Application of microelectrodes for the detection of metallic analytes using thin layer chromatography-square wave anodic stripping voltammetry (TLC-SWASV)

Further studies of Thin Layer Chromatography-Square Wave Anodic Stripping Voltammetry (TLC-SWASV) for the determination of metal ions (Cd{dollar}sp{lcub}2+{rcub}{dollar}, Cu{dollar}sp{lcub}2+{rcub}{dollar}, Pb{dollar}sp{lcub}2+{rcub}){dollar} are accomplished by two modifications of the original TLC-SWASV method developed in our laboratory: (1) Implementation of a glassy carbon mercury film microelectrode (10 {dollar}mu{dollar}m diameter) to replace the original 3 mm diameter glassy carbon mercury film electrode; (2) The development of direct on-plate TLC-SWASV, which incorporates the separation and detection steps in quantitative TLC. In addition, the stability of the mercury film microelectrode is described. Its importance arises from its implementation as a TLC-SWASV detector.; Indirect on-plate TLC-SWASV. Heavy metal ion standards were separated on a carboxymethyl cellulose TLC plate. A canopy containing a thin layer of electrolyte solution was placed over the analyte spot and determined at a mercury film microelectrode using SWASV. Cadmium and lead had detection limits of 1 and 4 ng, linear calibration curves to at least 500 ng, and lead had a relative standard deviation of 22.5% (n = 4).; Off-plate SWASV determination after TLC separation. TLC was used to separate lead and cadmium from humic acid, a ubiquitous voltammetric interferent. Analyte spots were scraped from the TLC plate and quantitated using SWASV. The method sensitivity for lead and cadmium standards containing 100 ppm humic acid was statistically equivalent to standards free of humic acid. This method was also successfully applied to spiked lake water samples.; Stability of {dollar}Znsp{lcub}2+{rcub}{dollar} at a 10 {dollar}mu{dollar}m GCMFE. A spontaneous transition from a reversible to an irreversible SWASV response was noted for Zn{dollar}sp{lcub}2+{rcub}{dollar} at the 10 {dollar}mu{dollar}m GCMFE in quiescent solution. The nature of this transition is consistent with a decrease in the surface area of the mercury film and coalescence of the film into thicker mercury droplets.; Direct on-plate TLC-SWASV. Incorporation of the separation and the detection steps in TLC-SWASV was accomplished by securing a screen-printed microelectrode array to the TLC stationary phase in a homemade TLC development chamber. The analytical performance for Cd{dollar}sp{lcub}2+{rcub}{dollar}, Cu{dollar}sp{lcub}2+{rcub}{dollar}, and Pb{dollar}sp{lcub}2+{rcub}{dollar} are described. Direct on-plate TLC-SWASV was also shown to be effective for standards that contain humic acid.