Abstract: An apparatus for measuring a sorbate dispersed or dissolved in a fluid stream and comprising an oscillator for generating a first alternating-current signal, an acoustic transmission line for disposition in the fluid stream and including an elongated body having a surface capable of sorbing an amount of the sorbate to be measured representative of the concentration thereof in the fluid stream, the body being capable of propagating acoustic energy along its length from one end portion to another end portion, the propagated acoustic energy being damped in amplitude and shifted in phase such that the change in amplitude or phase is proportional to the amount of sorbate sorbed by the surface, a first transducer for converting the alternating current signal to acoustic energy and for applying the acoustic energy to the one end portion, a second transducer for converting the acoustic energy propagated to the other end portion to a corresponding electrical signal, and a comparator for comparing the electrical signal