Turbidimetric determination of orthophosphate in digested plant material by flow-injection analysis

A simple, fast, and low-cost flow-injection system is proposed for the determination of orthophosphate in digested plant material. The determination is based on the precipitation reaction of orthophosphate with 0.05 mol L⁻¹ zinc solution in 0.05 mol L⁻¹ triethanolamine buffer (TEA/TEAH⁺, pH 6.0) solution containing 0.025% (w/v) poly-(vinylalcohol). The zinc orthophosphate suspension produced was directly measured at 410 nm. Under the best experimental conditions, orthophosphate was determinated in the concentration range from 5 to 60 mg P L⁻¹, and the relative standard deviations were less than 1.6% for 10 and 20 mg P L⁻¹ solutions (n = 9). The analytical frequency was 180 h⁻¹. The results obtained using the proposed FIA procedure and those obtained using a standard spectrophotometric procedure agree at the 95% confidence level. © 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:236–240, 2000