Real Time Quantification of Phenol in Aqueous Solutions Using a Quartz Crystal Microbalance
Authors: Barrera Magda Lorena Lorena , Pedraza Julio Andrés , Ríos Fabián Alirio , Garzón Germán Alexander 
Published: February 2020

Phenol (C6H5OH) is an organic compound which is widely used in the industrial production of plastics, paints, rubber, paper, and soaps; However, due to its characteristics of toxicity and persistence in the environment is registered in the list of hazardous substances of the Environmental Protection Agency (EPA) [1,3]. One of the main effluents in which phenol is found are industrial wastewater by which the permissible limits established by the competent environmental authorities are reached, which causes serious problems in the health of people living in places nearby the points of water dump.
There are several techniques and methods for determining phenol concentration in water. Conventional techniques include visible ultraviolet spectrophotometry (UV-VIS), High Performance Liquid Chromatography (HPLC), and Gas Chromatography coupled with Mass Spectrometry (GC-MS). These techniques, although characterized by their precision, require a sample pretreatment, high cost equipment and consumed long analysis times [1,3], which makes it difficult to obtain results in real time that allow the control in the concentration of phenol in water before of being poured.
One of the systems that has gained importance for measuring organic compounds in water and in real time is the Quartz Crystal Microbalance (QCM). This technique comprises a thin quartz crystal sandwiched between two metal electrodes and senses the changes in frequency that suffers the quartz crystal when a certain amount of mass is deposited on its surface [1,3]. In order to improve the sensitivity of the QCM, there have been used coatings on quartz crystal electrode surface, for example for phenols determination polymethylmethacrylate (PMMA) is used. The main objective of this research is to determine in real time and in continuous flow the concentration of phenol in water using the technique QCM with PMMA as coating on quartz crystal electrode surface.
This work is conducted in two stages mainly:1. Determination of a suitable layer of PMMA to use as coating on quartz crystal electrode surface, and 2. Determination of the concentration of phenol using the coating of PMMA prepared in the stage 1.
Results have shown that the PMMA films are more uniform when is used dichloroethane as solvent instead of chloroform, and the stability and sensitivity in the measurements are improved due to its vapor pressure that allows more dispersion of the polymer during spin coating, which is consistent with other authors [2]. The coating of 0.2% w/v of PMMA/dicloroethane allowed the shortest response time with adequate sensitivity. Finally, increase in the concentration of phenol increases the changes in frequency of the quartz crystal in a linear way as shown in Figure 1, which is consistent with other authors [1].
Figure 1. Change of frequency changing concentration of phenol

Keywords

: Quartz crystal microbalance, PMMA, phenol, water, real time.

Mirmosheni, A., Oladegaragoze, A. Application of the quartz crystal microbalance for determination of phenol in solution. 2003. Sensors and Actuators, B: Chemical, Vol.98 (1), p. 28-36.

Mohajerani, E. Morphological and thickness analysis for PMMA spin coated films. 2007. Journal of optoelectronics and advanced materials, Vol. 9 (12), p. 3901-3906.

Reddy, S. Detection of phenol in aqueous solution using an AT-cut quartz thickness shear mode sensor. 2000. Materials Science and Engineering C, Vol. 12 (1), p. 23-28.

Figure 1