Fast analysis of semi-volatile organic compounds using PTV-GC–TOF MS

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Courtesy of SepSolve Analytical

The evaluation of semi-volatile organic compounds (SVOCs) in environmental matrices poses many challenges for the analyst, not least the vast number that may be encountered in any given analysis. In addition, analyte reactivity and the potential for multiple analytes to co-elute makes achieving the required method detection limits (LODs or MDLs) quickly and cost-effectively a formidable task – which is especially the case when using quadrupole mass spectrometry in ‘scan’ mode. One approach to improving detection limits is to use selected ion monitoring (SIM). However, even though SIM increases both sensitivity and selectivity, it tends to constrain how fast the analysis can be performed due to SIM window restrictions.

These constraints affect a number of compounds encountered in targeted SVOC suites such as those in US EPA Method 525, including polycyclic aromatic hydrocarbons (PAHs), pesticides and polychlorinated biphenyls (PCBs). As a result, these compounds are generally analysed separately, reducing laboratory efficiency.

Regardless of the detection method used, SVOC analyses are also limited by the GC methodology. For example, robust analysis of N-nitrosodimethylamine (NDMA) and pyridine in accordance with US EPA Method 8270 for SVOC analysis is highly dependent on the injection conditions. For example, splitless injections using dichloromethane as the solvent can cause excessive tailing of these earlyeluting compounds. In practice, a split injection of around 5:1 is commonly used, which reduces solvent loading, allowing analytes to load on to the column more quickly.

In addition, active compounds within the suite of SVOCs listed in Method 8270 can be difficult to analyse, because these compounds can adsorb on any active surfaces within the chromatographic system, which in turn can affect analyte recovery and quantitation.

This study demonstrates the analysis of SVOCs using programmed temperature vaporisation (PTV) to efficiently inject both high mass SVOCs and active species on to the analytical column. Data acquisition is carried out using a BenchTOF time-of-flight mass spectrometer,[1] which offers high sensitivity at the same time as generating high-quality library-searchable spectra.

Experimental

Sample: US EPA Method 8270 mix of SVOCs in dichloromethane (Figures 1 and 2), supplemented with sets of polychlorinated biphenyls and organochlorine pesticides in hexane (Figures 3–7).

GC: Instrument: 7890B (Agilent Technologies). Inlet: Optic-4 PTV (GL Sciences). Note that the optimised run conditions were slightly different for the two sets of analyte standards, leading to the different retention times indicated in the figures and supplementary tables.

TOF MS: Instrument: BenchTOF-HD or BenchTOF-Select (Markes International).

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