Liquid chromatography/tandem mass spectrometry analysis of neonicotinoids in environmental water

Neonicotinoids (NNIs) are the fastest expanding group of pesticides in the world over the last two decades; however, they may be a significant contributing factor to bee mortality. The widespread use of NNIs makes it critical to monitor their residuals in the environment. Published methods for NNI analysis are mainly focused on agricultural and food products, and many of them only measured a portion of the commercially available NNIs.

Utilizing a biphenyl stationary-phase column, a sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed to determine eight NNIs, including acetamiprid, clothianidin, dinotefuran, flonicamid, imidacloprid, nitempyram, thiacloprid and thiamethoxam in environmental water. Two multiple reaction monitoring (MRM) transitions were monitored for each compound to ascertain true positive identification. Isotope-labelled NNIs, d3-acetamiprid, d3-clothianidin, d4-imidacloprid and d3-thiamethoxam, were used to compensate for extraction efficiency, matrix effects and instrument variability while monitoring real-time method performance. Target compounds in aqueous samples were analyzed by direct aqueous injection (DAI) or after solid-phase extraction (SPE).

The method detection limits (MDLs) of NNIs in drinking water, surface water and groundwater were in the ranges of 50 to 190 and 2 to 7 ng/L for DAI and SPE procedures, respectively, and target compound recoveries ranged from 78 to 110%. The stability of target compounds in water samples and SPE extracts was also investigated for the first time to ensure accurate results. No obvious degradation was observed for target compounds within four weeks in either water samples or SPE extracts.

The method developed for neonicotinoid pesticide analysis is very sensitive and efficient. It provides good flexibility to meet various environmental monitoring needs and is employed for an extensive study to determine the distribution of NNIs in Ontario's water.