No waxy residue for bees: Detecting neonicotinoid insecticides with CE-MS
- Published: Aug 18, 2014
- Author: Jon Evans
- Channels: Electrophoresis
For the first time, analytical chemists from Spain and Germany have used a combination of capillary electrophoresis (CE) and mass spectrometry (MS) to detect neonicotinoid insecticides such as imidacloprid and acetamiprid. Their method is not only quick and sensitive, but it can also detect these insecticides in complex samples such as beeswax.
This is particularly useful, because the effect of neonicotinoids on honey bees has become a contentious topic of late. Derived from nicotine, the neonicotinoids were developed as a safer alternative to older classes of insecticides, as they present less of a health risk to humans and other mammals. Unfortunately, recent research has indicated that they may still pose a danger to bees and may be at least partly responsible for the widespread decline in honey bee populations over the past few years. In response, the European Commission banned the use of three neonicotinoid insecticides – clothianidin, imidacloprid and thiamethoxam – on crops visited by bees for a period of two years from December 2013.
Up to now, combinations of liquid chromatography (LC) and MS have been the most popular method for detecting neonicotinoid insecticides in complex samples such as food. Several research groups have investigated using CE as an alternative, as it can work with smaller samples and use lower amounts of reagents. But it turns out that conventional CE can’t separate the different neonicotinoids, forcing the groups to instead turn to micellar electrokinetic chromatography (MEKC).
This, in turn, meant they had to detect the neonicotinoids with UV detection or laser-induced fluorescence, as MS is unable work with the surfactants required for MEKC. Not only are these other detection techniques not as sensitive as MS, but they often require the samples to be concentrated or modified with fluorescent labels.
It occurred to José Bernal at the University of Valladolid in Spain that there’s an easy answer to this dilemma. Because if you combine conventional CE with MS then it doesn’t really matter that CE can’t separate all the neonicotinoids, because they can still be distinguished from each other by their different mass-to-charge ratios, although no one had tried this before. So together with colleagues at Valladolid and at Aalen University in Germany, this what Bernal set out to do.
As expected, when Bernal and his colleagues tried separating seven different neonicotinoids by CE, they were only able to separate two of them. Four of the neonicotinoids eluted together, while a fifth eluted so closely afterwards that it could not be clearly separated. When these five co-eluting neonicotinoids were analyzed by MS, however, they could all be distinguished from each other by their mass-to-charge ratios. As a result, Bernal and his colleagues were able to detect all seven neonicotinoids at concentrations below 3μg/L in less than 11 minutes, making it more sensitive than MEKC and just as sensitive as LC/MS.
Next, Bernal and his colleagues showed that this method could detect the three neonicotinoid insecticides banned by the EC in beeswax, even though the beeswax did seem to interfere with the electrospray ionization process. They were thus able to try out a practical application for their CE-MS method, by using it to test the effectiveness of a proposed method for removing neonicotinoid insecticides from beeswax by wiping with oxalic acid. This revealed that the treatment did work, reducing all three insecticides to below detectable concentrations. So as well as developing a new method for detecting neonicotinoid insecticides, Bernal and his colleagues have also found an effective way to get rid of them.
Journal of Chromatography A, 2014, 1359, 317–324: "Capillary electrophoresis–mass spectrometry as a new approach to analyze neonicotinoid insecticides"
Article by Jon Evans
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.