Forensic Toxicology

, Volume 36, Issue 2, pp 458–466 | Cite as

The internal standard diquat-d4 causes errors in diquat analysis by LC–MS/MS

  • Yusuke Suzuki
  • Tsuyoshi Kaneko
  • Koichi Saito
Original Article



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.


Errors 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.

Ethical approval

This article does not contain any studies with human participants or animals performed by any of the authors.


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Copyright information

© Japanese Association of Forensic Toxicology and Springer Japan KK, part of Springer Nature 2018

Authors and Affiliations

  1. 1.Forensic Science LaboratoryChiba Prefectural Police HeadquartersChibaJapan
  2. 2.Department of Analytical Chemistry, Faculty of Pharmaceutical SciencesHoshi UniversityTokyoJapan

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