MEASUREMENT OF CHLORIDE CONCENTRATION IN MILK BY ION SELECTIVE ELECTRODE (I.S.E.)

A rapid and simple method for the detection of abnormal milk. samples using a Corning Chloride I.S.E.

Equipment Required:

1. Corning pH/ion analyser OR Corning pH meter with milivolt scale.
2. Corning Chloride ion selective electrode.
3. Corning double junction reference electrode.
4. Reference electrode lead.

Reagents:

Dilute HNCL (60ml Concentrated HN(L diluted to 1 litre in distilled water). 1 mol/l Chforide Standard (58.443g NaCI/l in distilled water). 1 mol/l KNO₃ Reference Electrode outer fill solution (101.1 g KNO₃/l in distilled water).

Sample Preparation:

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

Standard Preparation:

Make up standards of 0.1 mol/l, 0.01 mol/l and 0.001 mol/l by dilution of the

1 mol/l standard in distilled water.

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

Method:

Immerse the electrodes in each of the standards, least concentrated first and

most concentrated last, rinsing the electrodes with-distilled water between

standards.

Plot a graph on lin/log graph paper of mV response against standard

concentration.

Immerse the electrodes in the sample and plot sample concentration from the

graph.

Using the M135, this determination may be carried out directly in

concentration units by use of the "Activity" modes. Calculations:

As both standards and samples have been diluted by the same amount the result obtained fromthe graph is the concentration of the original sample.

Expected Range:

The 'Upper Limit of Normality' (ULN) is 40 mmol/l Chloride in milk.

NOTE:     The major interferant with this measurement in casein.

This interference is eliminated by the addition of the dilute HNCL which adjusts the pH of the sample to 2 pH.

Reference: 

Chloride Ion Activity Electrode for the Detection of Abnormal Milk.

Muldoon, P.J., Liska, B.J., Journal of Dairy Science, 54 (1971) 117-119.