Development of a plasticizer-poly(methyl methacrylate) membrane for sensing petroleum hydrocarbons in water

• Hydrocarbon sensitivity of PMMA-based QCM sensors improves with plasticization.
• Hydrocarbon diffusion in PMMA is dictated by the size of plasticizer molecule.
• The selectivity of PMMA-based QCM sensors can be controlled with plasticizers.

A quartz crystal microbalance (QCM) sensor based on a poly(methyl methacrylate) (PMMA) film has been developed for the detection of aromatic hydrocarbons (i.e., benzene, toluene, ethylbenzene, p-xylene and naphthalene) in aqueous solutions. The PMMA was modified by introducing a plasticizer into the film and the hydrocarbon sensitivity was studied as a function of plasticizer type and concentration. Generally, the PMMA sensitivity for hydrocarbons was shown to be higher in the presence of a plasticizer. However, it was found that some of the plasticizers (i.e., diisooctyl azelate and n-butyl stearate) exhibit much better sensitivity compared to others (i.e., methyl laurate and di-n-butyl phthalate), suggesting that the response of the PMMA film can be tailored by varying the properties of the plasticizer. The relationship between plasticizer type and hydrocarbon sensitivity was investigated and this revealed that the size/molecular weight of the plasticizer molecule plays a significant role. Linear discriminant analysis (LDA) was performed to determine if the QCM sensor array comprising plasticizer–PMMA films are suitable for distinguishing between the various hydrocarbons. LDA modelling revealed that the sensor array can discriminate most of the hydrocarbon analytes investigated in this study.