|MadSci Network: Chemistry|
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 preformed. 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 !!
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