Determination of spirodiclofen in dragon fruit and risk assessment for dietary residue intake

Abstract:【Objective】The present study developed a method to determine of spirodiclofen based on liq-uid chromatography triple quadrupole mass spectrometry (LC-MS/MS), which is widely used in analyti-cal labs. We investigated the behavior of terminal residues of spirodiclofen in dragon fruit and flesh un-der field conditions, risk assessment for dietary intake based on supervised residue trial data, the effects of application frequency and rate and of the interval to harvest on terminal residues.【Methods】The su-pervised field trials were carried out in six provinces in the year of 2018. Two treatments were included in this study to determine spirodiclofen residues at high and low application rates. Each treatment had 3 replicated plots, and each plot consisted of 2 dragon trees. The low application rate was 80 mg·kg^-1 and the high application rate 120 mg·kg^-1. Both the low and high application rates were used in two or three applications (14 days intervals each). The dragon fruit and flesh were sampled at 7, 14 and 21 days after the last spraying. Immediately after collecting, the samples were put into polyethylene bags and trans- ported to the laboratory. The fruit stalk of the dragon samples collected in the field was cut off. The dragon fruit were evenly cut into 4-8 portions along the longitudinal direction. The nonadjacent fruit pet- als were divided into two groups. The first group was used to prepare the whole fruit samples, and the second group was used to prepare the flesh samples. All the samples were crushed with dry ice and were packed in polyethylene bags, labelled, and stored at -20 ℃ until analyzed. 10 g subsample of ho mogeneous dragon fruit and flesh was put into a 100 mL centrifuge tube, and 5 mL distilled water, 20 mL acetonitrile (HPLC grade), and 2.5 g sodium chloride were added in turn. The sample was vortexed  for 10 min at high speed on a vortexer. The mixture was centrifuged at 4 000 r·min^-1 for 5 min, and 2 mL of the supernatant was transferred to a 2 mL centrifuge tube containing 0.05 g PSA and 0.02 g GCB, vortexed for 1 min at 4 000 r·min-1 for 5 min, and filtered into a glass autosampler vial through 0.22 μm pinhole filtration membrane for LC-MS/MS analysis. The column used for spirodiclofen deter-mination was a Shim-pack GISS (2.1 mm × 50 mm，1.9 µm), maintained at 40 ℃. The mobile phases A and B were acetonitrile and water with 0.1 percent formic acid (80∶20, V/V), respectively. Electrospray ionization MS in the positive mode was performed. The flow rate was 0.3 mL·min^-1. The cone and frag-ment voltages were 16 eV and 11 eV, respectively. The temperature and flow rate for drying gas were 400 ℃ and 10 L · min^-1, respectively. The ions monitored in MRM were m/z 411.1/71.2 and 411.1/ 313.05 (qualitative ion pair), and 411.1/71.2 (quantification ion pair). The retention time of spirodi-clofen was 1.3 min at the above conditions. The IEDI was defined according to the formula IEDI=[ST-MRi (or STMR-Pi)×F]/bw. The ADI% was calculated according to the formula ADI%=(IEDI×100%)/ADI.【Results】A standard calibration curve of spirodiclofen was constructed by plotting the analyzed concentrations against the peak areas. Good linearity (y =28 570 214.614 9x+9 992.204 6) was achieved in the range of 0.002 to 0.5 mg·L-1, with a correlation coefficient of r2=0.990 0. The recovery study was conducted for dragon fruit at three different fortification levels of 0.01, 0.1, and 5 mg·kg^-1. The average recovery from the fortified samples in five replicate experiments ranged from 87% to 105%, with a rela- tive standard deviation (RSD) from 4.6% to 13%. The limits of quantification (LOQ) were 0.01 mg·kg^-1 for dragon fruit. The recovery study was conducted for flesh at three different fortification levels, 0.01, 0.1, and 1 mg · kg^-1. The average recovery from the fortified samples in five replicate experiments ranged from 81% to 90%, with a relative standard deviation (RSD) from 6.6% to 81%. The limits of quantification (LOQ) were 0.01 mg·kg^-1 for flesh. When the intervals to harvest were 7, 14, 21 day, the residue levels in dragon fruit were less than 0.71, 0.23 and 0.68 mg·kg^-1, respectively and those in the flesh were less than 0.14, 0.059 and 0.041 mg·kg^-1, respectively. Under identical application dosage and application frequency, the residue decreased with the increase of interval to harvest, indicating that there was a negative correlation between the residue and interval to harvest. However, under the same application dosage, application frequency and interval to harvest, the residue in the whole fruit was higher than in the flesh. The international estimated daily intake (IEDI) of spirodiclofen was 0.003 1mg, and the ADI% was calculated according to formula and found to be 0.5%, the potential health risk induced by spirodiclofen was not significant based on supervised residue trial data.【Conclusion】A spe- cific, sensitive and simple residue analytical method using LC-MS/MS for the detection and monitoring of spirodiclofen in dragon fruit and flesh was established. When the application of spirodiclofen followed the recommended methods, the potential health risk induced was not significant.