XING Yun-tian, DAI Jian-rong, QU Guo-li, LIANG You-sheng, ZHANG Su-yang, FENG Bai-nian
Objective To establish a high-performance liquid chromatography (HPLC) method for measuring the content of niclosamide in Oncomelania hupensis snails, the intermediate host of Schistosoma japonicum, and to investigate the change in the content of niclosamide in snails after treatment with the immersion killing method. Methods The niclosamide standard solution was added to blank O. hupensis snails to prepare the samples with concentrations of 4.00, 0.40, and 0.04 μg/g, and after freeze drying, the samples were crushed with liquid nitrogen in a cryogenic sample crusher. Ultrasonic extraction was performed using carbon dichloride solution containing 4% acetic acid, and then the extracted liquid was blow-dried with nitrogen and redissolved. HPLC was used to measure the content of niclosamide, and precision and recovery were calculated. The snails were immersed in niclosamide solution at concentrations of 8.00, 2.00, 0.50, and 0.12 mg/L and were taken out and washed after 2, 20, 40, 60, 120, 180, 300, 420, and 540 minutes. The snails were then divided into groups 1 and 2; the snails in group 1 were treated with the above sample pretreatment method, and HPLC was used to measure the content of niclosamide; the snails in group 2 were washed and fed for 48 hours, and the knocking method was used to measure the number of dead snails. Results The HPLC method established had a recovery rate of 99.64%-110.36%, with a limit of detection of 0.01 mg/L, a limit of quantification of 0.05 mg/L, and a relative standard deviation of <10%. The concentrations of niclosamide in snails were 1.96, 1.67, 1.08, and 0.98 μg/g, respectively, after exposure to the drug solution at a concentration of 8.00, 2.00, 0.50, and 0.12 mg/L for 2 minutes, with mortality rates of 33.33%, 36.67%, 16.67%, and 0 respectively. After 60 minutes of exposure, the concentration decreased to the lowest level, i.e., 1.32, 0.76, 0.75, and 0.62 μg/g, respectively, followed by a certain degree of increase. Conclusion The established sample pretreatment method and HPLC method can be used for measurement, and the content of niclosamide in snails first decreases and then increases, which requires further studies for explanation.
