Abstract:

A modified QuEChERS method, based on multi-walled carbon nanotubes (MWCNTs), was established for the detection of 10 pyrethroid pesticides (cyfluthrin, flucythrinate, fenpropathrin, bifenthrin, cyhalothrin, permethrin, cypermethrin, etofenprox, fenvalerate, deltamethrin) in tea, in combination with gas chromatography-tandem mass spectrometry (GC-MS/MS). The purification effects and dosages of four carbon nanomaterials, viz. single-walled carbon nanotubes (SWCNTs), MWCNTs, amino-modified MWCNTs, and graphene, were compared. An orthogonal experimental design was used to determine the optimal experimental conditions for sample pretreatment. The experimental factors governing the process were analyzed using variance. The results showed that the optimized sample pretreatment parameters were as follows. Acetonitrile was used as the extraction solvent with ultrasonic extraction for 35 min, while 60 mg MWCNTs, 200 mg PSA, and 200 mg C18, were used as purifiers. The effects of the extraction solvent and the carbon nanomaterials used on the recoveries of the 10 pyrethroid pesticides were significantly different (p<0.001), and the effect of extraction time on the recoveries was statistically different (p<0.05). The dosage of carbon nanomaterials had no significant effect on the recoveries (p>0.05). Good linearities were observed for the 10 pyrethroid pesticides in the concentration range of 0.01-2 mg/L. The limits of detection (LODs) and limits of quantification (LOQs) were in the ranges of 0.001-0.01 mg/kg and 0.005-0.04 mg/kg, respectively. The average recoveries of the pyrethroid pesticides spiked into blank samples of green tea were 91.4%-109.7%, and the relative standard deviations were 0.12%-9.80% (n=6). Furthermore, the matrix effects (MEs) of scented green tea, green tea, and black tea were evaluated. It was found that the addition of MWCNTs to the purifier can effectively reduce the matrix effect in green tea and black tea matrices. The developed method and the national standard method were used to detect the residues of the 10 pyrethroid pesticides in 120 tea samples available in the market. The results showed that cyfluthrin, deltamethrin, fenvalerate, permethrin, fenpropathrin, cypermethrin, bifenthrin and cyhalothrin were detected, and the contents obtained with the two methods were similar. Although pyrethroids were detected in most tea samples, the contents of all pesticide residues were below the maximum residue limits (MRLs). Therefore, the developed method is suitable for the rapid quantitative analysis of pesticide residues in tea.

Key words: multi-walled carbon nanotubes (MWCNTs), gas chromatography-tandem mass spectrometry (GC-MS/MS), pyrethroid pesticides, tea, matrix effect (ME)