Fosfatkoncentration

Fosfatkoncentration, or phosphate concentration, refers to the amount of phosphate ions present in a solution. Phosphate in aqueous solutions exists mainly as the anions H2PO4− and HPO4^2− at near-neutral pH, while PO4^3− becomes more prominent at higher pH. The distribution among these species is governed by the acid–base equilibria of phosphoric acid, with pKa values around 2.15, 7.20, and 12.35.

Concentrations are typically expressed in molarity (moles per liter) or in mass per volume, such as milligrams per liter (mg/L). In water-quality and agronomy contexts, phosphate is often reported as mg/L as PO4-P (phosphorus in the phosphate form). To convert to mg/L as PO4, a factor of about 3 is commonly used, recognizing that the exact factor depends on the species measured.

Measurement methods commonly rely on colorimetric assays based on the ammonium molybdate reaction, forming a phosphomolybdate complex that is reduced to a blue color for quantification (often referred to as molybdate blue or the ascorbic acid method). For total phosphorus, a digestion step is used to convert organic and particulate phosphorus to orthophosphate before measurement.

Applications and relevance include environmental monitoring of water bodies to assess eutrophication risk, compliance with regulatory limits, and studies of soil and plant phosphorus status. In biological systems, phosphate concentration relates to intracellular pools such as ATP, nucleotides, and phospholipids.

Interferences can arise from silicates or other reagents in colorimetric assays, and proper sample preservation, digestion, and calibration are essential for accurate results.