Measurement of phosphate in small samples using capillary electrophoresis with laser-induced luminescence detection

A capillary electrophoresis-based method was developed for the detection of phosphate in small samples. Phosphate was incubated in buffer with 50 μM Eu3+-tetracycline to allow for the formation of the luminescent Eu3+-tetracycline-phosphate complex. The complex was separated from the excess Eu3+-tetracycline, which is also luminescent, and the complex detected by post-column laser-induced luminescence within a sheath flow cuvette. Separation time was <90 s with a total run time of 5 min. No flushing of the capillary was required between runs. Phosphate standards ranging from 10–200 μM were analyzed. Increasing the concentration of Eu3+-tetracycline increased the linear range but at the cost of a decreased sensitivity. A decrease in the Eu3+-tetracycline resulted in an increase in sensitivity down to 5 μM but a decrease in linear range. As an application, the phosphate content of a milligram sample of soil was determined to be 0.51 ppm.