Electrochemical detection of herbicides and plant growth regulators at membrane glassy carbon electrodes

Membrane glassy carbon electrodes modified with cation-exchangers (Eastman AQ-29D, laponite, or polystyrene sulfonate) entrapped between the membrane and the carbon surface were used to study the electrochemical behavior of herbicides and plant growth regulators from the quaternary ammonium family. Cations are shown to incorporate in the entrapped solutions containing negatively charged cation-exchangers, because of favorable electrostatic interactions. In the case of nonelectroactive cations, collection of mepiquat, chlormequat and difenzoquat from the bulk solution is assessed from the competition in ion-exchange equilibrium between one of the above-mentioned cations and the electroactive diquat cation. An attractive property results from the use of spinach ferredoxin as cation-exchanger inside the membrane electrode. Promotion of ferredoxin is shown to be evidenced as a result of the collection of nonelectroactive cations from the bulk solution. Prospects of such modified membrane electrodes in the environmental field are discussed.