I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
446
Ayers and Clewell, Paint, Oil,Chem. Rev.,100, N o . 3, 7-8, 30-2. 42 (1938).
Bruce, H. B., Bur. Standards Tech. Paper, 306 {1926). Davidsohn, A., Paint Manuf., 9, 340 (1939). Davis, D. S., “Empirical Equations and Nomography,” pp, 4-7, 24-6, New York, hfcGraw-Hill Co., 1943. Federal Standard Stock Catalog, Spcc. TT-P-23a, pp. 7-9 (March 22, 1940). Ibid., TT-P-Sla, p. 6 (Jan. 16, 193i). Federation of Paint and Varnish Production Clubs, Tech. Proc., DP. 27-34 (1939). Gardner, Sward, and Levy, Am. Paint Varnish hlfrs. Assoc., CP’TC. 362, 235-72 (1930). Gardner, Sward, and Levy, Metal Cleanmg Finishing, 2 , 537-8 (1930).
Hallett, R. L., Proc. A m . SOC.Testing Materials, 30, Pt. 11, 895910 (1930).
Hanatock, R. F., J . Oil Coloztr Chem. Assoc., 20, 5-34 (1937). Hanstock, R. F., and Jordan, L. A,, Research Aasoo. of British Paint, Colour & Varnish Mfrs., British Patent 434,136 (Aug. 27, 1935).
Vol. 16, No, 7
(15) Haslam, G.S.,INU.E m . CHEAI., . A s ~ r . ED.. , 2, 69 (1930). (16) Ibid., 2, 319-22 (1930). (17) Jacobsen and Reynolds, I b i d . . 6, 303-5 (1034). (18) Judd, D. B., J . Resoarch .Vutl. Bur. Standards, 19, 287 (1937). (19) Kuhelkaand Munk, 2. tech. Physik, 12, 593 (1931). (20) Levy, S.A., Am. Pairit Varnish Mfrs. Assoc., Circ. 377, 135-0 (1931).
Morrison, R. A., Oficial Dioest Federation Paint & Varnish Pradwtion Clubs,112, 745 (1932). Pfund, A . H., Proc. A.S.T.M., Preprint 94, 0 (1930): Ibid., 30, Pt. 11,878 (1930). Sawyer, R. H., Am. Roc. Testing Materials, Symposiuni on Color, pp. 23-37 (1941).
Sohneerson. S. L., Byull. Obmena OpUt. Lakokrasoehn. Prom., 10, 22-3 (1940). (26) Stutz and Haalam, Proc. Am. SOC.Testing Materials, 30, P t . 11, 884-90 (1930). (27) Sward, G. G., Am. Paint Varnish Mfrs. Assoc., Circ. 433, 217-18 (1943). --,(28) Sward, G. G., Natl. Paint, Varnish Lacquer Assoc., Sci. Sec., Circ. 433 (July, 1933). (29) Tichenow. E., Farben Ztg., 36, 1469-70 (1931). \ - -
Determination of Nitrate, Nitrite, and Ammonium Nitrogen Rapid Photometric Determination in Soil and Plant Extracts BENJAMIN WOLF, The G. L. F.-Seabrook Farms Raw Products Research Division, Bridgeton, N. J.
T
H E determination of soluble inorganic nitrogen fractions in plant and soil extracts is extremely useful in explaining crop growth. In a previous paper (4)a method was described for the determination of nitrate nitiogen. The present paper gives a more rapid method for determining nitrate nitrogen and in addition, proposes methods for determination of nitrite and ammonium nitrogen in the same extract.
CALIBRATION OF STANDARD CURVES. Aliquots of standard solutions are diluted with extracting solution to appropriate level and treated as in the determination of nutrients of soil and plant extracts. Photometer readings are taken using the a g propriate filter (Table I). Deflection concentration curves are drawn from the resultant data.
Table APPARATUS
Photoelectric colorimeter. The amounts of reagents and samples are based on the use of the Fisher electrophotometer. Vials (4),stirring rods, Waring Blendor, balance, oven, and 1- and 5-ml. pipets. REAGENTS AND SOLUTIONS
All reagents should be of C.P. grade. EXTRACTIONS. Morgan’s universal extracting solution ( 8 ) ,
acetic acid (0.5 N ) , buffered a t pH 4.8 with sodium acetate. DETERMINATION OF NITRATE iiITROGEN. Brucine (Merck), 1% in concentrated sulfuric acid, is prepared just prior to using. The sulfuric acid should be free of nitrates. Nitrate nitrogen standard. Sodium nitrate, 0,0910 gram in lo00 ml. of extracting solution to supply 15 p.p.m. of nitrogen. DETERMINATION OF KITRITE NITROGEN. Dimethylaniline (Eastman 97), 10 ml., in 1 to 6 hydrochloric acid. Concentrated hydrochloric acid. Nitrite nitrogen standard. Potassium nitrite, 0.1210 gram in lo00 ml. of extracting solution t o supply 20 p.p.m. of nitrogen. DETERMINATION OF AMMONIUM NITROGEN. To make Graves reagent ( 5 ) ,80 grams of sodium chloride are dissolved in 130 ml. of water and 100 ml. of a cold saturated solution of mercuric chloride (7%) are added with shaking. The salt is almost dissolved and 70 ml. of a saturated solution of lithium carbonate (lye) are added in small quantities and with continued shaking. Five grams of talc are added to the solution, whichisfiltered. Stored in a brown bottle and kept stoppered, it will keep for several weeks, but needs t o be thoroughly shaken before use. Gum arabic, 0.25%; sodium hydroxide, 15%. Standard nitrogen. Ammonium chloride, 0.1521 gram in 1000 ml. of extracting solution to supply 40 p.p.m. of nitrogen. METHODS
PREPARATION OF SOILAND PLANT EXTRACTS. Detailed di-
rections for preparing extracts have been given (4).
I. Determination of Inorganic Nitrogen Fraction for Standard Nitrogen Fraction
Curves and in Soil and Plant Extracts Useful Volume of
Nitrate N
Material
Standard soln. Soil extract Plant extract
Range P.p.m. 0-2 0.6-12
Aliquots
M1.
Diluted to
M1. 15
0.6-12
0-2 2.5 2.6
Nitrite N
Standard soh. Soil extract Plant extract
0-5 2-10 2-10
0-5 10 10
20
Ammonium N
Standard soln. Soil extract Plant extract
0-5
0-25 5 5
20
4-80 4-80
DETERMINATION OF NUTRIENTS IN SOILAND PLANT EXTRACTS. Nitrate Nitrogen i n the Absence of Nitrite Nitrogen. Soil or plant extracts (2.5 ml.) are diluted t o 15 ml. with extracting solution and 7.5 ml. of brucine reagent are added cautiously down the side of tube. The contents are immediately stirred with a flat-bottomed’ rod. Photometer readings are taken after 15 minutes, using a 425 blue filter and adjusting the blank to 100. Nitrate Nitrogen i n the Presence of Nitrile Nitrogen. Nitrite nitrogen will produce color changes similar to those produced by nitrate nitrogen with the brucine reagent. A concentration of nitrite nitrogen is approximately 3 times as effective as one of nitrate nitrogen, and so 3 p.p.m. of nitrate nitrogen can be subtracted for every p.p.m. of nitrite nitrogen present in the extract (for photometer readings 100 t o 35). Nitrite nitrogen is determined by the method outlined blow. For more exact determination, standard amounts of nitrite nitrogen (0.1 to 1.0 p.p.m.) are treated with brucine as for the determination of nitrate nitrogen and a standard curve is drawn from the resultant data. The amount of nitrate nitrogen equivalent to the nitrite nitrogen present is calculated from the standard curves and deducted from the total amount. of nitrate nitrogen in the extract as shown by the brucine test. Nitn’te Nitrogen. Dimethylaniline solution (0.5 ml.) is added to each tube containing 10 ml. of soil or plant extract diluted to
July, 1944
A N A L Y T I C A L EDITION
44'1
20 ml. with extracting solution. The contents are stirred, 1 ml. of concentrated hyTable II. Recovery from Mixtures of Standard Solution and of Soil and Plant Extracts Plus drochloric acid is added, and contents are Standard Solutions stirred again. Readings are taken in 15 Nitrate Nitrogen Nitrite Xitrogen Ammonium Nitrogen minutes, using a 425 blue filter and adjustNitrogen Fraction Found Calcd. Diff. Found Calcd. Diff. Found Calcd. Diff. ing the blank to 100. P.p.m. P . p . m . P.p.m. P.p.m. P . p . m . P.p.m. P . p . m . P.p.m. P . p . m . Ammonium Nitrogen. Five milliliters 1\Iixed solution 3.6 4.0 -0.4 2.0 2 0 0 6.8 8.0 f0.8 of soil or plant extract are diluted to 20 ml. Plant extract 5.2 ... ... 0 ... . . . 4.8 . . . ... n~ithextractingsolutionand0.2ml.ofgum p'~~","d":",~$~~ 5,0 4,6 +o.4 1.4 l,o +o,4 5,6 j,4 +o,2 arabic solution is added. The contents soil extract 1.3 ... ... 1.0 ... ... 4 . 8 . . . ... arc mixed thoroughly by means of a flatS C ~ ~ 2~, ~ 2 ,; ; ~ ~ 1 .~6 ~ 1 . 5 +0.1 5.2 5.4 -0.2 bottomed rod, and 0.5 ml. of Graves' reagent is added. The contents are again mixed and 3.5 ml. of 15% sodium hydroxide are added to each tube, mixing immediately after the addition of the hydroxide. Readings are tents should again be mixed immediately after addition of the taken after 5 minutes, using a 425 blue filter and a null adjustGraves' reagent and mixed thoroughly after addition of sodium ment giving a reading of 100 with the blank. hydroxide. ACCURACY.The nitrate nitrogen determination can be reDISCUSSION OF METHODS peated within 0.1 p.p.m. for amounts of 0.1 to 2.0 p.p.m. of niA blank should be run on all determinations. It is convenient trate nitrogen. Nitrite nitrogen must be determined and deducto run about 12 samples at one time. Blocks to hold 13 vials tions made accordingly to evaluate properly the nitrate nitrogen (12 samples, 1 blank) facilitate handling. content, although the nitrite content of most plant and soil exThe use of 7.5 ml. of brucine reagent for 15 ml. of sample plus tracts can be ignored for practical purposes. The nitrite nitroextracting solution determines both nitrate and nitrite nitrogen. gen determination can be repeated within 0.2 p.p.m. for 1 to 5 If proportionately larger amounts of sulfuric acid were used, nip.p.m. of nitrogen. trates alone would be determined (3). However, higher concenThe ammonium nitrogen determination can be repeated within trations of sulfuric acid cause browning of organic constitu0.2p.p.m. for between 1to 5 p.p.m. of nitrogen. ents. The effects of nitrite nitrogen can also be eliminated by Where recommended aliquots are used, these variations reprethe use of sodium azide (1). It is simpler to use a low concentrasent 1.09 kg. (2.4 pounds) of nitrate nitrogen, 0.68 kg. (1.5 tion of acid and to compensate for the amount of nitrite nitrogen pounds) of nitrite nitrogen, and 3.63 kg. (8 pounds) of ammonium present. nitrogen per 908,000 kg. (2,000,000 pounds) of soil, and 24 p.p.m. For many soil and plant extracts the nitrite nitrogen content of nitrate nitrogen, 8 p.p.m. of nitrite nitrogen, and 32 p.p.m. of will be negligible. I n such cases, i t can be ignored, and the reammonium nitrogen in plant material on a fresh weight basis. sults obtained from the brucine test can be considered as indicaThe amounts determined in a soil and plant sample along with tive of the nitrate nitrogen content. the amounts recovered from samples and mixed solutions are The determination of nitrate nitrogen is influenced by the given in Table 11. In general, recoveries from mixed solutions concentration of acid present. If the acid is added directly to or from additions to soil or plant extracts are good. the diluted extract insufficient color is produced for the range of CONCLUSIONS nitrogen desired. Higher concentration of acid which would corRapid photometric methods for the determination of nitrate, rect this situation is unsatisfactory. If the brucine reagent is nitrite, and ammonium nitrogen in soil and plant extracts are added down the sides of the tube, it is possible to use sufficient given. Only one extraction of soil or plants is made, using one concentrations of acid without browning of the organic constituextracting solution for all determinations. Determinations are ents. The contents are mixed and thereby the relative cuncenmade on separate aliquots of the extract. tration of acid is reduced, so that the organic constituents do not Nitrate plus nitrite nitrogen is determined by brucine reagent, turn brown. It is important, therefore, to add the acid at a fairly nitrite nitrogen by dimethylaniline reagent. Kitrate nitrogen is uniform rate down the sides of the tube and to mix the contents obtained by difference (nitrate plus nitrite N - nitrite N = niimmediately with a flat-bottomed rod. trate N). Ammonium nitrogen is determined by means of I n the nitrite nitrogen determination the color is influenced by Graves' reagent. By careful attention to details, fairly accurate the concentration of hydrochloric acid used and by the amounts values can be obtained. of dimethylaniline. It is important t o measure these reagents carefully. LITERATURE CITED A small error is introduced in the nitrite nitrogen determina(1) Mellan, I., "Organic Reagents in Inorganic Analysis", p. 475, tion because of slight color t h a t is present in the extracts or apPhiladelphia, P. Blakiston's Son & Co., 1941. pears upon the addition of hydrochloric acid. The test is, there(2) Morgan, Y.F., Conn. AQT.E z p t . Sta. Bull. 450 (1941). fore, not accurate for less than 1p.p.m. of nitrite nitrogen in the (3) Snell, F. D., and Snell, C. T. "Colorimetric Methods of Analysis", Vol. 1, p. 635, New Ymk, D. Van Nostrand Co.,1941. soil or plant extract. It is best to ignore readings for less than (4) Wolf, B.,IND. ENG.CHEM.,ANAL ED.,15,248-51 (1943). this amount of nitrite nitrogen. (5) Yoe, J. H., "Photometric Chemical Analysis", Vol. 11, p. 98, I n the ammonium nitrogen determination, the precipitate New York, John Wiley & Sons, 1929. formed is influenced by the length of standing and by the gum arabic added. If allowed to stand much longer than 5 minutes the colloidal precipitate in some cases will settle out and make the readings inaccurate. Repeatable results can be obtained Authors, Attention! by taking readings exactly 5 minutes after addition of the soPossible delay in publication of articles and extra corredium hydroxide. spondence are the result of authors' failure to return manuThe use of 0.2 ml. of gum arabic aids in the suspension of the scripts with galley proof to the publication office of INDUSTRIAL colloidal precipitate and permits determination of larger amounts A N D ENGINEERING CHEMISTRY, Easton, Pa. Please, authors, of ammonium nitrogen. The Graves' reagent may settle out on make a point of attaching manuscript to proof and mailing Ptanding. If shaken to obtain a uniform suspension before using, both promptly in the envelope enclosed, as soon as you have it may be used for several weeks after preparation. had time to read the proof and note any necessary corrections The Graves' reagent should be added after the gum arabic has or changes. been thoroughly mixed with the contents of the tube. The con-
