Analytical Procedures - Arsenic in Waste Water
February 11, 2002

Introduction Equipment Reagents Procedure Spectrometer Determination

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Introduction

There are a few methods to analyze arsenic in waters, but the fastest and most reliable method is by Atomic Absorption (AA) technique as volatile hydride. The sample is oxidised to arsenic (V) with potassium persulphate and sulphuric acid, because in this oxidation form, the volatile hydride of the element produces a more time constant signal.   The reduced form As(III) produces a stronger but more random signal.

Equipment

• Atomic Absorption spectrometer equipped with volatile hydride system (VHE)
• Water bath heater
• 250 ml Erlenmeyer flask
• 100 ml flask
• 250 ml plastic bottle

Reagents

 

• Aqua regia solution
• Sulphuric acid concentrate
• Potassium persulphate grade reagent
• Arsenic(V) standard solution

Procedure

Pour 100 ml of water sample in a 250 Erlenmeyer flask, add 0.2 g. of potassium persulphate and 0.2 ml of sulphuric acid.  Heat on the water-bath for about 90 minutes to allow all the arsenic to oxidize to As(V).  Let the sample cool and then pour in it into a 100 ml flask and add water up to the mark. The solution is ready to be analysed in AA by hydride evolution system.

Spectrometer Determination

If possible use a double beam spectrometer equipped with an automatic VHE system, like the Perkin Elmer M/HS 20 or FIA one.

Put 1 ml of the sample into the VHE system, add the proper solutions, as recommended by the instrument instruction manual and read the absorption peak (or directly concentration) at 193.7 nm.  Determine the As concentration against a previously defined calibration curve.