NICKEL-TITANIUM ALLOY ELECTRODE AS A SENSITIVE AND STABLE LC-EC DETECTOR FOR CARBOHYDRATES

A highly sensitive and stable amperometric detector for the liquid chromatographic (LC) analysis of carbohydrates has been developed on the basis of the use of a nickel-titanium (Ni-Ti) alloy electrode. Between an applied potential of +0.40 and +0.60 V vs Ag/AgCl, the Ni is electrochemically oxidized to the NI(III) state as the nickel oxyhydroxide. This Ni(III) is believed to be the active form that oxidizes the carbohydrate in an ''ec'' catalytic sequence. This catalysis is similar to that proposed for a pure nickel electrode. Cyclic voltammetric studies with a pure titanium electrode indicated that the titanium did not participate in the carbohydrate oxidation. However, its presence greatly improves the reproducibility and lengthens the useful lifetime of the Ni-Ti electrode in comparison to that of pure Ni. In particular, the Ni-Ti alloy with a 55:45 (w/w) composition, which gives an intermetallic compound with a 1:1 atomic ratio, was effective as an LC detector for carbohydrates in strongly alkaline media. For example, a 100 pmol sample of glucose injected repetitively over a 17 h period showed a relative standard deviation of less than 1.5%. Linear responses covering the concentration range of 10(-3)-10(-6) M were obtained for both reducing and nonreducing sugars. Glucose was detected at concentration levels as low as 5 x 10(-8) M (0.5 pmol). At an applied potential of +0.50 V vs a Ag/AgCl reference, the Ni-Ti electrode exhibited stability for over 40 days of use as an LC detector for the analysis of various carbohydrates without the need for any treatments to reactivate the electrode. The effect of experimental conditions such as the applied potential, mobile phase composition, and flow rate to the sensitivity and stability is discussed for this Ni-Ti electrode.