DETERMINATION OF SILVER CONCENTRATION IN FIXER SOLUTIONS

This is a method for the determination of silver ion concentration in hypochloride based fixer solutions in the range of 10^-1 to 10^-6 M Ag⁺ .

Equipment Required

1. pH/ion analyzer or pH meter with millivolt scale
2. Silver ion selective electrode

Reagents

1. Ionic strength adjustment buffer (ISAB) - This should be 2M KNO₃
2. Silver nitrate stock solution (l.OM)

Standard Preparation

Prepare standards of 10^-1, 10^-2, 10^-3 and 10^-4M Ag⁺ by serial dilution of .the 1.0M stock solution. Mix equal volumes of each standard and the ISAB.

Sample Preparation

Dilute the sample 1:1 with distilled water. Mix equal volumes of sample and ISAB.

Method

Immerse the electrodes in each of the standards in increasing concentration steps, rinsing the electrodes with distilled water between standards and record the mV response of the electrodes. Plot a graph of mV response against standard concentration on semi-log graph paper.

Immerse the electrodes in the sample solution, record the mV response and plot sample concentration from the graph.

This determination may be carried out directly in concentration units by use of the "activity" modes on Corning pH/ion analyzers.

Calculations

The result obtained from the graph should be multiplied by the dilution factor to obtain Ag concentration of the sample.

Interferences

 Mercury ions should not be present in concentrations greater than 2 x 10^-7 moles/liter.

4. Immerse the electrodes in the sample solution (previously diluted with ISAB) and record the mV reading.
5. Read the concentration of the sample from the standard curve.

Calculation:

To obtain the actual concentration of KCl in the syrup multiply the reading from the graph by 10.  (units = moles/liter).