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1、H 电极基础知识,Reference electrode,Measuring electrode,Combined pH electrodes,Active parts of an pH electrode,Measuring electrode: membrane,hydrated layer (0.1 mm),Hydrated layer essential for correct pH-measurement otherwise sluggish response, erroneous results What can lead to disintegration of hydrated
2、 layer? HF solutions pH 4 Long-term in non-aqueous solutions Strongly alkaline solutions at elevated temperatures Stirring in suspension containing abrasive particles Cleaning of membrane with abrasive powder / hard brushes Dry storage of electrodes,Hydrated layer on membrane,Alkali error: Linearity
3、 of glass membrane,Reference electrode: Outflow of electrolyte,Electrolyte solution must be in contact with sample solution Outflow of electrolyte due to hydrostatic pressure If outflow too low Potential more instable and possibly electrolyte contamination (A) Optimal outflow: electrode must not be
4、filled more than once a week (B),Influence of stirring,Active parts of an electrode Membrane, diaphragm Electrode handling & care Storage, rinsing, cleaning Which electrode for which application? Calibration,Contents,Criteria: Membrane must not dry out storage in dist. water Diaphragm salt solution
5、in the inner side store in reference electrolyte exception: c(KCl) = 3 M storage solution pH gel electrode c(KCl) = sat. Other electrodes than pH: Metal (only measuring electrode) needs no special care dry storage Ion selective electrode dry storage,How to store electrodes?,For combined pH glass ele
6、ctrodes with c(KCl) = 3 M Patented storage solution 6.2323.000 - No aging of glass membrane caused by K+ electrode remains ready-for-use - Prevents growth of fungus Effect on sensor:,Storage solution:,Special case: Maintenance free gel-pH electrodes (Ecotrode Gel, Spearhead) c(KCl) = sat. (6.2308.00
7、0) - Routine samples (not for ion deficient solutions!) - Safety Indicator system,How to store electrodes:,Distilled / deionised water Detergent solution Suitable solvent Allow reconditioning after rinsing Do not wipe the glass membrane! Mechanical damage Electrostatic problems,Rinsing of electrodes
8、,Combined electrode must be filled with the correct electrolyte, e.g. c(KCl) = 3 M Reference chamber should be completely filled with clean electrolyte Reference electrolyte filling opening must be - opened during measurement - closed during storage All cable connections should be clean and dry,Care
9、 and maintenance of pH glass electrodes,Rinse electrode thoroughly Remove bridge electrolyte completely Flexible sleeve diaphragms Loosen the ground-joint sleeve (using hot water if necessary) Place empty electrode into the cleaning solution/solvent overnight (diaphragm has to be fully immersed),Cle
10、aning of contaminated diaphragms,Cleaning solutions,Ag precipitates7 % thiourea in 0.1 M HCl Proteins1 % pepsin in 0.1 M HCl Suspensions, fats, oilssuitable solvents Do not etch the glass membrane with HF!,Rinse reference electrolyte chamber thoroughly with reference electrolyte. Do not use water! R
11、efill with reference electrolyte and place it into a beaker with storage solution or reference electrolyte (refilling plug opened).,Never fill a pH electrode with any other than bridge electrolyte. The reference system may be poisoned!,Cleaning,Cleaning and regeneration of pH glass electrodes Electr
12、olyte solution Storage solution Cleaning solution Simple and gentle cleaning (not aggressive),6.2325.000 pHit kit,and of course the leaflet delivered with the electrode,DVD Maintenance and Care of Electrodes,Active parts of an electrode Membrane, diaphragm Electrode handling & care Storage, rinsing,
13、 cleaning Which electrode for which application? Calibration,Contents,Which electrode for which application?,There are many different electrodes on the market How can I know which one is best for my sample? What are the differences?,Properties of different membrane glasses,Membrane glasses recommend
14、ed for pH measurement U glass (green) - low alkali error- high temperatures- high pH values M glass (colorless)- special designs (e.g. flat membrane, Biotrode) A glass (yellow) - for weakly buffered solutions - low conducting solutions - non-aqueous solutions (EtOH-Trode),Properties of different mem
15、brane glasses,Membrane glasses recommended for pH titration E glass (yellow) - aqueous titration T glass (blue) - non-aqueous titration - low electrical resistance U glass (green) - special titrations (high pH SET) - particle loading M glass (colorless)- special designs A glass (yellow) - for weakly
16、 buffered solutions - low conducting solutions,Form of the glass membranes,Half ball (12 mm) Titration,Cylinder Measurement/ Titration,Flat membrane Measurement /Titration,Needle (4 mm) Measurement,Micro cylinder (3 mm) Measurement,Ball (12 mm) Titration,Sleeve diaphragms simply better!,Optimized geometry: Easy to clean and virtually insensitive to contamination Reproducible electrolyte outflow Improved signal stability Less dependence on stirring speed,Ceramic capillary (porotrode),Pt wire (bio
