Thermo Fisher Scientific Ion Selective Electrodes Silver - Manual (Page 4)

Silver/Silver Sulfide Electrode Instruction Manual
4
times to mix the solution. Store the solution in a brown bottle, tightly capped, in a dark
place.
4.
Eutech Silver Standard, 1,000 ppm as Ag
+
, Code no. EC-SCS-SS2-BT. To prepare this
solution from your own laboratory stock, dry reagent-grade, pulverized silver nitrate in a
laboratory oven for one hour at 150oC. Quantitatively transfer 1.57 grams of the dried
silver nitrate to a 1 liter volumetric flask containing about 500 ml of distilled water. Swirl
the flask to dissolve the solid. Fill the flask to the mark with distilled water, cap, and upend
several times to mix the solution. Store the solution in a brown bottle, tightly capped, in a
dark place.
5.
Chloride Titrant (low level), 2.82X10- 3 M AgNO
3
. Dry reagent-grade, pulverized silver
nitrate as described above in Silver Standards. Quantitatively transfer 0.479 grams of dried
silver nitrate to a 1 liter volumetric flask about half-full of distilled water. Swirl the flask to
dissolve the solid. Fill to the mark with distilled water, cap, and upend several times to mix
the solution. Store in a brown bottle in a dark place.
For Sulfide:
6. Eutech Sulfide Anti-Oxidant Buffer (SAOB) kit, Code No. EC-ISA-SS2-BT. This buffer
must be used fresh and will range in color from clear to yellow-brown. It has become
oxidized when it turns dark brown and should then be discarded. Store fresh SAOB in a
tightly closed bottle. To prepare SAOB from your own stock, fill a 1 liter volumetric flask
with about 500 ml of distilled, de-aerated water, 200 ml of 10M NaOH, 35 grams of
ascorbic acid, and 67 grams of disodium EDTA. Swirl the mixture until the solids dissolve
and fill to the mark with distilled, de-aerated water.
7. Sulfide Standard. To prepare a stock solution of saturated sodium sulfide, add about 100
grams of reagent grade Na
2
S.9H
2
O to 100 ml of distilled, de-aerated water. Shake well and
let stand overnight, storing in a tightly closed bottle in a hood.
Prepare a weekly sulfide standard by adding 500 ml SAOB to a 1 liter volumetric flask,
pipetting 10 ml of the stock solution into the flask, and diluting to the mark with distilled,
de-aerated water.
The exact concentration, C, can be determined by titrating 10 ml of the standard with 0.1M
lead perchlorate. Use silver/sulfide ion electrode (and the reference electrode) to indicate
the endpoint.
The calculation is as follows:
C = 3206 (Vt/Vs)
where
C = concentration as ppm sulfide
Vt = volume of titrant at endpoint
Vs = volume of standard used (10 ml)
Prepare other standards each day by serial dilution of the weekly standard. To do a ten-fold
dilution, accurately measure 10 ml of the standard and add it to a 100 ml volumetric flask.
Add 45 ml of SAOB and dilute to the mark with distilled, de-aerated water.