Abstract: This invention provides apparatus and a method for measuring the concentration of alumina in a molten electrolyte in a smelter. A test anode (101) (a mimic of the actual cell anode) supplied from a computer-controlled voltage source (303) with several to about (100) rapid cyclic voltammetry sweeps the voltage at which the anode effect occurs, as sensed by current measurement (305). In order to derive a measurement the voltage is compared within the computer (301) to previous measurements made from a calibration set of alumina samples in known concentrations. Brief rapid cycles and an improved electrode configuration help to provide results from the invention which are reproducible and accurate, and in addition the test electrode has a long life.