| Decoquinate (6-ethyl-7-ethoxy-4-hydroxy-3-quinoline carboxylate) is a chemical quinolone coccidiostat as a in-feed prophylactic for broiler chickens to prevent and treat coccidiosis. Since it has not been widely used in China, few reports on decoquinate residue study in animal tissues were reported. In this research, the high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) methods were developed for the determination of decoquinate residues in different chicken tissues and applied for the study on pharmacokinetics and residue elimination of decoquinate in chickens, which could provide technical support for the residue monitoring. The main results were as follows:1. A new method based on high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for the determination of decoquinate residue in chicken plasma. The plasma sample was extracted with acetonitrile. The mobile phases consisted of 0.1% formic acid in acetonitrile and 0.1 % formic acid in water (78/22, v/v). The analyte was identified by positive electrospray ionization mode and multiple-reaction monitoring mode (MRM). The results showed as following:The calibration curve showed good linearity within the concentrations of 1 ng/mL～200 ng/mL with the correlation coefficient r~2>0.99. At the spiked levers of 0.5,1 and 50 ng/mL,the recoveries of decoquinate were 85.0%～96.9%. The relative standard deviations (RSD) of intra- and inter-batch were both less than 15%.The limit of detection (LOD) of decoquinate was 0.1 ng/mL and the limit of quantification (LOQ) was 0.25 ng/mL. The method was simple, sensitive and accurate which could be used for the pharmacokinetics study of decoquinate in chickens.2. A new method based on high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for the determination of decoquinate residues in chicken meat, liver and kidney. The sample was extracted with acetonitrile, cleaned with hexane, and purified with HLB solid phase extraction (SPE) cartridge. The analyte was identified by positive electrospray ionization mode and multiple-reaction monitoring mode (MRM). The results showed as following:At the spiked levers of 1.0,10 and 100μg/kg,the recoveries of decoquinate were 75.5%～102.7%. The relative standard deviations (RSD) of intra- and inter-batch were both less than 15%.The limit of detection of decoquinate was 0.25μg/kg and the limit of quantification was 0.5μg/kg.3. A new method based on high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was developed for the determination of decoquinate residue in chicken excreta. The sample was extracted with acetonitrile, and purified with HLB solid phase extraction (SPE) cartridge. The analyte was identified by positive electrospray ionization mode and multiple-reaction monitoring mode (MRM). The results showed as following:At the spiked levers of 5.0,10 and 100μg/kg,the recoveries of decoquinate were 84.4%～100.1%. The relative standard deviations (RSD) of intra- and inter-batch were both less than 15%.The limit of detection of decoquinate was 2.5μg/kg and the limit of quantification was 5.0μg/kg.4. After being orally administrated decoquinate with a single dose of 10 mg/kg b.w., the study on pharmacokinetics of decoquinate in chicken plasma was conducted. The concentration-time data was fit to the two-compartment open model with the first order absorption. The t1/2ka, t1/2α, t1/2βand MRT(0-∞)were 2.614h,3.944h,19.334h and 47.065h respectively, and the Tmax and Cmax were 15h and 43.048 ng/mL respectively, which indicated that the absorption of decoquinate was slow and incomplete, and the elimination of decoquinate in plasma was also slow.5. After being orally administrated decoquinate with a single dose of 10 mg/kg b.w. , the elimination of decoquinate residue in chicken breast, leg, liver and kidney tissues were studied. After a withdrawal time of 1 day, the concentrations of decoquinate was the highest in chicken liver on day one(242μg/kg), the lowest in chicken breast (42μg/kg),but all much lower than the MRL (2000μg/kg) which manifested that the stipulation of withdrawal time of decoquinate in the chicken was right and scientific. The residue in chicken liver were all the highest among four chicken tissues after a withdrawal time of 1 to 5 day. Thereby liver was designated as the target tissue for monitoring decoquinate residue in chickens.6. The study on elimination of decoquinate residue in chicken excreta was conducted. After being orally administrated decoquinate with a single dose of 10 mg/kg b.w., the decoquinate residues at different withdrawal time in chicken excreta were studied. The concentration of decoquinate in chicken excreta was the highest on day one after administration (85.261mg/kg), and eliminate fast to 2.835mg/kg on day two. Within 1 day and 2 days, 65.6% and 75.9% of administrated dose were eliminated from excreta respectively, which showed that decoquinate has few absorption and excreted to the outside mainly via excreta.7. The investigation of decoquinate residue in chicken in Fujian province was studied. Seventy chicken farms were selected randomly and the investigation was conducted, which showed that decoquinate was not use in most farms in Fujian province. Seventy-four chicken meat and liver samples were collected and tested. Decoquinate residues in all samples were below the corresponded LOQ, which indicated that decoquinate is still a new coccidiostat in our province, and has a potential appilcation prospective.In conclusion, for the first time the methods of high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) for the determination of decoquinate residues in chicken plasma, liver, meat, kidney and excreta were established and with these methods the studies on the pharmacokinetics and elimination of decoquinate in chicken were conducted, which submitted the theoretical data for the monitoring of decoquinate residue in chicken products, and give scientific guidance for the revising of the MRL and withdrawal time of decoquinate in chicken.
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