Ortho-Phosphate

This method is used for the determination of ortho-phosphate in water and wastewater. The EPA range of this method is 0.01 to 1.0 mg/L as Phosphorus. However, this method is also applicable to other ranges.

Summary

Ortho-phosphate reacts with molybdenum (VI) and antimony (III) in an acid medium to form a phosphoantimonylmolybdenum complex. This complex is subsequently reduced by ascorbic acid to a heteropolyblue with an absorbance maximum at 660 nm or 880 nm.

Interferences

Ferric iron up to 70 mg/L, copper up to 10 mg/L and silica up to 10 mg/L do not interfere. Filter turbid samples prior to analysis.

Availability

System	Method #	Range(s)
Flow System	A203	0.002-0.5, 0.02-2, 2-50, 10-1000 µg/l as P
Astoria 2	A203	0.002-0.5, 0.02-2, 2-50, 10-1000 µg/l as P
rAPID-T	D203	0.02-2.0 mg/l as P

Ortho-Phosphate in Sea Water

This method is used for the determination of ortho-phosphate in seawater and is applicable to many ranges.

Summary

Ortho-phosphate reacts with molybdic acid to form phosphomolybdic acid. This complex is subsequently reduced with hydrazine to phosphomolybdous acid. Absorbance is measured at 820 nm.

Limitations

Turbid samples must be filtered before determination. Samples with background absorbance at the analytical wavelength may interfere.

Availability

System	Method #	Range(s)
Flow System	A204	0.06-3.0 µM o-PO
Astoria 2	A204	0.06-3.0 µM o-PO
rAPID-T	N/A