Answer to Question #69572 in General Chemistry for amir

Question

How to prepare a water sample for photometry

The purpose of measuring N P K Ca Mg S is to determine the amount of material consumed by different types of plants in different periods.

The problem occurs when the initial solution of humic acid and fulvic acid is added. In this case, the water released is very dark and it is not possible to use this water in photometry.
I have searched a lot, but the easiest way is to use photometer and chemical reagents to measure the concentration of the material.
Due to the fact that the error of 10-15% is acceptable in test conditions, it is thought to isolate humic and fulvic acids to clear water without changing the concentration of other materials.

Answer 1

The problem with humic acid is that it forms complexes with Ca, Mg, Fe and it actually contains nitrogen. Thus, you will not be able to found all this elements in the plant. First you need to destroy your sample some how. But destruction must be done in a completely closed vessel. In fact, you need to transform all complicated molecules into something very simple. Then try to dissolve all destruction products in some strong mineral acid or melt it with KOH or NaOH and analyse it in this form. However, the best solution is to use automatic element analyser. Of course, if you have it.