GC/MS/MS Determination of Semivolatiles (SVOCs) Using Nitrogen Alone as Carrier, Reagent and CID Gas

New Organic Monitoring Techniques
Oral Presentation

Prepared by D. Stevens, S. Oehrle, F. Dorman
Waters Corporation, 34 Maple Street, Milford, MA, 01757, United States


Contact Information: [email protected]; 508-369-8311

ABSTRACT

Analysis of SVOCs has progressed across the years to include allowances for the use of chemical ionization, MS/MS and hydrogen (H2) as an alternative carrier gas to helium (He). GC/MS has also moved forward with the introduction of atmospheric pressure chemical ionization (GC-APCI). In contrast to vacuum-sourced EI GC/MS, GC-APCI instruments demonstrate specific benefits for multi-residue quantitative analysis especially when paired with tandem quadrupole (TQ) MS. These include generation of intense molecular ions and compatibility with nitrogen (N2) carrier gas, the latter of these being increasingly important due to recurring He supply chain disruptions. EI systems struggle with these capabilities due to extensive fragmentation during ionization and azide formation plus vacuum pump limitations, respectively.

The reactive nature of H2 causes issues with robustness and sensitivity in both the injection port and source of traditional EI GC/MS instruments. Nitrogen is preferred to H2 as a carrier gas due to its inertness. However, working against the adoption of N2 carrier gas is the commonly held belief that it provides decreases in chromatographic resolution, sensitivity and speed of analysis. This work evaluates the GC-APCI MS/MS performance of multi-class SVOCs using both He and N2 carrier gases with the aim of assessing the performance difference between the two.

Samples were analyzed on a XevoTM TQ Absolute (Waters Corp.) tandem quadrupole system fitted with the Atmospheric Pressure Gas Chromatography (APGCTM) source. The APGC source uses 350 ml/min of N2 for multiple functions including acting as the chemical ionization reagent gas. The addition of N2 carrier gas to the source is typically < 1 ml/min and has no effect on ionization or robustness. Analyses were performed using argon CID gas in the TQ and then repeated using N2 for CID gas. Examples of critical pair separations, sensitivity and analysis time will be presented.