Experiment 88 Oxygen electrode method

。 Experiment 88 Oxygen ElectrodeWhen studying photodegenerative and respiration in plant physiology, the amount of oxygen release or oxygen absorption is determined, and sometimes certain
reagents
are added to the reaction process to observe its effect on the oxygen change process. Polar spectrometry oxygen electrode (Clark electrode) method is a commonly used oxygen measurement technology in the laboratory, it has a high sensitivity, easy and fast operation, can continuously determine the amount of dissolved oxygen in aqueous solution and its change process, is very suitable for photochromic and respiratory effects and some enzyme reactions in the measurement of oxygen changes, in the laboratory has been gradually popularized and applied.。Principlean electrode consisting of platinum as negative and silver as positive, and when external oxygen diffuses through the film and is reduced on the surface of the platinum pole, the following reaction occurs: O
2
2H

2O 2e→H
2
O
2 2OH
-2O
4e→2O
2- silver pole surface is the following oxidation reaction: 4Ag→4Ag 4Ag4e 4Ag 4CL→

4AgCL: Thecircuit has current through, the current size is directly compared to the concentration of oxygen, the output signal sent to the automatic recorder for automatic recording.。Instrument drugoxygen electrode recorderelectrode controller electromagnetic
agitatorSuper
constant temperature
water bath reaction cupelectromagnetic rod polyethylene film 0.5mol/LKCl saturation sodium sulphate solution operating procedure 1. Installation instrument(1) installation electrode: add a drop of 0.5mol/L KCl to the electrode, cover a layer of polyethylene film with a thickness of 1525 m, set with a "0" ring, carefully cut off the film outside the "0" ring, pay attention to the electrode and film can not have bubbles. The electrode leads to the electrode post of the electrode controller, and the output on the controller connects the signal input of the recorder.(2) connect the two interfaces of the reaction cup to the mouth of the super-heated water bath with rubber tubes. The reaction cup can be secured with a rubber band in the center of the magnetic mixer to keep the stirring speed constant.。 2. The calibration of the instrumentthe oxygen electrodes that dissolve oxygen in the solution are generally marked with water. The amount of dissolved oxygen that is saturated in water is known to be a constant at a certain temperature and atmospheric pressure and can be found in the physical chemistry manual (see Schedule 13). calibration is first filled with distilled water in the reaction cup, add a small magnetic rod, open the thermostat bath and magnetic mixer, and adjust the thermostat bath to the desired temperature, stirring for about 10 minutes, so that the dissolved air in the water to saturate. inserts the installed electrode into the reaction cup, adjusts the polarization voltage knob on the electrode controller, makes the polarization voltage 0.7V, and uses the shift knob to adjust the recording pen to slightly less than the full scale (about 98 squares), so that when the recording pen drifts upward, it can be found in time. Walk the paper for a few minutes, and when the recording pen draws a straight line, it can be marked. Take the syringe to absorb the freshly made saturated sodium sulphate 0.1 ml, inject it into the reaction cup from the electrode plug hole, and absorb the oxygen from the reaction cup water, at which point the recording pen gradually drops underground to near zero (due to residual current, it is actually less than zero). At this point, if the recording pen is away from or above zero, it indicates that the sensitivity knob position on the controller is not suitable, too small or too large, the sensitivity should be increased or decreased, re-test, until the sensitivity selection is appropriate, that is, the recording pen is close to zero, for example, in the 3-grid position. measures the volume of the reaction cup, finds the amount of dissolved oxygen in the water at that temperature from Schedule 13, and then calculates it according to the following formula: A is the amount of oxygen represented by each small grid on the record paper, sl. 。 B is the amount of dissolved oxygen in water, sl/ml (see Schedule 13). 。 V is the volume of the reaction cup, ml. 。 D is the distance from saturated oxygen to anaerobic, recording the distance on the paper, the number of grids. the calibration, the controller in addition to the shift knob and output switch, the other knobs are not moving, the speed knob on the blender can not be moved. The reaction cup and electrode are then washed and dried with absorbent paper before the sample can be measured. 3. Note: (1) oxygen electrodes are sensitive to temperature changes, so the temperature needs to be kept constant during measurement. The temperature of tap water is very stable, the season is suitable for use very convenient. (2) between the electrode surface and the film, and the film surface must not have bubbles, otherwise the needle will be unstable. (3) stirring speed to maintain stability, uneven speed will also make the pointer unstable. The reaction cup should be placed in the middle of the blender and must not deviate. 。