Sulfide H2S Analyzer – CA900

The ECD CA900 Sulfide Analyzer is an all-in-one analyzer for the
continuous measurement of sulfide ions in aqueous media.
Sulfide is present in well water, municipal wastewater and waste
waters from refineries, tanneries, chemical plants and paper and
pulp facilities.
Hydrogen sulfide (H2S) is a gas that dissolves in water and gives
it that “rotten egg” odor. H2S exists in acidic water as a dissolved
gas, at pH values above pH 7 bisulfide ions (HS-) are the
predominate form and at very high pH values, > pH13, sulfide
ions (S-2) predominate.
The ECD CA900 uses a sulfide ion selective electrode (ISE) to
measure the total amount of sulfide present in the sample. The
measurement must be made at high pH levels where S-2 exists.
Potassium hydroxide (KOH) is added to raise the pH of the sample
to around pH 13 and a pH electrode measures the actual pH.
Sulfide and bisulfide exist in a pH dependent equilibrium with the
ratio of each dependent on the pH. The sulfide ISE measures the
sulfide present in the sample and the pH measurement infers
what percentage of the total sulfide was measured. The analyzer
calculates and displays the Total sulfide present.
The highly caustic sample is then neutralized with HCl and the pH
is measured and displayed to verify the neutralization. The
neutralization of KOH with HCl produces potassium chloride salt
(KCl) and water. The neutralized sample can be disposed of as
waste or returned to the water supply.

The ECD CA900 is a sequential sampling analyzer. It runs the
following analysis cycle; fill the measurement cell with sample
and drain, fill and drain, fill, add caustic, mix, measure S-2, adjust
4-20mA signal, add acid, mix, measure pH, adjust 4-20mA signal,
drain the flow cell and repeat the cycle. Each cycle uses about 1
ml of caustic and 1 ml of acid. The analyzer is set to run 6 minutes
analysis cycles but can easily be programmed to run 12minute or
30minute cycles. Running continuously at 10 cycles per hour, the
CA900 uses 7.2 liters of each reagent per month, at 5 cycles per
hour, 3.6 liters per month and at 2 cycles per hour less than 1.5
liters per month.
The ECD CA900 is easy to start up and maintain. First connect the
Sample feed line, reagent lines and Drain line to the analyzer.
Mount the sulfide and pH sensors in the flow cell. Next connect
the two outputs, S-2 and pH and supply power, a switched
110/220 VAC line. Prime the peristaltic pumps and start the
measurement cycle. The touch screen display and 4-20 mA
outputs will indicate the total sulfide and the neutralized pH
value. A digital display indicates the Sulfide measurement and
the 4-20 mA output values are captured in the measurement
cycle and displayed until the next measurement cycle.