Controllable Ion-Repulsion Enables Rapid and Trace-Level Detection of Hydrophobic Sulfonylurea Herbicides with ICPMS/MS without the Organic Mode

The inductively coupled plasma tandem mass spectrometry (ICPMS/MS) is emerging as a detector for compounds tagged with a nonmetal, but can be hampered by poor compatibility with organic eluents. Herein, we describe an alternative approach to using high fractions of organic solvents for the detection of hydrophobic compounds while presenting a novel sulfur speciation application involving the determination of a common and widely used class of hydrophobic sulfonylurea herbicides. The approach is based on controllable retention using an ion-repulsion concept, and it is shown that this approach enables minimizing the amount of organic eluent needed for speciation analysis, eliminating the need for the organic ICPMS mode and therefore achieving uncompromised sensitivity. The applied approach enabled fast analysis within 8 min with a mobile phase containing as little as 10% methanol. The limit of detection was 0.3 μg S L^-1 (injection volume 20 μL), which is on par with the lowest achievable LOD for sulfur speciation with ICPMS/MS detection, highlighting the utility of the ion-repulsion approach in overcoming the current limitations of the organic ICPMS mode commonly used with ICPMS detection. Spiking experiments showed the developed method to be directly applicable to a river water matrix with no need for sample preparation or internal standards unlike currently used methods based on ESIMS/MS detection. The ion-repulsion concept is generally applicable to speciation analysis with ICPMS detection for ionizable analytes, provides similar control over retention to organic solvents, and aids in avoiding the limitations of the organic ICPMS mode.