Abstract
Highly sensitive and selective flow-injection (FI) methods are presented for the determination of trace elements at nanogram and/or subnanogram per milliliter levels. These FI methods are based on the catalytic action of the elements on coloration and chemiluminescent (CL) reactions: (1) the oxidative coupling reactions of 3-methyl-2-benzothiazolinon hydrazone with modified Trinder’s reagents, p-anisidine with N,N-dimethylaniline (DMA) and 4-aminoantipyrine with DMA in the presence of hydrogen peroxide; (2) the oxidation of 3,3',5,5'-tetramethylbenzidine, N-(3-sulfopropyl)-3,3',5,5'-tetramethyl-benzidine, N,N'-bis(hydroxyl-3-sulfopropyl)-tolidine and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid by hydrogen peroxide, bromate or periodate; and (3) CL reactions of luminol, lucigenin, pyrogallol and purpurogallin. In order to increase the sensitivity and/or selectivity of the FI methods, suitable ligands that acted as activators and surfactants were used in the catalyzed reaction systems. Elements such as copper(II), chromium(III), cobalt(II), iron(II,III), manganese(II) and vanadium(IV,V) in the range of 10−11∼10−8 M could be determined by the FI methods with easy handling, rapid sampling frequency and good precision. Furthermore, a new approach for the catalytic FI method, FI/standard subtraction, was demonstrated by using the activation and inhibitory effect of a ligand in the metal-catalyzed reaction. The use of CL reactions allowed the determination of the oxidation state of iron and vanadium. These methods have been successfully applied to the determination of trace elements in both standard materials and actual samples.
