Brief presentation of the developed pH instrument
The general principle of the instrument developed within BONUS PINBAL is the measurement of the pH value of a continuous sample stream through an injection of a concentrated indicator solution into the stream. The indicator injection leads to a concentration gradient of the dye in the sample water, which is needed for the subsequent detection and recording of the absorbance spectra at high frequency and decreasing dye concentration. These spectra are used for calculation of the pH value of the water sample. The starting point of the development was the scientific instrument and data processing described in Aßmann et al., Ocean Sciences, 7, 597 ff., 2011, and the know how from the development of an automated wet-chemical total alkalinity instrument by partner CONTROS.
The indicator is stored in user-friendly cartridges that allow for a fast and clean plug-and-play exchange of the reservoirs by the operator. The cartridges are placed within the system ensuring a stable temperature of the indicator solution. A second cartridge allows for a regular cleaning by flushing of the relevant parts such as the tubing and the optical path of the cuvette at defined intervals with diluted acid.
The instrument can be run on a continuous water supply as well as in a discrete sample mode. The measurement principle is identical in both cases, with a pre-set number of measurements foreseen in the discrete sample mode. In both cases, a dark and a blank spectrum is recorded before each injection of indicator dye into the sample water.