Potentiometric Determination of Silver in Film Emulsions

Potentiometric Determination of Silver in Film Emulsions

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
10 mL solution (100 cm2 Ilford black and white film in 100 mL fixing agent Na2S2O3 300 g/L)
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:

AgNO3=EP1*C01*C02/C00*C03/C04/C05;3;g/m2

AgNO3 = amount of AgNO3 in g/m2
C01 = concentration of titrating agent (0.025 mol/L)
C02 = molecular mass of AgNO3 (169.87 g/mol)
C03 = factor for 100 mL sample (100)
C04 = size of sample (0.01 m2)
C05 = conversion mL to L (1000)

Answer

AgNO₃=0.987 x 0.025 x 169.87 / 10 x 100 / 0.01 / 1000 = 4.192 g/m²

EP1 = 0.987 mL
C00 = 10.00 mL
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 Film Ag
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 …3 ml
stop U… OFF mV
stop EP …9
filling rate max…. ml/min
>statistics
status: …OFF
>evaluation
EPC… 5
EP recognition: all
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 Film Ag
>calculations

AgNO3=EP1*C01*C02/C00*C03/C04/C05;3;g/m2

C00= 10.0
C01= 0.025
C02= 169.87
C03= 100
C04= 0.01
C05= 1000
------------
'fr
751 GPD Titrino 15215 751.0010
U(init) -17 mV DET U Film Ag
smpl size.. 10.0 ml id#1 ILFORD
EP1… 0.987 ml…. 52 mV
AgNO3 ….4.192 g/m2
stop V reached
============
'cu
751 GPD Titrino 15215 751.0010
start V 0.000 ml DET U Film Ag
2.0 ml/div dU=50.0 mV/div