In this study, we developed a fast screening method for the detection of herbicides paraquat (PQ) and diquat (DQ) in human whole blood, serum, and urine by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) after solid-phase dispersive extraction (SPDE).

 Prior to SPDE, whole blood samples and serum samples were deproteinized with acetonitrile. PQ and DQ were extracted from these pretreated samples and urine samples by SPDE with Oasis^® WCX, a mixed-mode, reversed-phase/weak acid cation exchange sorbent. The retained PQ and DQ were eluted with the small amount (8 μL) of matrix solution (saturated solution of α-cyano-hydroxycinnamic acid in 1:1 v/v 0.2 % trifluoroacetic acid in water/acetonitrile).

 The extracted PQ and DQ were instantaneously detected by MALDI-TOF-MS in the positive reflector ion mode. The singly charged radical ions M^+· appearing at m/z 186.11 (PQ) and 184.10 (DQ), and the deprotonated ion [M-H]⁺ appearing at m/z 183.10 (DQ) were mainly observed.

 PQ and DQ were successfully detected from even a small amount (0.1 mL) and low concentration (0.05 μg/mL) of sample assumed mild poisoning. The limit of detection ( S/N >3) for PQ and DQ were 0.002 μg/mL and 0.01 μg/mL, respectively.