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

Dinitrophenylhydrazine (DNPH) was used to form hydrazone derivatives of carbonyl groups on glassy carbon (GC) and pyrolytic graphite surfaces. The DNPH adducts of benzoquinone and acetone have cross sections of 488 nm, much larger than those of either DNPH or the underivatized carbonyl group. The result of this enhancement is that the Raman spectrum of DNPH-modified GC is dominated by adduct features and is not sensitive to residual adsorbed reagents. In addition, resonance Raman active adducts were not formed from DNPH reactions with model compounds containing lactone, phenol, or carboxylate groups. Assuming that the cross section of surface carbonyl adducts on GC is comparable to that of the benzoquinone adduct, the detection limit for carbonyl groups on GC is less than 1% of a monolayer. The coverage of carbonyl groups increases significantly following electrochemical oxidation of both GC and highly ordered pyrolytic graphite. Analysis of the spectra of the benzoquinone/DNPH adduct permitted assignment of prominent resonance Raman and IR features and revealed that the electrons in the hydrazone linkage are delocalized extensively.