FemtoGram

A CV of the BDD electrode in water reveals a wide window of useable potentials. This wider potential range now opens electrochemical detection to a wider array of molecules.

ECD Innovations

Boron Doped Diamond Electrode (BDD)

A highly selective and sensitive technique, electrochemical detection (ECD) with HPLC has proven to be of significant value in measuring many biomolecules. It is the method of choice for measuring neurotransmitters in the brain, and has become a standard method in clinical laboratories. Ironically, one of ECD's greatest assests – its selectivity – has also restricted its utility for a number of applications. Traditional materials for working electrodes, all share a common microstructure and demonstrate similar behavior (Au, Ag, Pt, and various forms of carbon – typically glassy carbon and graphite). This has limited the applications for ECD.

Fortunately, advances in materials science and electrode design have expanded the benefits of ECD to a host of new molecules and applications. At the same time that electrochemical detection was being applied to biomedical analysis, material scientists were developing techniques for low-pressure synthesis of diamond films. Diamond is a mechanically strong material, but its SP3 orbital structure makes it notoriously inert and therefore unsuitable for use as a working electrode material. However, inclusion of a metal dopant, such as boron, renders the inherently insulating diamond film conductive, and the combination is an ideal material for the working electrode.

ESA's BDD system brings the benefits of ECD to previously difficult to measure molecules

BDD electrodes have low capacitance resulting in lower inherent noise, a uniform surface, high chemical and structural stability, and resistance to fouling. When used as a working electrode, the BDD can operate with a wider range of working potentials than can glassy carbon. The nature of the BDD material also presents the opportunity to use higher (and lower) potentials than traditional electrodes, even with aqueous mobile phases. Other materials are limited because water is hydrolyzed over a narrower potential range, limiting the set potential that can be used. BDD, with its wider potential window, now allows the detection of molecules that were not amenable to electrochemical detection.

A good example is thiols and disulphide, which have presented problems for traditional carbon electrodes. As discussed in the last FemtoGram, ESA's Coulochem system equipped with a BDD cell enables an optimum working potential of +1400 mV to be used, allowing simultaneous detection of thiols and disulphides without the degradation often seen due to contamination of the electrode surface.

With the wider potential window and the resistance to fouling, the boron doped diamond promises to open many more molecules to electrochemical detection.

An HDV performed on a variety of thiols and disulphides shows that the optimum potential on the BDD electrode is +1400 mV. The use of such potentials with other electrode materials is not practical due to stability of the electrode.

New "chip" electrode design detector.

The BDD electrode is in an easy-to use "chip" format. The ESA BDD electrode is a thin-film amperometric design. The boron doped diamond is deposited on a wafer which is then cut to the proper size and shape for use with the 5040 Analytical cell. This electrode chip is placed into the cell and contact with the electrode and sealing against a gasket is made with the unique pin assembly that makes continuous contact with the working electrode. The cell is then controlled by the Coulochem III.