The recent article titled “Acute human self-poisoning with imidacloprid compound: a neonicotinoid insecticide” is very interesting; however, there is a significant typo. In the article the range of plasma imidacloprid concentration is described as 0.02-51.25 ng/L, which is impossible to be quantified by LC/MS/MS with a multiple reaction monitoring (MRM) mode, in general. I think that the unit stated in the article “ng/L” is a typo and the author meant “mg/L”.
We have been researching neonicotinoid metabolites in human urine. We sought to quantify urinary neonicotinoids and a metabolite using Shimadzu MS-8030 LC/MS/MS, which has slightly better sensitivity than Applied Biosystems API-2000 in the article. I observed that the Instrumental Detection Limit (IDL) of imidacloprid was approximately 5 ng/mL with a MRM mode. Since the urinary imidacloprid levels were very low, urine samples were further concentrated by 10-fold. So the final LOQ for urinary imidacloprid was achieved at 0.5 ng/mL, which is equivalent to 500 “ng/L” or 0.0005 “mg/L”.
Meanwhile, the plasma imidacloprid concentrations in your article ranged 0.02-51.25 “ng/L”, which were lower than our LOQ. I examined the method for quantification of plasma imidacloprid in the article. The instrument was API-2000 with a MRM mode; so we assume the IDL is 5-fold less than ours. The sample preparation was protein precipitation with acetonitrile; and the dilution factor was about 8-fold, which is more diluted than our sample by 80-fold. The injection volume was 50 μL, which is 10-times more than ours. Taking those factors into account, I estimate the LOQ for the article to be 0.5*5*80/10 = 20 ng/mL, which is equivalent with 0.02 μg/mL or “mg/L”. The estimation is supported by Proença et al., who reported plasma imidacloprid concentrations by LC/MS with a single ion-recording (SIR) mode; and the LOQ was 0.01 μg/mL or “mg/L” 1).
I think that the unit “ng/L” in the article is a typo of “mg/L”. If it is the case, the concentrations in the article fall in the reasonable range, 0.02-51.25 mg/L, which is the same as or more than the estimated LOQ. Could you check and correct the unit of plasma concentrations?
In addition, the LOQs should be provided in any articles in analytical chemistry, so that readers can easily scrutinize the data. The correction will be helpful for research in bioanalytical chemistry and clinical toxicology of neonicotinoid in body fluids in the future.
References
1. Proença P, Teixeira H, Castanheira F, Pinheiro J, Monsanto PV, Marques EP, Vieira DN. (2005) Two fatal intoxication cases with imidacloprid: LC/MS analysis. Forensic Sci Int. 153(1):75-80.