RESONANCE RAMAN OBSERVATION OF SURFACE CARBONYL GROUPS ON CARBON ELECTRODES FOLLOWING DINITROPHENYLHYDRAZINE DERIVATIZATION

Dinitrophenylhydrazine (DNPH) was used to form hydrazone derivatives o f carbonyl groups on glassy carbon (GC) and pyrolytic graphite surface s. The DNPH adducts of benzoquinone and acetone have cross sections of 488 nm, much larger than those of either DNPH or the underivatized ca rbonyl group. The result of this enhancement is that the Raman spectru m of DNPH-modified GC is dominated by adduct features and is not sensi tive to residual adsorbed reagents. In addition, resonance Raman activ e adducts were not formed from DNPH reactions with model compounds con taining lactone, phenol, or carboxylate groups. Assuming that the cros s section of surface carbonyl adducts on GC is comparable to that of t he benzoquinone adduct, the detection limit for carbonyl groups on GC is less than 1% of a monolayer. The coverage of carbonyl groups increa ses significantly following electrochemical oxidation of both GC and h ighly ordered pyrolytic graphite. Analysis of the spectra of the benzo quinone/DNPH adduct permitted assignment of prominent resonance Raman and IR features and revealed that the electrons in the hydrazone linka ge are delocalized extensively.