Novel Optical Techniques for Measuring Hydrogen Peroxide in Industrial Sample Media

Novel Optical Techniques for Measuring Hydrogen Peroxide in Industrial Sample Media Hydrogen peroxide is commonly used in bleaching processes (e.g. in textile and paper treatment), chemical oxidation processes in general and for sterilisation purposes. The determination of the concentration of hydrogen peroxide in these solutions is of great technological, ecological and economical importance. The methods and instruments for the determination of this substance, which are commercially available, are time consuming, costly, cannot be used for on-line monitoring or are not applicable for hydrogen peroxide concentrations used in the mentioned applications. In the work presented here two completely different approaches were investigated for the determination of hydrogen peroxide concentration in the range of 0,1 – 10 % by weight in industrial sample solutions. For the first approach a novel hydrogen peroxide sensor based on an optochemical oxygen sensor was developed. An oxygen sensitive membrane was covered with an additional layer containing inorganic catalysts which decompose hydrogen peroxide to water and oxygen. The oxygen was detected in the underlying oxygen sensitive membrane via luminescence quenching. Several catalysts were tested for this application with manganese dioxide being the preferred material. In addition it was shown that by coating the sensor with a proper polymer layer the hydrogen peroxide sensitivity could be improved for up to 5 times compared to an uncoated sensor. This approach was found to be suitable to detect lower hydrogen peroxide concentration (0,1 - 2%) in sample solutions with small variations in the background oxygen concentration. The second approach is based on the determination of the hydrogen peroxide concentration by means of direct spectroscopic methods. The absorption of hydrogen peroxide in aqueous solutions in the mid-infrared and near-infrared regions was investigated. In the mid-infrared region the technique of attenuated total reflection (ATR) of infrared light was applied for measuring of hydrogen peroxide, whereas in the near infrared region the transmission of the sample solution was measured in quartz cuvettes. The infrared spectrum of hydrogen peroxide displays the OH-stretching and deformation vibrations. Additionally the O-O stretching vibration can be found. In the near infrared region overtone and combination vibrations of the basic vibrations in the mid-infrared can be observed. These specific vibrations were used for quantitative determination of hydrogen peroxide in aqueous solutions. The spectrum of water did not interfere with these measurements. Additionally a chemometric model to determine hydrogen peroxide concentrations in the near infrared region independent from temperature, pH and ionic strength was developed. The spectroscopic approach displays a very robust method to determine higher hydrogen peroxide concentrations (0,5 – 10 %) in nearly all industrial oxidising solutions. The performance of this method was tested with various spiked industrial sample solutions.