A system and method of using a refractive index sensor to determine a characteristic of a sample. The operation of the system and method allow for determining a change in a bulk index of the sample, and an amount of sample adsorption, using a reflected beam from an interface of the sensor. An embodiment of a system and method further provide for identifying changes in incident angles determine from reflective measurement data of the sensor, in combination with different proportionality constants of the refractive index sensor to determine a characteristic of the sample.