Our analytical instrument to measure seawater acidity (pH-value) is an optical pH sensor. Optical chemical sensors, also called optodes or optrodes, are based on a fluorescent indicator dye embedded into a polymer layer connected with a opto-electronic read-out unit. Optodes for oxygen are already well established in marine science and have been commercialized by a number of companies. However, pH Optodes have not been available for measuring pH in seawater up to now.
Our pH Optode consists of a custom designed miniaturized high performance fluororescence measurement instrument with very low power consumption, a build-in data logger and a rechargeable battery. The sensing element is a dye molecule that reversibly changes its fluorescence properties with pH value (comparable with a pH test stripe). The dye molecule is immobilized in a polymer layer on a disposable screw cap. Light from an LED is guided by an optical fiber to this sensor layer and excites the dye molecules.The emitted light is captured by the same fiber and analyzed in the device. All necessary calculations are performed internally by the easy to use software. Our pH Optode is waterproof and can measure autonomously seawater pH without the connection to a computer. pH data are logged and stored in the device and can be downloaded to a computer.