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 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