Determination of Condensed Phosphates of Low Concentration in Water by Liq uid Chromatography

Abstract

The analytical process of ortho-, pyro- and triphosphates of low concentration in water was investigated by the anion exchange chromatography using post-column method. The mixed solution prepared for ASTM D 515-72 without antimony potassium tartrate wcs used as a color-producing agent.
In the proposed method, the hydrolysis of conden sed phosphates in a PTFE-type valve loop injector as found to be avoided by the use of a stainless-steel-type one. Furthermore, the adsorption of colored molybdophosphate complex on the PTFE tube in the chromatographic system and the drift of its base line were found to be avoided by mixing the reaction mixture with sodium dodecyl sulfate solution at the outlet of the reaction bath.
The recommended conditions for analysis were as follows; column: 8 mm I. D. × 140 mm glass column, eluent: 0.25 mol·dm^-3 sodium chloride solution containing 1.5 mmol·dm^-3 EDTA, column temperature: 30°C, color-producing agent: above mentioned one, flow rate of eluent: 0.84 cm³· min^-1, flow rate of eluate from column delivered to detection system: 0.42 cm³min^-1, flow rate of color-prod-ucing agent: 0.21 cm³· min^-1, flow rate of 1.5% sodium dodecyl sulfate solution 0.16 ³· min^-1, reaction coil: 1 mm I. D. × 10 m, reaction bath temperature: 95°C, sample size: 2.0 cm.
The quantitative analysis of each condensed phosphate was attained by the proposed method and its detection limit was O.05 mg P. dm-3 for the measurement of peak area and 0.01 mg P. dm-3 for peak. height in chromatogram. This method was applied to various waters containing sewage and compared with ASTM method (D 515-72) for phosphorus in water (Table 3). The results obtained were satisfactory except for sea water.