Electrochemical determination of electroinactive guests of beta-cyclodextrin at a self-assembled monolayer interface

A novel determination method of electroinactive molecules by means of electrochemical technique is presented. A new self-assembled monolayer containing cyclodextrin (CD) is prepared with mono(6-o-p-tolylsulfonyl)-beta-cyclodextrin. Although this derivatization process leads to a beta-CD coverage of 10% of a full monolayer, this layer shows an effective host-guest response to ferrocene. The interfacial ferrocene complexation gives a response similar to that expected for a Langmuir adsorption isotherm yielding a stability constant of 4.2x10(4) mol(-1) . L and a maximum ferrocene coverage of 8.6x10(-12) mol cm(2). The redox peak currents of the surface-confined ferrocene decrease upon addition of competing beta-CD guest species to the solution, such as m-toluic acid (mTA) and sodium dodecyl sulfonate (SIDS). This principle has been used for the determination of the electroinactive molecules, mTA and SIDS in the concentration ranges of 0.8-2.7 mumol L and 5-100 nmol L, respectively.