Question

In the concentration range of 1 to 100 μg/mL P, phosphate suppresses the atomic absorption of Ca in a linear manner. The absorbance levels off, however, between 100 and 300 μg/mL P. Explain. How can this effect be reduced.

Short answer

The addition of lanthanum or strontium ions reduces the effect of phosphate supression of Ca absorption.

Step-by-step solution

Step1. Given information

Explain how phosphate reduces the effect of suppression of atomic absorption of Ca.

Step2. Reason for suppression

Calcium phosphate, produced by calcium and phosphate ions, is difficult to volatilize. More calcium atoms are converted into calcium phosphate as the concentration of P in phosphate increases from 1 g/mL to 100 g/mL. This means that there is no absorption. However, in the case of calcium atoms, the amount decreases, resulting in a drop in absorbance. As a result, with the same calcium concentration, there is reduced absorption.

Step3. Method to reduce the suppression

The phosphate ion interference in calcium determination can be removed by adding extra releasing agents such as lanthanum ions or strontium ions. This is due to the fact that in calcium phosphate, lanthanum and strontium ions combine with phosphate ions, releasing calcium ions that can absorb radiations.