Thesis (M.Sc.)--Chulalongkorn University, 2008

Sulfonamides (SAs) were electrochemically investigated at boron-doped diamond (BDD) electrode using cyclic voltammetry. Comparison experiments were carried out using glassy carbon (GC) electrodes. It was found that the BDD electrode provided well-resolved oxidative irreversible cyclic voltammograms and higher current signals when compared to GC electrode. Thus, BDD electrode was used to optimize conditions for the HPLC-EC system. The proposed method was improved by reducing the analysis time using a monolithic column coupled with amperometric detection to determine 7 sulfonamides (sulfaguanidine, sulfadiazine, sulfamethazine, sulfamonomethoxine, sulfamethoxazole, sulfadimethoxine and sulfaquinoxaline). Because of its rapid separation, low back-pressure and high separation efficiency compared to a particle-packed column, a monolithic column (100 mm x 4.6 mm) was used for sulfonamide separation. Chromatographic separation was performed in less than 8 min at flow rate of 1.5 mL min-1. The optimal detection potential using hydrodynamic voltammetry was found to be 1.2 V versus Ag/AgCl. The method was applied to determine sulfonamides in shrimp. The recoveries of sulfonamides in spiked shrimp samples at 1.5, 5 and 10 μg g-1 were in the range of 81.7 % to 97.5 % with a relative standard deviation (R.S.D) between 1.0 % and 4.6 %. This methodology produced results that were highly correlated with HPLC-MS data. Therefore, the proposed method can be used for the rapid, selective and sensitive evaluation of sulfonamides in contaminated food.