Last Month's Most Accessed Feature: Fungicide residue concentration found by GC evaluation

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  • Published: Dec 1, 2017
  • Categories: Gas Chromatography
thumbnail image: Last Month's Most Accessed Feature: Fungicide residue concentration found by GC evaluation

Improved assay methods required for fungicides

Grapes vines are an economically important crop in many countries, but the vines are liable to undergo attack from a range of fungal diseases, especially when grown in large-scale monocultures. A number of fungicides are commonly used to treat such diseases, but these can leave residues in both the grapes and soil. Accurate monitoring of these residue levels is important to prevent harm to humans and the environment.

Boscalid and fludioxonil are two fungicides commonly used on grapes vines. There are many methods of assaying each individually, but up to now there has been no accurate method for assaying both in one run. The Guizhou University researchers have developed a new GC-MS/MS method for assaying both fungicides in grapes and soil. Their aim was to develop a so-called QuEChERS method (an acronym standing for ‘quick, easy, cheap, effective, rugged and safe’), a type of protocol being increasingly used for residue analysis in foods.

GC-MS/MS method suitable for both boscalid and fludioxonil

Samples of grapes and soil were extracted with acetonitrile, which was shown to be superior to methanol, ethyl acetate and dichloromethane, in a centrifuge tube placed in a vortexer. Magnesium sulphate and sodium chloride were added, and the mixture was vortexed again. Solids were removed by centrifugation, and a portion of the liquid was evaporated. The residue was dissolved in acetone. Unwanted substances were removed from the acetone solution using a mixture of C18 (octadecylsilane on silica) and PSA (primary secondary amine, a basic polymer) with vortexing. The combination of these two solids was found to be more effective at removing impurities than either one on its own; GCB (graphitised carbon black) was also examined, but removed too much of the fungicides. A final filtration was carried out prior to GC/MS. This sample preparation is typical of a QuEChERS method; the conditions were carefully optimised using analysis of variance (ANOVA).

GC was carried out using a Thermo Fisher TRACE 1310 GC fitted with a TG-5MS column. The temperature was taken from 110 to 300˚C in a series of ramps. The GC gave clearly separated peaks for the two fungicides. Mass spectrometry employed a Thermo Fisher TSQ 8000 Evo triple quadrupole mass spectrometer, using electron ionisation (EI) in selected reaction monitoring (SRM) mode. Appropriate daughter ion pairs were found for both fungicides.

Standard solutions of the two fungicides were used to validate the method, which was found to give good linearity and reasonable recovery values. The latter varied from 81 to 97%, depending on the fungicide and the matrix (i.e. whether from grapes or soil). The limits of detection (LODs) were 0.006 mg/kg, while the limits of quantification (LOQs) were 0.02 mg/kg (for both fungicides).

The levels of boscalid in grape samples from two regions in China 7 days after spraying were less than the Chinese MRL (maximum residue limit) of 5 mg/kg. The levels of fludioxonil in grapes from both regions 14 days after spraying were less than the US MRL of 1 mg/kg.

New GC-MS/MS method for grape fungicides show promise

The new method allows the relatively quick and accurate determination of two common fungicides in both grapes and soil. It would be advantageous if it could be extended to other agrochemicals. The paper is a good example of the effective optimisation by ANOVA of a QuEChERS method. The authors commented that their results would help towards the setting of a Chinese MRL for fludioxonil, which does not currently exist.

Related Links

Bulletin of Environmental Contamination and Toxicology, Early View Paper. Schenck et al. Evaluation of the quick, easy, cheap, effective, rugged, and safe (QuEChERS) approach to pesticide residue analysis.

Biomedical Chromatography, 2010, 28, 16-27. Zhang et al.. Simultaneous determination of boscalid and fludioxonil in grape and soil under field conditions by gas chromatography/tandem triple quadrupole mass spectrometry.

Wikipedia, Quechers

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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