Continuous monitoring of ethanol for bioprocess control by a chemical sensor

This paper describes the first example of continuous process monitoring by a typical chemical sensor. An alcohol-selective optical sensor, based on a solvent polymeric membrane, is applied to continuous monitoring of ethanol produced in a bioreactor. The membrane-incorporated chromophore and ligand, ETH 6022, shows an absorption band at 305 nm wavelength. The sensing principle relies on the base-catalyzed formation of the hemiacetal with ethanol, leading to a hypsochromic shift in the absorption spectrum. Monitoring of ethanol is performed in the vapour phase of the reactor medium without any sample pre-treatment and using the same sensing device for several days. At the same time, for comparative purposes, the ethanol concentration in the liquid phase is determined using the reference method of distillation followed by refractometric density measurement. The selectivity pattern of the sensor with respect to other volatile alcohols in the vapour phase is discussed.