High throughput screening of lead utilising disposable screen printed shallow recessed microelectrode arrays.

The cathodic stripping voltammetry of lead at disposable screen printed shallow recessed microelectrode arrays has been developed for the first time. The array comprises 6 microdiscs which have radii of 116 (+/-6) microns which are recessed by 4 microns and are separated by 2500 microns from their nearest neighbour in a hexagonal arrangement. The electroanalytical determination of lead was explored in 0.1 M nitric acid and found that using a 120 s deposition time, a detection limit of 3 microM is feasible which is not possible utilising a screen printed graphite macro-electrode. The sensitivity of this analytical protocol can be tailored by varying the deposition time and it is found that increasing this to 320 s facilitates a limit of detection of 39 nM. This methodology is shown to be feasible for the portable and economical screening of lead in river water samples at the levels indicated by the EC Dangerous Substances Directive (76/464/EEC).

Why 'the bigger the better' is not always the case when utilising microelectrode arrays: high density vs. low density arrays for the electroanalytical sensing of chromium(VI).

We demonstrate, with the example of the electroanalytical sensing of chromium(vi) using ultra-microelectrode arrays, that a larger number of microelectrodes comprising an array do not necessarily provide improved electroanalytical performance. Using a low density array, which consists of 256 microdiscs where each microdisc comprising the array has a radius of 10 microns in a cubic arrangement separated from their nearest neighbour by 100 microns, the electroanalytical sensing of chromium(vi) is shown to be possible over the range 13-428 microM with a limit of detection of 3.4 microM readily achievable. Using a high density microelectrode, consisting of 2597 microdiscs where each microdisc has a radius of 2.5 microns in a hexagonal pattern which are separated from their nearest neighbour by 55 microns, the electroanalytical performance, in terms of linear range and sensitivity, is considerably lower going against the misconception that a high density array should produce a superior analytical response. The reason for this disparity is discussed and it is shown that the arrangement of the microelectrodes on the array is critical due to the interaction of diffusion zones between neighbouring electrodes allowing analysts to make informed decisions on the conscientious choice of microelectrode arrays.