pH测量中的常见问题.pptVIP

pH玻璃电极的清洗 碱液或水垢 5% HCl 溶液或醋 酸性垢 弱碱 4%NaOH 油,油脂或有机化合物 洗涤剂 与电极材料相容的的有机溶剂 用碳酸氢钠沾上牙刷清洗电极。 检查电缆线 如果端子夹在电缆线外面的绝缘体上，那肯定是接触不良。 端子外要能看到裸露金属才能保证接触良好。 接触不良 接触良好 检查电缆线是否接在正确的端子上，电缆线是否接触良好。 * Some solutions aggressive towards the sensor and cause loss of calibration quicker than others pH 7 + 2.5 needs less calibration than pH 5.2 + 0.2 Quality - who makes it! * Remember from Nernst equation that temperature is involved. Will look at under these headings 1) effect of temperature on the solution itself 2) the Nernstian effect 3) ................... 4)..................... * The recommended useful life of a pH electrode in a benign process is one year. This chart shows the effect of temperature on a typical pH glass electrode. The general rule is that for every 25oC increase in temperature the pH electrode life is cut in half. This is typical for all pH glass electrodes regardless of manufacturer. * Dry - causes pH glass to dry and become non-functional Sore in electrolyte NOT distilled water - why? Draw schematic of diaphragm and effect of osmolarity difference on diaphragm. - increased impedance - unstable diaphragm potential - for electrodes with AgCl saturated electrolyte dilution of electrolyte causes dissociation of argentohalide complexes and precipitation of AgCl in the diaphragm resulting in blockage. * * The general rule for cleaning glass pH electrodes and sensors is to use the mildest cleaning solution that effectively cleans it. It is also a good practice to limit the exposure of the electrode or sensor to the minimum time required for cleaning, so as to minimize any chemical attack on the various sensor parts, and minimize the volume of cleaning solution that is drawn up into the liquid junction. * [File Name or Event] Emerson Confidential 27-Jun-01, Slide * [File Name or Event] Emerson Confidential 27-Jun-01, Slide * [File Name or Event] Emerson Confidential 27-Jun-01, Slide * [File Name or Event] Emerson Confidential 27-Jun-01, Slide * [File