Calcium ions are responsible for an important role in the stability of Calcium in milk.  Measurement of Calcium concentration is made by sample addition.

Equipment Required:

  1. Ion analyzer (recommended) or pH meter with millivolt scale.
  2. detectION 3041 Calcium ion selective electrode


  1. Calcium stock solution O.1M Ca2+ (4000 ppm):

dissolve 11.1g of CaCL2 into distilled water in a volumetric flask and dilute to 1000ml.

  1. Prepare calcium standard solutions of 10 ppm, 100 ppm and 1000 ppm by serial dilution of the stock solution (approx 100 ml of each).
  2. Ionic strength adjustment buffer (ISAB) 4.0m KCl:

dissolve 298.2g of potassium chloride into distilled water in a volumetric flask and dilute to 1000 ml.


Take 100 ml of standard and immerse electrode.  Record the electrode potential mV, and then pipette 10 ml of sample solution into sample, stir thoroughly and allow for stabilization.  Record the electrode potential mV2. The change in electrode potential E is given by mV2 – mV1.  Use the sample addition formula (Appendix 1) to calculate the concentration of Unknown.



The slope of the electrode needs to be accurately known.  This can be achieved by taking two standards 100 and 1000 ppm Ca2+   and record the electrode potential difference between the two.  The theoretical value for Ca2+ ISE is +29 mV.  The result from the sample addition formula is a direct measurement.

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