Thesis (Ph.D.)--Chulalongkorn University, 2011

In this research, automated flow analysis procedures for trace heavy metal determination by a differential pulse anodic stripping voltammetry (DPASV) and square wave anodic stripping voltammetry (SWASV) were developed. A micro-flow sensor consisted of preconcentration membrane and three-electrode electrochemical part with a carbon working electrode was used as a detector. Detection limits (DL) of Cd2+ and Pb2+ were 2.37 and 0.15 µg L–1 by DPASV and 0.02 and 0.01 µg L–1 by SWASV. The results indicated that DPASV and SWASV at the carbon electrode in micro-flow sensor coupled with on-line automated flow system have a good efficiency for the heavy metal ion determination. Furthermore, a low-cost electrochemical flow-through cell based on a carbon paste electrode (CPE) was designed and constructed for the highly sensitive determination of heavy metals by automated flow analysis coupled with SWASV. The sensitivity of the proposed flow-through cell for Cd2+ and Pb2+ ion detection was improved by using the small channel height. Under the optimum conditions, the DL of Cd2+ and Pb2+ ions (0.08 and 0.07 µg L–1, respectively) were 13.8- and 11.4-fold lower than that of a commercial flow cell (1.1 and 0.8 µg L–1, respectively). Moreover, the percentage recoveries of Cd2+ and Pb2+ for the in-house designed flow-through cell were higher than those for the commercially available flow cell in all tested water samples, and within the acceptable range. Finally, an environmentally friendly graphene-modified carbon paste electrode (GCPE) for determination of Cd2+ and Pb2+ levels in an automated flow system was successfully developed. The electrochemical behavior of the developed electrode was studied by cyclic voltammetry and SWASV. The in situ bismuth-modified graphene carbon paste electrode (Bi-GCPE) exhibited excellent electrooxidation of Cd2+ and Pb2+ in the automated flow system with a significantly higher peak current for both metal ions compared with the unmodified CPE. The DLs were 0.07 and 0.04 µg L-1 for Cd2+ and Pb2+, respectively. The Bi-GCPE was also applied for the determination of Cd2+ and Pb2+ in low- (tap water) and high- (sea bass fish and undulated surf clam tissues) matrix complexity samples by SWASV in the automated flow system. The recoveries were acceptable and ranged from 70.4 to 120% for Cd2+ and 65.8 to 113.5% for Pb2+.