Product category:
Liquid Analysis: pH, Conductivity, ISE
News Release from: Metrohm UK | Subject: pH electrodes
Edited by the Processingtalk Editorial
Team on 27 July 2004
Care and maintenance of pH glass
electrodes
Information from Metrohm about the care and maintenance of pH electrodes after use
Storage of combined glass electrodes should be in the reference electrolyte, c(KCl) = 3 mol/L AgCl of the reference system dissolves as chloro complex better in solutions containing chloride than in water If a combined electrode is stored in water, AgCl can precipitate in the diaphragm
This article was originally published on Processingtalk on 25 Feb 2008 at 8.00am (UK)
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Separate glass electrodes should be stored in distilled water.
Cleaning the diaphragm.
After measurements in media with low chloride concentration (precipitated AgCl in the diaphragm or dark-coloured diaphragm).
Place the electrode overnight in concentrated NH3, rinse with water and renew the reference electrolyte.
After measurement in sulphide-containing media (Ag2S in the diaphragm or dark-coloured diaphragm).
Place the electrode in freshly prepared, slightly acidic 7% thiorea solution.
Then rinse with water and renew the reference electrolyte.
With organic contaminants.
Place the electrode for approximately 5 minutes in chromosulphuric acid at 80C, then rinse thoroughly and renew the reference electrolyte.
If the above measures do not help, carefully file down the diaphragm with a diamond nail file.
The out flowing electrolyte should be visible as a dark ring.
Care of the glass membrane.
After measurement in non-aqueous media, soak the electrode in water between measurements.
After measurement in protein-containing media, immerse the electrode for several hours in a solution of pepsin in hydrochrloric acid (5% pepsin in c(HCl) = 0.1 mol/L).
Then soak thoroughly.
Regeneration of glass membrane.
Immerse the glass membrane either for 1 minute in a 10% solution of ammonium hydrogenflouride (NH4HF2) or for a few seconds in 40% HF.
After the etching rinse for approximately 10 seconds in an HCl solution (H20:conc HCl = 1:1).
Rinse the electrode with water and allow to stand for 24 hr in the storage solution.
For further information on electrode theory and the Metrohm range of electrodes ask for a copy of the Metrosensor catalogue. Request a free brochure from Metrohm UK ...
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