Background: Determination of a reducing substance based on the reaction between
Ce(IV) and a reducing substance and fluorescence detection of Ce(III) generated has been reported
as a selective and sensitive method. However, this method could not be applied to the determination
of alcohol due to the low reaction rate of alcohol and Ce(IV).
Objective: We found that thiosulfate catalytically enhanced the reaction of alcohols (such as, methanol,
ethanol, and propanol) and Ce(IV). Utilizing this effect, we developed a new method for the
determination of alcohols.
Methods: Alcohols were detected using the reaction of Ce(IV) with alcohols in the presence of
thiosulfate and fluorescence detection of the Ce(III) generated by the reaction.
Results: In the presence of thiosulfate, an increase in fluorescence intensity was detected by injecting
alcohol at concentrations of several millimolar, whereas it was not observed even at the concentration
of 10% v/v (2 M for ethanol) in the absence of thiosulfate. The optimum detection conditions
were determined to be 4.0 mM Ce(IV) sulfate and 0.50 mM thiosulfate, and the detection
limit (S/N = 3) of ethanol under these conditions was 1 mM. In the calibration curves, changes in
the slope were observed when the alcohol concentrations were approximately 10–25 mM. Using a
thiosulfate solution containing ethanol as the reaction solution, a calibration curve without any
change in slope was obtained, although the concentration of ethanol at the detection limit increased.
The alcohols in the liquor and fuel were successfully analyzed using the proposed detection method
as a postcolumn reaction.
Conclusion: This new alcohol detection method using a versatile fluorescence detector can be applied
to the postcolumn reaction of HPLC omitting need of time-consuming pretreatment processes.