Evaluation of a single-stage consumable-free modulator for comprehensive two-dimensional gas chromatography: Analysis of polychlorinated biphenyls, organochlorine pesticides and chlorobenzenes

• The performance of a new single-stage thermal modulator was compared to a cryogenic modulator.
• The performance of both modulators was comparable.
• The single-stage, consumable-free modulator simplified the setup of the GC × GC system.

Comprehensive two-dimensional gas chromatography (GC × GC) has been rapidly growing in popularity. The GC × GC separation is performed by interfacing a modulator between two columns of different selectivities. The modulator periodically traps and then re-injects the analytes eluting from the first column into the second column. The most popular GC × GC systems require consumables such as liquid N2 for the trapping function of the modulator. Although these systems are very effective, their costs are a hindrance to more widespread use. A new, single-stage thermal modulator for GC × GC that requires no consumables has been developed and tested. The device traps analytes using a proprietary stainless steel capillary trap compressed between two ceramic cooling pads. Analytes are thermally desorbed from the trap into the second column via resistive heating. To evaluate this system, a routine accredited method for the analysis of polychlorinated biphenyls, organochlorine pesticides and chlorobenzenes was run using the new modulator and its performance was compared to that of an industry standard modulation system. Within-day repeatability (% RSD ranging from 2% to 13%), between-day reproducibility (% RSD from 3% to 15%), as well as between-trap reproducibility were assessed. The results are very encouraging as negligible shifts in retention times (% RSD from 0.3% to 0.6% in the 1st dimension and 0.8% to 2% in the 2nd dimension) were observed for both within-day and day-to-day comparisons of the studied samples (ANOVA, p = 0.9893 for the sediment reference material compared), and the quantitative results were comparable. Routine analysis and quality control applications will benefit from the improved reproducibility as the variances in cold/hot jet flows and temperatures are eliminated. An overview of the device operation and the results from this study are summarized.