The presence of sulfide ions in groundwater and wastewater can cause a foul odor to the water supplies, as well as corrosion issues when these waters enter pipelines. Additionally, when sulphide ions enter more acidic water, hydrogen sulphide, which is a toxic product even when present at low levels, can form.
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The determination of the concentration of sulfide ions in water was performed by obtaining a direct measurement using an Ag/S ion-selective electrode according to ASTM D4658.
Prior to analysis, samples must be preserved, as sulfide is a highly volatile chemical. For 100 mL water 200 µL c(Zn(C2H3O2)2) = 2.0 mol/L (equivalent to 128 mg/L S2-) and 50 µL c(NaOH) = 6.0 mol/L is added.
A volume of 50 mL of the water solution was then pipetted into a sample beaker. Immediately prior to the measurement, a 50 mL volume of SAOB is automatically added and the solution is stirred vigorously 15 seconds. Following a 3-minute waiting period, the electrodes are then placed into the sample solution and the sulfide concentration is measured without stirring.
Configuration
| 867 pH module |
2.867.0010 |
| 814 USB Sample Processor (1T/2P) |
2.814.0020 |
| 800 Dosino |
2.800.0010 |
| 741 Magnetic stirrer |
2.741.0010 |
| Dosing unit 50 mL, (SAOB) |
6.3032.250 |
| Sample rack, PP, 22x 120 mL |
6.2041.470 |
| Sample beaker, PP, 120 mL |
6.1459.300 |
| Titration head, 3x NS 14 |
6.1458.040 |
| Ion-selective electrode, Ag/S |
6.0502.180 |
Ag/AgCl reference electrode; Inner electrolyte c(KCl) = 3 mol/L,
Bridge electrolyte c(KNO3) = 1 mol/L (pH = 13.5) |
6.0726.100 |
| Pt 1000 temperature sensor |
6.1110.100 |
| Electrode cable 2 m / F |
6.2104.030 |
| Strand / 2 m / 2 x B |
6.2106.060 |
| Electrode cable 2 m, 2 x 2 mm |
6.2104.150 |
| tiamoTM 2.5 |
6.6056.252 |
Solutions
| SAOB |
Sulfide anti-oxidant buffer, c(NaOH) = 2.0 mol/L, c(ascorbic acid) = 0.2 mol/L, c(EDTA) = 0.2 mol/L, if possible this solution should be bought from a supplier. |
| Zinc acetate solution |
c(Zn(C2H3O2)2) = 2.0 mol/L, if possible this solution should be bought from a supplier. |
| Sodium hydroxide |
c(NaOH) = 6.0 mol/L, if possible this solution should be bought from a supplier. |
Parameters
| Mode |
MEAS Conc |
| Stirring rate |
Off |
| Signal drift |
1 mV/min |
| Min. waiting time |
200 s |
| Max. waiting time |
1000 s |
| Measuring interval |
2 s |
| Stop signal |
Off |
Results
| . |
. |
| Sulfide concentration (n = 5) |
s(rel) / % |
| 237 mg/L |
0.8 |
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This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.
For more information on this source, please visit Metrohm AG.