In this article, we evaluate the performance of a commercially available lifetime-based optode and compare it with data obtained by other methods. We performed a set of 10 different tests, including targeted laboratory evaluations and field studies, covering a wide range of situations from shallow coastal waters and wastewater treatment plants to abyssal depths. Our principal conclusion is that, owing to high accuracy (± 2 µM), long-term stability (more than 20 months), lack of pressure hysteresis, and limited cross-sensitivity, this method is overall more suitable for oxygen monitoring than other methods.

This article reports the performance of an improved, newly developed, compact, low power, lifetime-based optical sensor (optode) for measuring partial pressure of dissolved CO 2 gas (pCO 2 ) in natural waters. The results suggest that after preconditioning, these sensors are stable in water for time periods longer than 7 months. The wide dynamic range of about 0-50000 μatm opens possibilities for numerous applications of which some are presented. In normal marine environments with pCO 2 levels of 200-1000 μatm, the best-obtained precision was about ±2 μatm, and the absolute accuracy was between 2-75 μatm, depending on the deployment and the quality of the collected reference water samples. One limitation is that these sensors will become irreversibly poisoned by H 2 S and should thus not be deployed in sulphidic environments.

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A material support is proposed which grants long-term stability for fluorescence lifetime pH measurements due to a homogeneous chemical microenvironment.