Comparison of HILIC columns for residue analysis of dithiocarbamate fungicides

ABSTRACT

Selective determination of dithiocarbamate (DTC) fungicides is mainly performed by hydrophilic interaction liquid chromatography (HILIC). According to Crnogorac and Schwack, DTC analyses by HILIC only lead to meaningful results with a zwitterionic polymer-based hydrophilic interaction liquid chromatography (ZIC-pHILIC) column. Considering the limited availability of this special type of column and the importance of DTC residue analysis, several new HILIC columns were evaluated as alternatives to the ZIC-pHILIC column. Detection was carried out by ultraviolet light and by mass spectrometry (MS) on a single quadrupole mass spectrometer coupled to an electrospray ionization interface operating in negative mode. On nearly all tested columns, separation of dimethyldithiocarbamates, ethylenebis(dithiocarbamates), and propylenebis(dithiocarbamates) was achieved with ammonium acetate eluents (pH 6.8). However, due to ion suppression by the buffer and the limited alkaline pH stability, the tested silica-based columns were not suitable for the sensitive analysis of DTCs. The polymer-based iHILIC-Fusion was the only alternative that offered high MS sensitivity, when a buffer containing 15 mM aqueous ammonium hydroxide and 7.5 mM ammonium hydrogen carbonate (pH 9.8) was used, but the separation of the three DTC subclasses was poor. Thus, considering both selectivity and sensitivity, the originally proposed polymer-based ZIC-pHILIC column still outperformed all the tested newly available alternative HILIC columns.

GRAPHICAL ABSTRACT

KEYWORDS:

• Dithiocarbamate fungicides
• DTCs
• HILIC–MS
• hydrophilic interaction liquid chromatography–mass spectrometry
• ZIC-pHILIC

Acknowledgments

The authors express many thanks to Merck (Darmstadt, Germany) for support with ZIC-pHILIC columns, and to Dichrom (Marl, Germany), Techlab (Braunschweig, Germany) and Macherey-Nagel (Düren, Germany) for providing different test columns.