An apparatus and method for determining a concentration of an additive in a mixture is provided. The apparatus for determining the concentration of an additive in a mixture comprises a distillation system, a filtration system, a detection system and a fluid transportation system. An alternative apparatus is a portable apparatus comprising a distillation system, a filtration system, a detection system and a fluid transportation system removably coupled to a portable container. A method for determining the concentration of the additive in the mixture includes concentrating the additive in the mixture, removing the additive from a fraction of the mixture and measuring a spectral signature of both the non-additive fraction of the mixture and the mixture. A spectral signature value of the non-additive fraction of the mixture to the mixture is determined and then compared to spectral signatures of a plurality of reference mixtures containing known concentrations of the additive.