Coulometric Selectivity

Coulometric Sensors in Series

Another advantage of the coulometric electrode is the enhanced selectivity observed when two or more of these electrodes are placed in series.  Because the coulometric electrode measures signal from 100% of an analyte undergoing electrolysis none of the analyte is left to react at subsequent downstream electrodes.

Consequently, if two compounds are unresolved chromatographically then, as long as their half-wave potentials differ by as little as 60mV, they can be resolved voltammetrically (Figure 5). Thin-layer amperometric electrodes cannot be used in this fashion as unreacted analyte would spill over onto subsequent electrodes thereby ruining any voltammetric resolution.

Conclusion

The coulometric electrode offers several major advantages over the thin layer amperometric type including improved sensitivity and selectivity. The coulometric electrode is rugged, maintenance free and is unaffected by changes in flow rate.

Figure 5.  The graph shows that analytes can be resolved both chromatographically and voltammetrically when a series of 12 coulometric sensors are used, each set at successively higher potentials.

References

The following references are recommended for more in depth reading:

Acworth, I.N., and Bowers, M. (1996). An introduction to HPLC-based electrochemical detection: from single electrode to multi-electrode arrays. In: Progress in HPLC,

Acworth, I.N., Naoi, M., Parvez, S., and Parvez, S. (Eds.). VS Press, The Netherlands. In press.

Acworth, I. N. and Gamache, P. H. (1996). The coulometric electrode array: for use in HPLC analysis. Part 1. Theory.

American Lab., 5, 33-37. Svendsen, C. N. (1993). Multi-electrode array detectors in high-performance liquid chromatography: A new dimension in electrochemical analysis. Analyst 118, 123-129.