TP - Total Phosphorus

Phosphorus is an essential nutrient of plant, animal and human. In water, it exists primarily as orthophosphate (PO43-) or in organic compounds. The parameter total phosphorus (TP) defines the sum of all phosphorus compounds that occur in various forms. The determination is defined of the German Institute of Standardization (DIN EN ISO 6878:2004-09).

Need of monitoring

Increased phosphorus concentration leads to the eutrophication of the aquatic environment. Impacts are oxygen deficiency with deadly consequences to fish and other aquatic organisms.

This results in the need of monitoring this parameter. Phosphorus can pass via waste water discharges or drainage of agriculture areas into the waters. In addition, nowadays detergents are often used for e.g. dishwashers that contains phosphorus. Their increased usage and disposal leads to increased concentrations in the waste water. With the expansion of waste water treatment plants with phosphorus elimination the pollution that occurs from waste water discharges, sustainably reduced.

Measurement methods

Phosphorus compounds can be determined by various colorimetric methods, which involve different advantages and disadvantages. In addition, there is a difference beteen the parameters be determined in the dissolved phase (orthophosphate PO43-) or by including the solids (total phosphate). For determination in the dissolved phase are used the molybdenum blue method or the vanadate/ molybdate method (yellow method). The molybdenum blue method is more accurate in the lower measuring ranges. Hence, these methods are used differently. Depending on the application, importance of accuracy, DIN-conformity or profitability.

Molybdenum blue method

The TP value can be determined by the molybdenum blue method, by adding a reducing agent. This can take place as follows:

Orthophosphate reacts with ammonium molybdate to a slightly yellow molybdenum phosphoric acid. By adding a reducing agent, the molybdenum blue is formed, which has a blue color:

PO43- + 12 (NH4)6Mo7O24 + 3H+ →  H3P(Mo3O10)4

H3P(Mo3O10)4 + 2 SnCl2 + 8 HCL →  H7P(Mo3O10)4 + 2 H2 (SnCl6)

Subsequently the TP value can detect from the molybdenum blue. Its intensity of the colour determined with a photometer at wavelengths of about 500 - 750 nm. This method is particularly suitable for the determination of low concentrations.

The QuickTOCNPO also uses the advantages of this method and measure the TP by adding the oxidant persulfate. Then the sample mixture flows into a UV reactor. There the oxidation of the sample proceeds by ultraviolet light. Molybdenum blue is formed and the result of TP detects by using a photometer.

Vanadate yellow method

Here a reaction occurs to the orthophosphate ions with ammonium molybdate and ammonium vanadate. The result is the yellow Ammoniumphosphorvanadomolybdat, which is also determined photometrically by its intensity of the colour.

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The total organic carbon (TOC) is one of the most important sum parameters in the assessment of the organic pollution of water. Since it includes all carbon compounds as one mass, it is exactly defined and an absolute quantity. Therefore, it may be determined directly.

Read more about TOC measurement methods.

Total organic carbon analyzers of LAR Process Analysers AG

The chemical oxygen demand (COD) indicates the amount of oxygen which is needed for the oxidation of all organic substances in water and is thus an important indicator for water analysis. It is considered in the planning and controlling of treatment, as well as assessing its efficiency, thus forming the basis for the calculation of waste water charges.

The COD can be determined in laboratory or online, whereby these methods significantly differ in duration and consumables used.

Read more about COD measurement methods.

COD analyzers of LAR Process Analysers AG

The biochemical oxygen demand (BOD) indicates the amount of oxygen which is needed for the biological degradation of organic substances in water.

Since the generally used BOD5 excludes the nitrification part of the process, this parameter is poorly suited for the control of waste water treatment plants. Alternatively, the total BOD is well-suited, due to the determination of the nitrogen as well as the carbonaceous part of biological degradation.

Read more about the online measurement of BOD.

Toxicity is described as the direct harmful effect of a substance on organisms. These effects can already occur at low concentraions of toxic substances and are dependent on the incubation period and the dosage.

Some test methods that are available on the market can detect toxicity by using fish, daphnia, molluscs, algae or luminous bacteria and testing whether a water sample has a toxic effect on the organisms. They do not, however, identify exactly which toxins are present.

Read more about online toxicity measurements.

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The total nitrogen bound (TNb) shows the pollution of water caused by nitrogen compounds. Nitrogen may be present as ammonia, ammonium salts, nitrites, nitrates and organic nitrogen compounds.

In contrast to single measurements of the above-mentioned components, the TNb determination contains all these substances in a single analysis process.

Read more about online TNb measurements.

The total phosphorus (TP) is a sum parameter that shows the organic and inorganic phosphorus compounds in water. Phosphorus is an essential nutrient for humans as well as flora and fauna. However, the substance – depending on its concentration– may cause serious damage.

Read more about online TP measurements.

TN TP analyzer of LAR Process Analysers AG