In an experiment for measuring water hardness in a water sample, using Atomic Absorption Spectrophotometry, I obtained a value of 173.74 ppm hardness for my water sample. Using EDTA determination, I obtained a value of 440 ppm hardness for my sample. In both these methods, I was measuring the hardness in relation specifically to Mg and Ca Ions.
Considering the fact that AA Spectrophotometry is a highly accurate method for measuring water hardness, I was wondering if there could be any possible explanations as to why the hardness for water obtained through EDTA determination is greatly larger than AA hardness. I recognize the fact human error is likely whilst carrying out an EDTA determination of a water sample.
Actually there are a number of typical interference events for the EDTA water hardness test that are mentioned in the Standard Methods for Water Analysis used in Drinking Water certification by the EPA. These are also discussed in the SW846 guidance documents for RCRA analysis of ground water and soils. EDTA also picks up on K and Na in the hardness test as interferents and there are additives to suppress ...
This solution is comprised of a detailed explanation which outlines possible interferents which may result when conducting water hardness tests. This is completed in 280 words.