MadSci Network: Chemistry

Re: Nitrate in water Lab test ?

Date: Mon Aug 2 09:51:16 1999
Posted By: David Sherman, Staff, Sr. Analytical Chemist, Chr. Hansen Ingredient Technology
Area of science: Chemistry
ID: 932535900.Ch

     There are two different types of results in an Analytical Chemistry 
Laboratory, Quantitative and Qualitative.  Quantitative nitrate analysis 
will provide the analyst with an actual concentration of nitrate present 
in the water.  The drawback for you is that this procedure requires costly 
instrumentation (spectrophotometer or ion chromatograph) and is usually 
only performed in a laboratory because of the expense.  Another 
alternative quantitive procedure that you mentioned in your question is 
test kits.  These kits can be purchased for about twenty to thirty US 
dollars (30 test per kit) and are based on colorimetric testing.  I did 
find a supplier for these types of test kits in Auckland, NZ.  The name of 
the company is "Scientific Suppliers, Ltd." and the telephone number is 64 
9 274 0267 (there are international area codes that you should ignore.)  
The person that you should speak with is Hugh Blank.  I would tell Mr. 
Blank that he was referred by "VWR Scientific Products" in the US.  I 
would also explain your problem to Mr. Blank and ask if his company would 
like to donate some test kits to your school and possibly get his 
company's name and his picture in a local paper.  That takes care of 
quantitative analysis. 
     A qualitative result only determines the presence or absence of 
nitrate in the water sample.  I was able to find a qualitative procedure 
for nitrate analysis in College Chemistry with Qualitative Analysis, 5th 
Edition by Nebergall, Schmidt, and Holtzclaw.  First I must caution you 
that the reagents and chemicals used in the method are DANGEROUS, if used 
incorectly.  Appropriate safety procedures and devices like safety 
glasses, a hood, lab coat, and gloves, just to name a few, should be 
followed.  The method uses Iron(II) sulfate and dilute sulfuric acid.  
"The reduction of the nitrate ion (NO3-) to nitric oxide (NO) by iron(II)
(Fe+2) takes place rapidly only in a solution of very high hydrogen ion 
(H+) concentration and at relatively high temperatures, conditions which 
prevail at the interface of the two liquids," College Chemistry with 
Qualitative Analysis, 5th Edition by Nebergall, Schmidt, and Holtzclaw.  
Nitrite (NO2-), bromide (Br-) and iodide (I-) ions will interfere with the 
identification and must be "cleaned up" before the nitrate analysis can be 

Procedure 1:  ID of NO3- in the absence of NO2-, Br-, and I-.  "Add five 
drops of sample into a test tube (TT) and 4 M sulfuric acid (H2SO4)
dropwise until the solution is acidic.  Now add 5 drops of freshly 
prepared 0.1 M Iron(II) sulfate (FeSO4) solution.  Add 5 drops of 18 M 
H2SO4, holding the TT in an inclined position so that the H2SO4 may run 
down the side of the TT and form a seperate layer on the bottom of the 
tube.  If the NO3- is present a brown ring will form at the junction of 
the two liquids, within a few minutes."

Procedure 2:  ID NO3- in the presence of NO2-.  "Removal of the NO2-.  To 
six drops of sample in a TT add 4 drops of 1 M (NH4)SO4 solution.  Place 
the mixture in a watch glass and slowly evaporate the solution until only 
a moist residue remains (do not evaporate to dryness.)  Add 4 drops of H2O 
and evaporate to a moist residue a second time.  Dissolve the residue in 
10 drops of water and transfer the mixture to a small TT.  Proceed with 
procedure 1 for NO3- analysis."

Procedure 3: ID NO3- in the presence of Br- and I-.   "Removal of the Br- 
and I-.  To 6 drops of sample in a TT add 10 drops of water.  Acidify with 
4 M Acetic acid and the add 80 mg of powdered, NO3- free, silver sulfate 
(Ag2SO4.)  Stir and grind the mixture in the TT for 2-3- minutes.  
Separate the precipitate and transfer the solution to a TT.  Proceed with 
procedure 1 for NO3- analysis."  

All three procedures taken from College Chemistry with Qualitative 
Analysis, 5th Edition by Nebergall, Schmidt, and Holtzclaw.  

Good Luck in the Lab !!                   

Current Queue | Current Queue for Chemistry | Chemistry archives

Try the links in the MadSci Library for more information on Chemistry.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-1999. All rights reserved.