Polarographic System for Measurement of Dissolved Oxygen

Polarographic System for Measurement of Dissolved Oxygen -...

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Polarographic System for Measurement of Dissolved Oxygen Studies in modern biological science frequently require instrumentation, for measurements such as changes in a quantity with time. A basic recording setup includes a measurement device, a processing or coupling device, and a recorder. In a polarographic system the measurement device (transducer) is a Clark oxygen electrode. The processing/ coupling device is an oxygen monitor. The recording device is a flatbed strip chart recorder, or perhaps a computer-assisted data acquisition system. The solution or suspension to be assayed is placed in a sealed chamber that is exposed to the surface of a Clark oxygen electrode. This dissolved oxygen (D.O.) chamber contains one or more access ports for adding/removing materials. The medium is stirred to ensure homogeneity and to ensure that oxygen can freely diffuse into the electrode. The presence of oxygen causes the electrode to deliver a current to the oxygen monitor, which amplifies the current and converts it to a voltage output that is directly proportional to the concentration of oxygen in the chamber. The recorder moves a paper chart at constant speed, so that when the recorder pen moves in response to voltage changes, oxygen content is recorded as a function of time. For mitochondria studies our medium of choice consists of 70 mM sucrose, 220 mM mannitol, 2 mM HEPES buffer, 5 mM magnesium chloride, 5 mM potassium phosphate, 1 mM EDTA, and 0.1% fatty acid free bovine serum albumin, pH 7.4. In our results we refer to the rate at which total chamber oxygen declines as the oxygen consumption rate. Recommended components For polarographic systems we use custom made glass Gilson type DO chambers that hold a nominal volume of 2 ml. Gilson type chambers are designed with water jackets, however we haven't found it necessary to regulate temperature in our studies. We use the smallest availble "flea sized" stirring bars (maximum 5/16" l x 1/16" dia) to maintain laminar flow in the chambers. For dissolved oxygen detection we use Yellow Springs Instruments (YSI) #5331 Clark electrodes withYSI Model 5300 two channel biological Principle of the Clark oxygen electrode A Clark oxygen electrode is composed of two half cells separated by a salt bridge. A platinum electrode is separated from a solid silver electrode by insulating material. A concentrated potassium chloride solution is held in place over the surfaces of the electrodes by a teflon membrane which is attached by an O-ring that surrounds the electrodes. The oxygen monitor holds a constant voltage difference across the two
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electrodes so that the platinum electrode is negatively charged with respect to the silver electrode. Platinum is a strong catalyst for the covalent dissociation or reassociation of water. In the
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Polarographic System for Measurement of Dissolved Oxygen -...

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