Determing Sulfide in Water by ASTM D4658

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.

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

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.

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