Study On Purification Process Of Avermectins B_1a

As food safety is more well-known, the traditional pesticide with high toxicity and high pollution to environment properties is more concerned by everyone. The unique mechanism of avermectins which is relative low toxic for vertebrate make itself more important in modern agriculture and graziery. The content of B1a is more active than other contents in insecticide resistance therefore purification focused on B1a.National Institution of Metrology need high purity of B1a reference material (purity>99.5%) for Quantitative nuclear magnetic resonance (QNMR) and mass balance approach. This study set up crystallization-Pre HPLC method to achieve the goal. Meanwhile, the study of crystallization method can also provide reference to avermectin industrial crystallization.1. Determined solubility of Avermectins in six pure solvents of methanol, ethanol, isopropanol, n-butyl alcohol, ethyl acetate and cyclohexane with dynamic method over the temperature range from 293K to 323K. Chosen isopropanol and ethyl acetate as solvents, n-proply alcohol and cyclohexane as antisolvents in order to achieve higher theoretical yields. Then determined solubility of Avermectins in mixed solvents of ethyl acetate- n-butyl alcohol, ethyl acetate-cyclohexane, isopropanol- n-butyl alcohol, isopropanol- cyclohexane with dynamic method in the volume ratio from 1:2 to 1:5 and temperature range of 293K-323K. According to solubility data, set up cooling-antisolvent crystallization method and confirmed final system constituent. Then ascertained best volume ratio of solvent and antisolvent.2. The experimental solubility data in pure and mixed solvents were correlated with Apelblat equation, λh equation、RK equation, NRTL equation & Wilson equation respectively. All correlation results were satisfied with the experimental solubility data in pure solvents while λh equation and RK equation didn’t fit solubility data in mixed solvents. The overall ARD with solubility coorelation in pure solvents as follow:1.712 (Apelblat)、2.220 (NRTL)、3.006 (Wilson)、3.114 (λh)、6.635 (RK). The overall ARD with solubility coorelation in mixed solvents as follow: 5.319 (Apelblat),5.189 (Wilson),2.500 (NRTL)3. In order to achieve high purity product and yields coefficient, the effects of crystallization conditions (such as the component of system, crystallization temperature, addition rate of antisolvent, stirring speed) were studied systematically. As a result, the relatively better operation schedule was found. The optimal conditions were demonstrated as follow: (1) ethyl acetate-n-butyl alcohol system:addition rate of antisolvent was 0.8mL/min, stirring speed was 100r/min, the antisolvent-crystallization tempreture was 40℃; (2) ethyl acetate-cyclohexane system:addition rate of antisolvent was 0.4mL/min, stirring speed was 100r/min, the antisolvent-crystallization tempreture was 50℃; (3) isopropanol-n-proply alcohol system:addition rate of antisolvent was 0.4mL/min, stirring speed was 100r/min, the antisolvent-crystallization tempreture was 50℃.4. Studied the change of particle distribution with the effects of crystallization temperature, addition rate of antisolvent, stirring speed.Then the crystallization product were used as raw material purifid by Pre-HPLC with optimal conditions as follow:mobile phase ratio methanol:water=85:15, mobile phase rate is 20ml/min, sample concentration is 25mg/ml, inject volume is 500μL. The final product was desiccate by freeze drier and analyzed with IT-TOF, H-NRM and UPLC. The purity is 99.74% and yields coefficient is 82.2%.