITEX is positioned!
How ITEX Works
Within the dynamic microextraction techniques, where the gas sample is actively passed through a sorbent bed for VOC enrichment with successive desorption of the trap at high temperature for GC analysis, ITEX is representing the simplest and most intuitive approach, better responding to the general demand for user-friendliness, reliability, large sample capacity, precision and automated workflow. ITEX uses a gas-tight syringe to withdraw the sample headspace repeatedly through an embedded micro trap packed with sorbent material, in a bidirectional manner, making it a closed-system dynamic headspace technique. Compared to “flow-through” dynamic enrichment, where the sample headspace is flushed through the trapping material in one direction, ITEX does not suffer breakthrough loss of non-retained analytes. This is why ITEX can achieve equivalent enrichment levels as P&T but with a lower sorbent phase volume.
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ITEX is so versatile because of the effortless integration into the Thermo Scientific™ TriPlus™ RSH Autosampler, the variety of sorbents easily adapted to the target analytes and the possibility to adjust the number of strokes according to the required sensitivity.
Additionally, the simplicity of the hardware offers quick access to the trap and it limits the possibility of contamination or leaks in the system.
Dr. Samantha Bowerbank of the Northumbria University, UK recently experienced the versatility of ITEX for the determination of odorants in water with her Thermo Scientific™ ISQ™ 7000 GC-MS equipped with the TriPlus RSH Autosampler. A straightforward method optimization was possible maintaining a low extraction temperature and low extraction flow rate combined with a high desorption temperature and high desorption flow rate. The only trade-off was between the number of syringe strokes for the required sensitivity and the overall cycle time. For this application, sub-ppt LOD have been achieved for the target analytes, maintaining the extraction time plus the GC separation within a cycle time per sample of 12 min.
So, answering the question of why the ITEX is the most versatile solventless microextraction technique for volatiles is simple now.
- Laaks J, Jochmann MA, Schilling B, Schmidt TC (2010) In-Tube Extraction of Volatile Organic Compounds from Aqueous Samples: An Economical Alternative to Purge and Trap Enrichment. Anal Chem 82 (18):7641-7648