Herbicides are commonly used for agricultural weed control in production of many types of crops. To help insure public health and safety, reliable analytical methods are necessary to determine residues of these herbicides in agricultural samples. Most unbound (free) acidic herbicides can be extracted from agricultural samples in the same manner as other pesticides using standard QuEChERS methods but the PSA based dSPE cleanup often employed for this analysis is not appropriate for acidic compounds. Although PSA is effective for removal of polar lipids and other anionic interferences it also retains many acidic herbicides resulting in unacceptable low recoveries. For multi-residue screening, a simple pass-through SPE cleanup protocol was developed using a novel reversed-phase sorbent. This protocol is suitable for simultaneous determination of unbound acidic herbicides and base/neutral pesticides from a single aliquot of QuEChERS extract; recoveries of acidic and non-acidic compounds are comparable. However, some acidic herbicides, such as dicamba and 2,4-D, can exist in bound forms (esters or conjugates); determination of the total of bound and unbound residues requires hydrolysis prior to QuEChERS or other manner of extraction. A modified QuEChERS extraction protocol, including a hydrolysis step, was evaluated for determination of dicamba, dicamba metabolites, and 2,4-D.  Cleanup options for the modified QuEChERS method will be discussed.

Strategies for extraction and cleanup prior to LC-MS/MS determination of dicamba and other acidic herbicide residues in agricultural samples; consideration for bound and unbound compounds and metabolites

256th National Meeting (2018)

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