Analysis of inorganic and small organic ions by CE with amperometric detection

Cathodic preconcentration of f-elements on a mercury film carbon fiber disk microelectrode

Field detection and quantification of f-elements is an important problem in radioanalytical chemistry requiring small, portable devices. Here, characterization of a 10 μm Hg film carbon fiber disk microelectrode to accumulate f-elements is described. Accumulation was performed by cathodic deposition and evaluated by anodic stripping and subsequent ICPMS analyses. La(3+) was used as the model element, and subsequent studies were conducted on a 17 element mixture (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Th). In the model studies, La(3+) undergoes a sorption phenomenon, and as in other studies and confirmed by ICPMS, a monolayer of atoms on the electrode surface is formed. Dissolved O(2) was found to have no effect on the cathodic accumulation of La(3+). Consideration of electrode reaction conditions is made, and reactions are hypothesized. The limit of detection (LOD) was found to be 10(-7) M with mass detection of 10(9) atoms, approximately 5 orders of magnitude less than at conventionally sized electrodes. To solve a dilution problem in follow-on analyses, a suggestion to use microelectrode chip-based sensors was made.

Fundamentals of electrochemical detection techniques for CE and MCE

The electroanalytical techniques of amperometry, conductometry and potentiometry match well with the instrumental simplicity of CE. Indeed, all three detection approaches have been reported for electrophoretic separations. However, the characteristics of the three methods are quite distinct and these are not related to the optical methods more commonly employed. A detailed discussion of the underlying principles of each is given. The issue of possible effects of the separation voltage on the electrochemical detection techniques is considered in depth, and approaches to the elimination of such interferences are also discussed for each case.

Electrode array detector for microchip capillary electrophoresis

Selectivity and resolution for analyses conducted using microfluidic devices can be improved by increasing the total number of individual detection elements in the device. Here, a poly(dimethylsiloxane) capillary electrophoresis microchip was fabricated with an integrated electrode array for selective detection of small molecules. Eight individually addressable gold electrodes were incorporated in series after a palladium current decoupler in the separation channel of an electrophoresis microchip. The electrode array device was characterized using a mixture of biologically relevant analytes and xenobiotics: norepinephrine, 4-aminophenol, acetaminophen, uric acid, and 3,4-dihydroxyphenylacetic acid. Separation efficiencies as high as 9000 +/- 1000 plates (n = 3) for 3,4-dihydroxyphenylacetic acid and limits of detection as low as 2.6 +/- 1.2 microM (n = 3) for norepinephrine were obtained using this device. After characterizing the performance of the device, potential step detection was conducted at the array electrodes and selective detection achieved based upon differences in redox potentials for individual analytes. Utilization of potential step detection was particularly advantageous for resolving co-migrating species; resolution of 3,4-dihydroxy-l-phenylalanine from acetaminophen using potential control was demonstrated. Finally, a human urine sample was analyzed using potential step detection to demonstrate the applicability of this device for complex sample analysis.