Development of luminescence-based oxygen and pH optodes for toxicity and process monitoring

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Development of luminescence-based oxygen and pH optodes for toxicity and process monitoring


Author: Chan, Chun-man
Title: Development of luminescence-based oxygen and pH optodes for toxicity and process monitoring
Degree: Ph.D.
Year: 2000
Subject: Toxicity testing
Oxygen -- Analysis
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Applied Biology and Chemical Technology
Pages: xxvi, 279 leaves : ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: Oxygen quenching of luminescence of the metal-organic dye ruthenium tris(4,7-diphenyI-1,10-phenanthroline), [Ru(Ph2phen)3(ClO4)2] has been shown to be an accurate method for measuring oxygen concentration. Silicone rubber is commonly used as the matrix for fabrication of oxygen optode due to its high permeability toward oxygen and chemical inertness. However, the low solubility of the ionic ruthenium dye in silicone rubber is a detriment to the performance of the sensor because the ionic dye molecules tend to form aggregates m the hydrophobia environment which leads to inaccessibility of the dye molecules to oxygen quenching. In order to solve this 'solubility' problem, oxygen sensing films were prepared by adsorbing the tris(4,7-diphenyl-l,10-phenanthroline)ruthenium dye onto high surface area hydrophilic fumed silica and dispersing the ruthenium-loaded silica in silicone rubber support. Our results show that these sensing films possess desirable properties including higher luminescence intensity, larger response towards oxygen and more linear Stem-Volmer calibration curves than films prepared by simple mixing of the ruthenium dye with silicone rubber. The applicability of this oxygen optode to toxicity monitoring of organic chemicals to microorganisms has been investigated, An optical scanning respirometer has been developed to measure the dissolved oxygen concentration of wastewater samples by monitoring the luminescence intensity of the immobilized ruthenium dye. The toxicity of various substituted phenols, benzenes and alkanes were evaluated by measuring their effect on the respiration rate of microorganisms which was monitored by the oxygen optode. The IC50 values (concentration of a chemical that exhibits 50% respiration inhibition) of chemicals in activated sludge were found to correlate well with standard methods. The reproducibility and sensitivity of the respirometer were also evaluated and found to be comparable with existing methods. The main advantage of this respirometer is its capability of screening a large number of samples in a short period of time. In addition, the Quantitative Structure Activity Relationship (QSAR) of the toxic chemicals on microorganisms has been worked out based on the collected toxicity data. Five different descriptors including l-octanol/water partition coefficient (log P), aqueous solubility (log S), molecular volume (Vj), molecular connectivity index (MCI) and the combination of log P and ELUMO (energy of lowest unoccupied molecular orbital) have been used for correlating the toxicity of the organic chemicals to activated sludge. The partition coefficient and aqueous solubility were found to be suitable parameters to model substituted alkanes and benzenes. However, molecular volume, molecular connectivity and the combination of log P and ELUMO are the most desirable parameters in the QSAR model as they can cover all three classes of chemicals together. The ability of the developed models for predicting mixture toxicity has also been investigated. The accuracy of the developed MCI and log S QSAR equations are superior over other models in mixture toxicity studies. A luminescent ruthenium complex [Ru(bpy)2(dhphen)]2+ (bpy = 2,2'-brpyridrnev dhpnen = 4,7-dihydoxy-1,10-phenanathroline) was immobilized into a Nation film as art optical pH sensor. This pH optode displays pH-dependent luminescent intensities and exhibits advantages over existing optical pH sensors including wide dynamic pH range, ease of fabrication, high sensitivity, good photostabifity and minimal interference from metal cations. The application of this optical pH sensor to pH monitoring of fermentation by Klebsiella pneumoniae has been investigated. The experimental results showed that interference from the culture medium can be eliminated by addition of a black microporous filter membrane on top of the sensing film. The response of this pH optode was found to show good correlation with the conventional pH electrode.

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