Nitrate Analysis-A Laboratory Experiment for the Nonscience Major Course We have found the brucine method' for the detection and estimation of nit,rate in fresh water to work well as a. laboratory experiment for our nonsoience major general chemistry course. The experiment,, which is colorimetric, involves the simultaneous preparation of several color standards and the color development of both an unknown and a fresh water sample brought to the lab by the student. By calor comparison the student reports n conoentration range for his unknown and sample. The experiment has generated considerable int,erest from stndent,~ becanse it ilh~stratesan applieat,iun of chemislry to the investigation of a pollution problem. Nit,ritte has appeared in ground waters as a result of increased use of nitrogen fertilizers. This nitrste constitutes a. health hazard in our drinking water because of intestinsl bacterial action which converts it to nitrite.2 Hemoglobin reacts with nitrite with s. resulting loss of its oxygen transporting abi1it.y. The maximum public health limit is 10 ppm nitrogen as nitrate. Students have tested well waters in farming areas and also run off waters from fertilized land. Reagents:A 100 ppm nitrogen as nitrste stock solution is prepared by dissolving 0.607 gNaN08/Iof distilled water. Suitable s t a n d a d concentrstions for color comparison are 0, 3, and 10 ppm. The latter two are made by dilution of the 100 ppm stock solution. Suitable nnkuown concentrations are 2,6, and 30 ppm, also prepwed by dilution. The brucine solution is prepared by dissolving 2 g of brucine sulfate8 in 100 ml of distilled water contsining2.5 ml of concentrated sulfuric acid. (Brucioe sulfate can be purchased for as low as 63.50 per 10 g.) A 55% sulfuric acid solution is prepared by adding 55 ml of concentrated H2S0, to distilled water bringing (he findvolume to 100 ml. Procedure. Clean five 15 X 125 mm test tubes, rinse with distilled water, and invert to drain. Transfer a 1-ml sample of dist,illed water, 3 ppm standard, 10 ppm standard, unknown, and student sample t r , the respective five test tubes. To each add 1 ml of bmeine solution and 5 ml of 55% sulfurie acid. (Droppers with 1 ml bulbs and 10 ml graduated cylinders are suitable for these transfers.) Mix the test tube solutions well and place tho tubes simnltaneously in a 600-ml beaker of gently boiling water. Remove them together after 7 min of heating, cool in an ice bath, and place in a, test tube rack for comparison of the yellow colors. If color comparisons are made immediately, the cooling step can be omitted. By comparing calor intensities decide if the unknown and water sample contain Less thau 3 ppm nitrogen, between 3 and 10 ppm nitrogen, or greater than 10 ppm nitrogen. Compare t,he cnkx intemities by holding a. piece of white paper behind the test tubes. The weaker intensities can be compared by looking down intu the lest tubes held over white paper. 110 not compare the samples with those of other students as there are variations in the colors due t a differences in het~ting. There is some variation in color intensities produced by the brucine reaction. By treating the standards and 1111knowns simultaneouuly, however, this problem is circumvented. A better guide to the time needed for color development is t,he distribution'of intensibies. Further herttine ran he wed if eolora are t,ou faint.. Faint colors indicate that discoloration of this solution occurs on standing.
'FISHER, F. L., I ~ TE. R., , AND BECKMAN, H. F., Anal. Chem., 12, 1970 (1958). a ScientificAmerican,220,48 (1969). 'CAUTION: While brucine sulfate is less toxic than brucine, extreme caution should he observed in handling thin material.
Volume 48, Number 10, October 1971
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