Description
The UV600TPTN is an on-line water analyser to simultaneously measure total phosphorus and total nitrogen based on a wet-chemical oxidation in compliance with EN ISO 6878 and Standard Methods 4500-P, 4500-N and 4500-NO3. It belongs to a family of analysers for total parameters: TP (Total Phosphorus), TN (Total Nitrogen) and TOC (Total Organic Carbon).
Tethys Instruments UV600TPTN provides a simple and fast way to measure total phosphorus and total nitrogen for surface water or industrial / municipal waste water treatment plants with accuracy, stability and low operating cost. A digestion set up enables to oxidize both organic and inorganic phosphorus and nitrogen compounds into orthophosphates and nitrates, respectively, using potassium persulfate under alkaline conditions at 95 ͦC and UV light irradiation. Total amount of orthophosphates is then quantified by a colorimetric module while total amount of nitrates is determined by direct UV absorbance measurement. Phosphorus compounds such as trimethyl phosphate or polyphosphate (sodium hexametaphosphate) can be recovered up to 98% yield. External probes can be added for phsysicochemical parameters like pH, ORP, dissolved oxygen, conductivity and total suspended solids. Thanks to its automatic cleaning system, the maintenance is roughly limited to the periodic refill of the inexpensive cleaning solution and regents.
- The water sample is mixed with an alkaline decomposition solution made of potassium peroxodisulfate. The solution is heated at 95 °C and irradiated with UV light. Phosphorous compounds are converted to orthophosphates while nitrogen-based compounds are transformed to nitrates. Two different methods are used to quantify orthophosphates and nitrates.
- The water sample is mixed with an alkaline decomposition solution made of potassium peroxodisulfate. The solution is heated at 95 °C and irradiated with UV light. Phosphorous compounds are converted to orthophosphates while nitrogen-based compounds are transformed to nitrates. Two different methods are used to quantify orthophosphates and nitrates.
- In the molybdenum blue method (EN ISO 6878 and Standard Methods 4500-P), the orthophosphate ions react with ammonium molybdate and potassium antimonyl tartate under acidic conditions to afford phosphomolybdic acid. This acid is then reduced by ascorbic acid to give a colored molybdenum blue, which intensity is measured by a LED at 630 nm.
- In the vanadomolybdophosphoric method (Standard Method 4500-P), orthophosphates react with ammonium molybdate under acidic conditions to afford molybdophosphoric acid. The molybdophosphoric acid reacts with ammonium monovanadate to give vanadomolybdophosphoric acid. This acid is yellow. The absorption of the solution is measured by a blue LED. In this method, the reagent has a longer lifetime than the reagents of the molybdenum blue method.
- In both methods, the absorption is proportional to the phosphate concentration, based on the Beer-Lambert law. The colorimetric module has been specially developed to reach a very small volume flow cell that reduces the quantity of reagent to preserve the environment and to reduce the operating cost. The multi-wavelength LED source assumes a colour and turbidity compensation with an unlimited life time.
- The overall measurement typically takes 14 minutes. It can be extended up to 20 minutes for more complex samples (longer digestion time needed). The oxidation yield was tested on different phosphorus compounds such as trimethyl phosphate and sodium hexametaphosphate (polyphosphate).
- A transparent screen with a reflective part enables an instant visual control of the set-up while maximising the UV irradiation of the digestion cell and protecting the user from UV light exposure.
- The UV lamp used in the digestion process can last from 6 months to 2 years, depending on the frequency of the measure.
- All wet and electronic parts are separated within the analyser.
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