Question

You are analysing Ca levels in the Canning River using atomic emission spectroscopy. When taking your samples you notice a large microalgal bloom nearby suggesting the presence of a large amount of phosphate in the river. Explain if the phosphate will have an effect on your analysis and, if so, what steps can you take to deal with this?

Answer 1

Phosphate (PO₄^3-) forms a refractory compound, calcium phosphate [Ca₃(PO₄)₂] with calcium (Ca). The refractory compound is not atomized in flames and hence, reduces the concentration of Ca atoms and therefore, interferes with the measurement.

3 Ca + 2 PO₄^3- -------> Ca₃(PO₄)₂

The interference due to PO₄^3- can be removed by adding lanthanum (La) to the samples. La reacts with phosphate to form lanthanum phosphate (LaPO₄) which removes PO₄^3- from the system.

La + PO₄^3- --------> LaPO₄