Total Nitrogen/30

Test Method Technical Information


Tests For: Total Persulfate Nitrogen in Natural and Wastewater
Test Range: 0–30 mg/L N
Reagent Chemistry Used: Alkaline persulphate digestion, chromotropic acid
Method Detection Limit*: 1.21 mg/L
Limit of Quantification**: 3.84 mg/L

*The Method Detection Limit (MDL) is defined as the minimum measured concentration of a substance that can be reported with 99% confidence to be different from the method blank results.
**The Limit of Quantification (LOQ) is the smallest quantity that can be detected with reasonable certainty for a given analytical procedure.

Testing for Total Nitrogen

Total nitrogen is a vital test for assessing the quality of effluents and wastewater prior to discharge. In the UK the Urban Wastewater Treatment Regulations (1994) make provision for the control of discharge of total nitrogen to sensitive bodies of natural water. The monitoring of the rate of nitrogen removal is therefore of great importance in wastewater treatment. Total nitrogen is composed of nitrate, nitrite, ammonium, and organic nitrogen compounds. The Palintest Tubetests Total Nitrogen/30 test provides a simple method of measuring total persulfate nitrogen over the range 0–30 mg/L N.

Reagent Chemistry

The Palintest Tubetests Total Nitrogen/30 test is a two-stage procedure. The sample is initially digested with alkaline persulfate to break down nitrogenous compounds which are then converted to nitrate. The digested sample is then transferred to a Palintest Tubetests Nitrate/30N Tube for determination of the total nitrogen present. The reagents are provided in the form of pre-dispensed tubes and powders. The powders are added using a specially designed scoop and funnel.

The intensity of the colour produced in the test is proportional to the total nitrogen concentration and is measured using a Palintest Photometer.

In total nitrogen determinations, the recovery of different compounds depends to an extent on the method of oxidisation used to make the conversion to nitrate. It is normal practice to refer to the method of oxidisation when stating test results for any formal purpose. Results from the Palintest Total Nitrogen test should therefore be expressed as ‘Total Persulfate Nitrogen’.

Best Practice Advice for Testing

  • The Palintest Tubetests Total Nitrogen/30 test is a simplified laboratory procedure and should be carried out in accordance with good laboratory working practice.
  • The Total Nitrogen Tubes contain sodium hydroxide solution, to which potassium persulfate is added. The Tubetests Nitrate/30N Tubes contain strong sulfuric acid. These reagents must be handled with care. The use of appropriate protective clothing, gloves and safety spectacles is recommended. In the event of skin or eye contact, or spillage, wash immediately with large amounts of water.
  • Care should be taken when adding Tubetests Total Nitrogen Reagent No 2 to the digestion tubes. Sulfur dioxide will be evolved. Care should be taken when opening the Tubetests Nitrate/30N Tube which contains concentrated acid. On adding the digestate heat will be produced, the tube will become hot, and gases may be evolved.
  • It is generally recommended that the test be conducted in a fume cupboard where available, particularly in the case of samples originally known to contain toxic materials such as cyanide or sulfide
  • The method, in general, does not yield 100% recovery. Recoveries of various nitrogen compounds have been tested in the Palintest laboratories. Inorganic compounds such as potassium nitrate, sodium nitrite and ammonium chloride yield in excess of 95% recovery. The typical recoveries of some organic nitrogen compounds are quoted below:
Compound Typical Recovery
Glycine 95% all levels
Urea 95% all levels
Nicotinic Acid 95% at 10 mg/L, 45% at 30 mg/L
Creatinine 100% at 10 mg/L, 70% at 30 mg/L

  • Tubetests Nitrate Powder is light sensitive. Store in original pack and keep lid closed when not in use.
  • The used Tubetests Nitrate/30N Tubes contain strong sulfuric acid and other chemical reagents, and care must therefore be exercised in their disposal. The tube contents should be disposed of in accordance with the laid-down disposal procedures of the laboratory of use.

EPA, Definition and Procedure for the Determination of the Method Detection Limit, Revision 2, Dec 2016.
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the “Gold Book”).