Iron in spinach is determined by grinding the spinach, digesting in acid, filter

Question

Iron in spinach is determined by grinding the spinach, digesting in acid, filtering and neutralizing the resulting solution, and reacting it with a complexing agent in order to form a clear, colored product. Spectrophotometry is used to measure the absorption of the product, and several replicates measurements are made from aliquots of the final product. Which is a potential source of imprecision in the replicate absorption measurement? The solution was not filtered well and is a little bit cloudy. The analyst does not measure a solvent blank. The cuvette is inserted into the spectrophotometer in different orientations for each measurement. The cuvette is filled with different volumes of solution each time, but always is filled at least 2/3 of the way up, above the height at which the light beam passes cuvette.

Explanation / Answer

In an absorption meaurement experiment for the detection of iron in a sample, the potential source of imprecision comes from,

a. The solution was not filterted well and is a bit cloudy.

The insoluble particulates in solution would diffract the incident beam each time differently and the amount of light absorbed each time would be thus different resulting in different values for absorption and hence the amount of Fe in solution.

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