Global regulations and consumer concern make pesticide residue analysis an important component of ensuring food safety. With hundreds of pesticides commercially available and approved for use on crops, it is desirable to rapidly and reliably analyse samples for a large number of pesticides in as few methods as possible, typically using liquid chromatography (LC) and gas chromatography (GC), coupled to mass spectrometry. In order to cover a full suite of regulated compounds, several LC and GC methods are often required to incorporate large suites of compounds, single residues and ‘troublesome’ compounds. Phthalimide fungicides, including captan and folpet, are compounds that are considered GC amenable pesticides, but are troublesome to analyse via standard GC analysis. In matrices containing chlorophyll, captan and folpet rapidly degrade in the injector port, making repeatable and robust analysis of these compounds very difficult.
In this project, two LC ionisation techniques were assessed as to their ability to incorporate these problematic GC compounds into an LC method. Electrospray ionisation (ESI) and a novel LC-MS ionisation technique (UniSpray or USI) were investigated to determine whether captan and folpet could be successfully analysed in relevant challenging food matrices, including celery and kale. Initial results show that captan and folpet can be analysed using an LC method using both ionisation techniques. Method optimisation was performed independently on each ionisation technique prior to sample analysis. Linearity was assessed with the matrix samples having R2 values of > 0.99 for both compounds. The methods were also shown to be reproducible (%RSD; n=25) 15%. The data presented demonstrates that the notoriously troublesome GC compounds captan and folpet can be analysed reliably and accurately by LC-MS/MS, avoiding the problems observed using GC analysis.