Spectrophotometric Determination of Calcium and Magnesium in Pure Alumina with P&R and EBT after Selective Extraction of the Matrix with Tri-n-butyl Phosphate

A spectrophotometric method for the determination of calcium and magnesium in pure alumina has been developed. The method involves extraction of aluminium with tri-n-butyl phosphate (TBP) at pH ∼ 4.3. Magnesium and calcium are then determined in aqueous solution at pH ∼ 7.80 and at pH ∼ 12 using eriochrome black T (EBT) and P&R as metallochromic indicators at 540 and 560 nm respectively. The method obeys Beer's law from 0.2 to 3.0 μg MgO/ml and 0.2 to 4.0 μg CaO/ml respectively. Traces of titanium (if present) are effectively masked with triethanol amine (TEA), but traces of iron (if present) are extracted with aluminium. The interferences of Co, Ni, Cu and Mn can be avoided by masking with KCN. The method has been applied to synthetic and various pure alumina samples.