LIMITS OF QUANTIFICATION OF SOME NEONICOTINOID INSECTICIDES MEASURED BY THIN-LAYER CHROMATOGRAPHY

Abstract

A simple method to quantify the neonicotinoid insecticides nitenpyram, thiamethoxam, acetamiprid, imidacloprid, thiacloprid, and clothianidin directly on an HPTLC-plate is presented. As stationary phase silica gel 60 RP-18WF254 s plates were used and a mixture of methyl-t-butyl ether, 2-butanone, NH₃ (25%) (5 + 2+0.1, v/v) was used as solvent. All neonicotinoid insecticides show light absorptions below 300 nm. The calculated limits of quantification (LOQ) by UV-detection were in the range from 12 ng to 26 ng on plate depending on the different insecticides.

Nitenpyram can be stained using fast blue salt B, forming red zones. The observed LOQ is 25 ng on plate. Acetamiprid can be specifically stained using phenylglyoxylic acid forming a yellow/green fluorescent compound. The LOQ is 52 ng per spot.

The compounds thiamethoxam, acetamiprid, thiacloprid, and clothianidin can be transformed into blue fluorescing zones, using a relatively new staining solution. This consists of tetraphenylborate and HCl. This is the first publication mentioning that neonicotinoids undergo this reaction. The calculated limits of quantification are in the range from 10 ng to 27 ng on plate.

A simple pre-treatment procedure using an acetonitrile extraction and a Chromabond SiOH clean up procedure leads to overall LOQs for bee samples of 48–108 µg/Kg. The method can be used to measure neonicotinoid contaminations of bees.

Keywords:

• acetamiprid
• clothianidin
• HPTLC
• imidacloprid
• insecticides
• limit of quantification
• linear calibration range
• neonicotinoid
• nitenpyram
• thiacloprid
• thiamethoxam
• TLC

ACKNOWLEDGMENT

The authors express their thanks to Merck-Company (Darmstadt, Germany) and DESAGA GmbH (Wiesloch, Germany) for their support.