A method of quantifying an amount of Brønsted acid sites in an acidic ionic liquid is described. The method involves adding a known amount of at least one silane or borane compound to the acidic ionic liquid being analyzed. The Brønsted acid sites in the acidic ionic liquid react with the silane or borane compound to form a silyl or boryl compound, resulting in an ionic liquid phase and a hydrocarbon phase which contains the silyl or boryl compound. The amount of silyl or boryl compound in the hydrocarbon phase is measured. From the measured amount of silyl or boryl compound formed, the amount of Brønsted acid sites can be determined.