Provided are systems and methods for determining physical properties of solids in solution or suspension. In some embodiments, the present methods employ absorbance for determining the amount of a first material which is adsorbed by a second material when the two are made to contact one another. Through use of the present system and methods it is possible to accurately determine the amount of an air entraining agent which is adsorbed by a particular lot of a fly ash material used in the production of cements and concretes. Use of the technology disclosed herein eliminates errors in formulation of cements and prevents large amounts of waste concrete being generated using prior art methods, which translates to significant savings of resources, both material and financial.