2.2. Chemicals
All solutions were prepared from L.R. grade sodium
hydroxide and distilled water. The following inhibitors and
complexing agents were used: sodium citrate (Ranbaxy G.R.
grade); sodium stannate (Loba Chemie G.R. grade), and
calcium oxide of high purity grade (B.D.H). The calcium
oxide was ignited for a long time to decompose any calcium
carbonate contained in the sample; it was then cooled and
stored in a desiccator prior to use.