The reported project demonstrated a novel atmospheric-pressure elemental ionization method where fluorinated compounds separated by gas chromatography (GC) were converted to Na2F+ for nontargeted detection.
The growing use of fluorochemicals has elevated the need for nontargeted detection of unknown fluorinated compounds and transformation products. Elemental mass spectrometry (MS) coupled to chromatography offers a facile approach for such analyses by using fluorine as an elemental tag; however, efficient ionization of fluorine has been an ongoing challenge. In the current project, the compounds were first introduced into a helium dielectric barrier discharge (DBD) for breakdown. The plasma products were subsequently ionized by interaction with a nanoelectrospray ionization (nano-ESI) plume of sodium-containing aqueous electrolytes. The studies pointed to HF as the main plasma product contributing to Na2F+ formation. Moreover, the results revealed that Na2F+ is largely formed by the ion-neutral reaction between HF and Na2A(NaA)n+, gas-phase reagent ions produced by nano-ESI where A represents the anion of the electrolyte. Near-uniform fluorine response factors were obtained for a wide range of compounds, highlighting good efficiency of HF formation by DBD regardless of the chemical structure of the compounds. Detection limits of 3.5–19.4 pg of fluorine on-column were obtained using the reported GC–DBD–nano-ESI-MS. As an example of nontargeted screening, extractions from oil-and-water-repellent fabrics were analyzed via monitoring Na2F+, resulting in detection of a fluorinated compound on a clothing item. Notably, facile switching of the ion source to atmospheric-pressure chemical ionization with the exact same chromatographic method enabled identification of the detected compound at the flagged retention time. (publisher abstract modified)