Chloride in Milk

A rapid and simple method for the detection of abnormal milk  samples using an EDT directION Chloride ISE.

Image showing a combination Ion Selective Electrode.
An image showing a portable ion meter.
Image showing a bottle of 500ml Standard Solution.

Equipment Required:

1. QP459 Portable Ion Meter

2. 3261 Chloride Combination ISE

3. 21301 1000ppm Chloride Standard Solution

4. Dilute Nitric Acid Solution

5. Glassware – Beakers 250ml &1000ml, Volumetric Flask 100ml, 10ml Pipette

6. De-ionised Water



Standard Preparation

Prepare a standard of 100ppm Chloride by serial dilution of the 1000ppm standard. This is achieved by pipetting 10ml of the standard into a 100ml Volumetric flask and diluting to the mark with deionized water. This is now a 100ppm Standard solution. 

Add 1 part of each standard to 2 parts of dilute HNO3



Sample Preparation

Prepare a dilute solution of Nitric Acid (HNO3) by slowly adding 60 ml of Conc. HNO3 to 940 ml of deionized water in an open beaker.

Never add concentrated acid to water !

Add 1 part milk to 2 parts dilute HNO3 and shake for approximately one minute




Pour 100ml of each of the adjusted standards and samples into clean 250ml beakers. Be sure the beakers are clean and make sure not to touch the inside of the beakers with bare hands as contamination from sweat etc. is common. Beakers that have been washed with softened water or tap water will be contaminated. In these cases rinse the beakers with deionised water.

Immerse the electrode in each of the standards in increasing concentration steps in the calibration mode of the Ion Meter, rinsing the electrodes with distilled water and dabbing off the excess water between standards. Read the sample concentration.

Using the QP459 Ion meter will allow the result to be read directly on the display. It also allows for up to a 3 point calibration if required.

If you do not have an ION meter you can read the mV values using a pH/mV meter such as an EDT model QP451. Record the mV response and plot a graph of mV vs log of Concentration.



The major interferent is Casein. This is eliminated by the addition of the dilute HNO3 which 

adjusts the pH of the sample to 2 pH.


Expected Range:

The ‘Upper Limit of Normality’ (ULN) is 40 mmol/l (1420mg/l) Chloride in milk.