Low-level phosphorus analysis in the presence of silicate

Concerns over anthropogenic contributions to phosphate in the environment have led to a demand for the development of new and more sensitive methods of phosphate detection. We have recently succeeded in reconfiguring a standard Alpkem Flow Solution IV system to analyze low level (less than 10 ug L-1) phosphate samples using a modified version of EPA Method 365.1. By using a higher reaction temperature, longer instrument residence time and modified color-development reagents, instrument responses can be increased significantly allowing for reliable detection of extremely low levels of phosphate. However, many "real-world" environmental samples also contain appreciable amounts of. silicate, which is chemically analogous to ortho-phosphate and also forms a blue molybdate complex. Under the conditions described above, even low levels of silicate cause positive interferences during ortho-phosphate analyses. It is, therefore, important that a careful evaluation of sample matrix and instrument parameters be made in order to insure proper interpretation of phosphate analysis data.