Modification of a SIA-system by addition of a stirrer device (mixing flow cell)

Abstract

The Sequential Injection Analysis (SIA) was developed by Ruzicka and Marshall at the University of Washington and is an automated continuous flow technique. The principle of this method is to measure a continuous flow of reagents and samples with a spectrometer. These measurements form a graph with a peak and the area under this peak is in proportion with the concentration of the solution you want to measure. Phenols or phenolic compounds are chemical compounds that are comprehensive researched, more specifically in food products. In these products, they can be seen as a quality parameter. When phenols are present in food products, there is a relation with the flavor and the color of the food. The group phenols include a large number of compounds. To determine the entire group of phenolic compounds, the colorimetric Folin-Ciocalteu method is the most common method. When using a flow system for the determination of phenols, they minimize the analyst intervention, increase the sampling rate and improve the precision of the measurements but they show also great potential to the development of cleaner analytical methods owing to the lower waste generation. In previous theses, measurements are made with phenols and phenolic compounds. To determine these compounds, a sample and two reagents are needed, but due to bad mixing (no good reaction) between the reagents and the sample in the tubes of the SIA-system, this method is not optimum. The goal of this work is to improve the measurements of one sample and two reagents. A stirrer device (mixing flow cell) is added to the SIA-system to improve the mixing between the sample and the two reagents. The mixing flow cell can also be used to make dilutions from a standard for calibration purposes. First measurements with phenol red are done to introduce the mixing flow cell in the SIA-system and to make the first trials to optimize the stirring cell. For the determination of phenols, calibration lines are made with gallic acid standards. To determine phenols or gallic acid, the Folin-Ciocalteu reagent and sodium carbonate are needed. The reaction between phenolic compounds and the yellow F-C reagent takes place around a pH of 10, by adding sodium carbonate and forms a blue color that is measured at a wavelength of 760 nm. The researched parameters are: accuracy, precision and linearity. When introducing the mixing flow cell into the SIA-system, the method for phenols with a waiting time of 2 minutes gave a good accuracy, linearity and precision from 10 until 100 ppm with an injection volume of 100 μl of the standard. If it is necessary to determine a lower concentration (lower than 10 ppm), the injection volume of the standard must be changed to 900 μl. This is accompanied with a bad precision, but the linear range and the accuracy are still good