The Analysis of Phosphate, Arsenate, and Silicate by Reverse Phase Liquid Chromatography

摘要

The separation of 12-Molybdoarsenic Acid (12-MAA), 12-molybdosaicic Acid (12-MSA) and 12-molybdophosphoric Acid (12-MPA) by a disposable commercially available SEP-PAK(tm) C18 reverse phase liquid chromatography column is described with UV-visible detection. The mobile phase is an acetonitrile-water solution which is 0.050 F in HCIO4and 0.016 F in MoO4−2. In these solutions lowering the acetonitrile concentration to 10.0% (v/v) inhibits the formation of 12-MAA while allowing the formation of 12-MPA and 12-MSA resulting in the retention of 12-MPA and 12-MSA upon infusion through a SEP-PAK C18 column. The arsenate anion remains in the column effluent. 12-MSA is eluted from the column by 3.0 ml of a solution which is 25.0% in acetonitrile, 0.060 F in HClO4and 0.016 F in MoO4−2and the 12-MPA is eluted from the column by 3.0 ml of a solution which is 55.0% (v/v) in acetonitrile, 0.060 F in HCIO4 and 0.016 F in MoO4−2. The column effluent which contains AsO4−3is then brought up to 35.0% acetonitrile to allow the 12-MAA to form. This solution is injected into a SEP-PAK column and the 12-MAA eluted by 3.0 mi of a solution which is 55.0% (v/v) in acetonitrile, 0.060 F HCIO4and 0.016 F in MoO4−2. The absorbance of each of the separated 12-MAA 12-MPA and 12- MSA solution are measured by a UV-visible spectrophotometer (Perkin Elmer Lambda 6) at 440 nm, and related to PO4−3, AsO4−3or SiO3−2concentration by standard methods. The detection limit is 1.25 × 10−6M for PO4−3, 8.68 × 10−6M for AsO4−3and 2.86 × 10−6M for SiO3−2. The anions may be analyzed at 10 times their detection limits with relative percent standard deviations of 0.40% for PO4−3, 1.66% for SiO3−2, and 2.27% for AsO4−3An additional method is described for phosphate analysis in solutions with [PO4−3] 10−6M.