Potentiometric Determination of Silver in Fixing Baths

Potentiometric Determination of Silver in Fixing Baths

Equipment
Potentiometer = 751 GPD Titrino / Titroprocessor
Electrodes = 6.0430.100 Ag Titrode with Ag2S coating; input 1

Reagents
c(Thioacetamide) = 0.025 mol/L in buffer pH = 5

Sample
5 mL of sample
20 mL c(NaOH) = 2 mol/L
20 mL c(EDTA) = 0.1 mol/L
10 mL w(gelatine) = 0.12 (12%)

Remarks
Determination reaction:

S O

CH3C + OH+ + 2 Ag+ ........CH3C + Ag2S (s) + H+

NH2 NH2

Calculations:

Silver=EP1*C01*C02/C00;3;g/l

Silver = Ag content in g/L
C01 = Ag equivalent (5.394 mg/mL titrating agent)
C02 = titer of titrating agent (1.000)
EDTA keeps silver in solution and gelatine prevents the precipitation from massing together.

Ag2S coating of electrode:
Keep Ag Titrode in alkaline solution of thioacetamide during 15 min.

Buffer pH = 5:
Mix potassium biphthalate solution, c = 0.1 mol/L with Na3PO4 solution, c = 0.05 mol/L. Ratio 50:24. Dissolve 0.5 g thymol per liter buffer solution.

Titrating agent:
Dissolve 1.9 g Thioacetamide in 1 L buffer pH = 5 solution.

Gelatine solution:
Dissolve 12 g gelatine in hot water, add 0.5 g thymol, allow to cool and add up to 1 L.

Literature
Metrohm Application Bulletin No. 72: Potentiometric determination of mercury or silver in the presence of halide ions.

Method documentation

'pa
751 GPD Titrino 15215 751.0010
DET U FixBaths
parameters
>titration parameters
meas.pt.density… 4
min.incr. ….10.0 ml
dos.rate max….. ml/min
signal drift ….20 mV/min
equilibr.time ….38 s
start V: ….OFF
pause ….0 s
dos.element:… internal D0
meas.input: ….1
temperature ….25.0 °C
>stop conditions
stop V: ….abs.
stop V ….12 ml
stop U…. OFF mV
stop EP…. 9
filling rate max…. ml/min
>statistics
status:…. OFF
>evaluation
EPC…. 5
EP recognition: greatest
fix EP1 at U…. OFF mV
pK/HNP: ….OFF
>preselections
req.ident:…. OFF
req.smpl size:…. OFF
activate pulse:…. OFF
------------
'fm
751 GPD Titrino 15215 751.0010
DET U FixBaths
>calculations

Silver=EP1*C01*C02/C00;3;g/l

C00= 5.0
C01= 5.394
C02= 1.0000
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) -168 mV DET U FixBaths
smpl size…. 5.0 ml
EP1…. 10.220 ml…. 99 mV
Silver …..11.025 g/l
stop ….V reached
============
'cu

751 GPD Titrino 15215 751.0010
start V 5.000 ml DET U FixBaths
2.0 ml/div dU=100.0 mV/div