Sulphide ISE Reagent Prep
Sulphide Standards and Anti-Oxidant Buffer Preparation.
Sodium Sulphide standard solutions can be prepared from reagent grade Sodium Sulphide Hydrate Na₂S.9H₂O). It is advised that all Sulphide solution preparation be performed in a fume hood to avoid breathing Noxious fumes.
Sulphide standards have to be prepared fresh prior to analysis as they are volatile. We have prepared a guide on how to prepare and preserve Sulphide standards and samples to ensure that the analysis can be performed accurately. It is necessary to carry out the procedures in a laboratory.
Stock Standard Preparation.
Precise standards cannot be prepared by weighing the salt because of the large and variable mass of water of Hydration. Instead prepare Saturated Sodium sulphide solution by adding approximately 100g of the reagent grade Sodium Sulphide Hydrate to
approximately 100ml of deionised water. Shake well and stopper securely and allow to stand overnight.
SAOB preparation.
Sulphide Anti-Oxidant Buffer (SAOB) can be prepared by adding 80g of reagent grade NaOH pellets to 600ml of deionised water in a 1000ml beaker. Then add 35g of Ascorbic Acid and 67g of Disodium EDTA. Stir until everything dissolves and transfer the solution to a 1000ml volumetric flask. Dilute to the mark with deionised water.
To prepare stock sulphide solution pipette 1ml of the saturated solution into 50ml of SAOB and dilute to 100ml in a volumetric flask.
Standardization.
The concentration of stock Sulphide solution must be determined by electrode titration (3225 Sulphide combination ISE) before constructing a calibration curve. Use a titrant of known concentration of either Lead Perchlorate or 0.1 M Cadmium Nitrate.
Take 50ml of stock Sulphide solution, add this to 25ml SAOB and 25ml deionised water and titrate using the 3225 Sulphide combination ISE with either of the titrants mentioned.
Calculation.
The concentration of Stock Sulphide Solution in mg/L is obtained by multiplying the volume of titrant used by 64.
When preparing standards and samples for calibration or measurement add 50ml of SAOB to every 50ml of standard or sample.
Sample preservation.
As a precaution when samples are collected the addition of 4 drops of 2M Zinc Acetate and 1 drop of 6M NaOH to 100ml of sample in a sealed bottle will prevent the loss of volatile Hydrogen Sulphide.
