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• W70155390 abstract "This thesis describes the development and characterisation of optical chemical sensor materials optimised for the determination of pH, pCO2 and pO2 distributions in marine systems via time-resolved luminescence imaging. A new measurement concept for time-resolved mapping of the parameter combinations pH/pO2 and pCO2/pO2 with luminescent dual sensors is introduced. Application examples of planar optodes for imaging of pH and pH/pO2 in natural marine sediments are shown and discussed. Chapter 1 gives a short introduction into the importance of pH, pCO2 and pO2 in marine biogeochemistry, followed by an overview of existing sensors for the three parameters and referencing methods for measurements with luminescent optical chemical sensors. The measuring instruments applied are described in detail in Chapter 2. Modifications made to the imaging set-up are presented and the newly build integrated light source modules are characterised with respect to the intensity and homogeneity of the excitation light field and the resulting irradiance at the optode surface. A set of novel luminescent pH sensor materials with a dynamic range optimised to the predominant pH range in marine systems (pH 7.2 - pH 9.2) is presented in Chapter 3. They are based on two new lipophilic carboxyfluorescein derivatives DHFA and DHFAE applied as pH indicators and immobilised in a polyurethane-type hydrogel matrix. Possible referencing methods (e.g., ratiometric dual wavelength referencing, DLR measurements) are described. The sensors are characterised as to their stability and cross-sensitivity towards ionic strength and temperature. A DHFAE-based DLR sensor foil is successfully applied to visualise pH gradients and dynamical pH changes during a 24 h day/night cycle in a natural marine sediment sample via time-resolved imaging of pH. In Chapter 4, a novel measurement scheme for time-resolved, referenced imaging of pH and pO2 with planar, dual optodes is introduced. The dual sensors examined are composed of a single polyurethane-type hydrogel layer incorporating a fluorescein derivative as pH indicator and the Pt(PFPP) complex as oxygen indicator (= hybrid membrane). In principle, the presented measurement scheme allows the detection of the pH signal as a dual signal dependent on pH and pO2 and the pO2 signal as a pure signal only dependent on pO2. A generally applicable procedure to generate a two-dimensional function describing the pH signal in dependence of pH and pO2 is introduced. Since the hybrid membrane concept leads to an additional influence of pH on the measured pO2 signal an iteration procedure is necessary to calculate the pH and pO2 values of a sample from the measured raw data. The working range of the DHFA/Pt(PFPP) dual sensor (pH 7 - pH 9 and 0 - 400 hPa pO2) meets the requirements for an application in marine systems. It was used for the mapping of pH and pO2 in a marine sandy sediment sample as a proof of principle. In Chapter 5, a luminescent planar dual optode for the intrinsically referenced mapping of pCO2 and pO2 is described. Imaging measurements and their evaluation are performed according to the method introduced in chapter 4. Again the sensor chemistry for both analytes (HPTS/TOA-OH as pCO2-sensing system and Ru(dpp)3 as oxygen indicator) is dissolved in a single layer polymer matrix. Due to a second, ionimpermeable silicone layer the planar dual optode can be applied for the detection of dissolved gases. The optimal working range of the sensor is 0 - 10 hPa pCO2 and 0 - 250 hPa pO2. Therefore, the pCO2-sensing part of the dual sensor is suitable for the detection of most processes in marine systems, which alter the pCO2 such as aerobic or anaerobic respiration. However, its sensitivity is too low for the detection of pCO2 changes in photosynthetically active regions (0 - 0.6 hPa pCO2). In Chapter 6, the influence of the nature of the lipophilic buffer substance on the properties of solid state optical pCO2 sensors is investigated in order to increase the sensor sensitivity. Although sensors incorporating the neutral organic phosphazene base PBO are not superior in respect of their sensitivity towards pCO2, results comparable to TOA-OH-containing sensors are obtained. The fact that PBO bears no fixed positive charge results in a strong cross-sensitivity towards the relative humidity of the analyte gas." @default.
• W70155390 created "2016-06-24" @default.
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• W70155390 date "2006-10-25" @default.
• W70155390 modified "2023-09-24" @default.
• W70155390 title "Luminescent planar single and dual optodes for time-resolved imaging of pH, pCO2 and pO2 in marine systems" @default.
• W70155390 hasPublicationYear "2006" @default.
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