The internal standard diquat-d4 causes errors in diquat analysis by LC–MS/MS
We report a more reliable method for determination of the herbicide diquat (DQ) in human biological samples using stable isotope dilution liquid chromatography–tandem mass spectrometry (LC–MS/MS). DQ-d8, a newly synthesized stable isotope was used as the internal standard (IS) for quantification of DQ instead of DQ-d4 typically used so far. The use of DQ-d8 could completely prevent errors like the misdetection of DQ and inaccurate quantification probably caused by using DQ-d4. Additionally, we developed a method for simultaneous determination of DQ and the similar herbicide paraquat (PQ) in urine, serum and whole blood by stable isotope dilution LC–MS/MS after solid-phase extraction.
The stable isotopes DQ-d8 and PQ-d6 were synthesized and used as ISs. The DQ and PQ in the samples were extracted by solid-phase extraction using an EVOLUTE® WCX. The extracted DQ and PQ were separated and detected by LC–MSMS using a ZIC®-pHILIC column.
The recovery rates ranged from 82.0 to 99.7%. Calibration curves showed good linearity in the 0.01–2 μg/mL. The intraday accuracy and intraday precision [% relative standard deviation (RSD)] ranged from 92.1 to 106% and from 0.4 to 4.7%, respectively. The interday precision (%RSD) ranged between 0.8 and 6.7%.
The stable isotopes DQ-d8 and PQ-d6 allowed for accurate and precise quantification. Especially for analysis of DQ, the use of DQ-d8 could completely prevent errors caused by using DQ-d4. Therefore, the proposed method would be of great use in criminal investigations and emergency medicine.
KeywordsErrors in diquat analysis Internal standard diquat-d4 Paraquat Isotope dilution LC–MS/MS Solid-phase extraction
Compliance with ethical standards
Conflict of interest
There are no financial or other relations that could lead to a conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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