Adsorptive stripping voltammetric determination of trace level Ricin in castor seeds using a boron-doped diamond electrode.

Ricin, (Ricinus communis agglutinin, RCA) is one of the most poisonous of naturally occurring substances and has great potential for bioterrorism because no antidote exists. Fast detection at low concentrations is a challenge, and vital to the development of proper countermeasures. In this study, a square wave adsorptive stripping voltammetric (SWAdSV) method for determining RCA using a cathodically polarized boron-doped diamond (BDD) electrode is presented. An irreversible electrochemical RCA oxidation peak was identified on the BDD electrode by different voltammetric techniques using both direct and adsorptive stripping modes. An adsorption-controlled (slope log Ip vs log v of 0.80) pHdependent process was observed. For values of 1.0pH 9.0, the numbers of protons and electrons associated with the oxidation reaction were estimated (ca. 1.0) by differential pulse voltammetry. The RCA oxidation step may correspond to the oxidation of tryptophan amino acid residues, and occurs in a complex mechanism. The excellent analytical performance of the cathodically polarized BDD electrode in combination with the stripping mode ramp was verified with RCA by using a short deposition time in an open circuit potential (120 s). Under optimized analysis conditions, a linear response in the range of (3.3?94.0)3109 mol L1 (r2=0.9944) and a limit of detection of 6.231010 mol L1 were estimated. This LOD is lower than several methods found in the literature. For example, it is 168 times lower than that obtained by using square wave voltammetric with a glassy carbon electrode. Moreover, an even lower LOD might be achieved by using the SWAdSV method with a higher pre-concentration time. In addition, trace levels of RCA were successfully determined in different castor seed cultivars with an overall average recovery from 99.2 1.6% for the three different RCA-A concentration levels. The high accuracy of the analytical data highlights the use of the proposed method for determining RCA in other samples.