*2.3.3 Preparation of solutions*

The stock solution of formaldehyde with of 1000 mg. L<sup>−</sup><sup>1</sup> was prepared using 2.7 ml of 37% (v/v) formaldehyde solution diluted with distilled water in a 1000 ml volumetric flask. An aqueous solution of chromotropic acid (CA) 5% (w/v) was prepared, dissolving 1.25 g of solute with distilled water in a 25 ml volumetric flask. An aqueous solution of magnesium (MgSO47.H2O) 60% (w/v) was prepared, dissolving 60 g of solute with distilled water in a volumetric flask 100 ml.
