April 15, 1942
*
313
ANALYTICAL EDITION
of nitrite nitrogen, including those between 0.015 and 0.001 p. p. m. Such a finding would eliminate once and for all the effect of water dilution even in those cases where small amounts of nitrite nitrogen mere to be found. One of the very early developments of the investigation disclosed the necessity of thorough mixing after the addition of each chemical to obtain reliable and consistent results. The ammonium sulfamate was nest eliminated, since it had no practical value other than destruction of the excess nitrite in the diazotization reaction, an excess which does not exist in the detection of nitrites in mater. The problem of obtaining equivalent color intensity for equivalent amounts of nitrite nitrogen, by adding reagents to the nitrite in the more concentrated condition as prescribed by Shinn, or in the more dilute condition for use nith water, appeared to have a bearing on the pH of the unknown nitrite volume. The acid concentrations, pH, and time for color development were investigated. It was found that equivalent color intensities for equivalent amounts of nitrite nitrogen could be developed by using 2 ml. of 1 to 1 hydrochloric acid in the reaction instead of the prescribed 1 ml. Because of the fairly large total volume of reagents required sonie consolidation of the reagents and their volumes was deemed advisable. This was accomplished by using 2 ml. of a 0.5 per cent sulfanilamide solution in 1 to 1 hydrochloric acid, instead of 5 ml. of a 0.2 per cent water solution of sulfanilamide and 1 nil. of 1 to 1 hydrochloric acid. The acid solution had the additional advantage of aiding in the dispersion of the sulfanilamide. K h e n stored in a refrigerato], there is little danger that the sulfanilamide will crystallize out. By using this modified reagent, the time required for full development of color was found to be 15 minutes, and the color intensity was not only equivalent as developed in both dilute and concentrated volumes for like quantities of nitrite nitrogen, but mas of sufficient magnitude in the range of even 0.015 to 0,001 p. p. m. of nitrite nitrogen to give differentiations which were as easily detected 3s those in the standard method (1). An advantage of the Shinn method over the btandard rnetliod is that the inaximum color developed in 13 minutes is more rapid and more stable. I n the Shinn method the nitrite value of the sulfanilamide standard is determined from a nitrite standard in which assayed sodium nitrite is used instead of silver nitrite. Throughout all the investigational work on the use of the t n o new reagents, sulfanilamide and X-(1-naphthyl)-ethylenediamine dihydrochloride, comparisons were made with Sessler tubes containing nitiite standards prepared from assayed sodium nitrite rather than a sulfanilaniide standard which is used in a pliotoelectric colorimeter and whose nitrite value is determined from a nitrite standard prepared from assayed sodium nitrite. Xaterworks people are familiar nitli the old nitrite standard and from a xiterworks practice standpoint it would be out of place to discontinue its use a t this time. The simplicity of the preparation of the nitrite standard from the desiccated reagent grade of sodium nitrite should not be overlooked. This lias been tlioroughly investigated in the laboratory of the Indianapolis Kater Company, and found to be reliable and accurate, eliniinating the long and laborious procedure using silver nitrite ( 4 ) . Table I shon s the comparison with the pi e m i t standard method and gives the quantities required by the Shinn method to obtain good color differentiation. Readings as high as 0.0002 nig. of nitrite nitrogen in 50-ml. Sessler tubes can e:tsily be differentiated in increments of 0.00004 mg. of nitrite nitrogen in 50 ml. and readings as high as 0.0005 mg. of nitrite nitrogen in 50 ml. can easily be differentiated in increments of 0.00005 mg. of nitrite-nitrogen in 50 ml. It is suggested that sodium nitrite solutions of two concentrations I)e used in making up the standards.
TABLE I. PREPARATION OF STANDARD KITRITESOLCTIONS (Quantities for 50-ml. Nessler tubes) Nitrite Solution of S h i m Method.
A. p, H, A , Standard Method tritea Solution of 1 MI. = 0.0005 M g . of XO2-N Standard nitrite soln. MI. 0.1
0.00005
0.2
0.00010
0.4
0.00020
0.7
0.00035
1 .o
0.0005
1.4
1.7
2.0 2.5
XOz-S M g.
0.0007 0.00085
0.001 0,00125
rh~:$‘2:;‘ 2
a~&~~~$a~!‘~ NOrN Standard nitrite soln. XOPN M1. Mq. 2.0 0.00004 4.0 6.0 8.0
0.00008
3.0 3.5 4.0 4.5 5.0
0.0006 0.oooi 0,0008 0.0009 0.0010
0.00012 0.00016 10.0 0.00020 1 to 1000.0.1 per cent 1 MI. = Approximately 0.0002 Mg. of -NO.-N _.. 0.00025 1.25 1.5 0.00030 0.00035 1.75 2.0 0.0004 2.5 0,0005
0 Listed as prescribed in ( I ) , although closer increments are probably possible.
-Modifications The 50- or 100-ml. unknowns are compared with a series of standards in matched Nessler tubes instead of against a single standard in a photoelectric or Duboscq colorimeter. Xitrite standards are prepared from assayed sodium nitrite instead of a sulfanilamide standard whose value has been determined from assayed sodium nitrite. Ammonium sulfamate is eliminated as reagent. The solution is thoroughly mised after the addition of each chemical, whether unknown or standard. Two milliliters of 0.5 per cent sulfanilamide in 1 to 1 hydrochloric acid are used, instead of 5 ml. of 0.2 per cent sulfanilamide and 1 ml of 1 to 1 hydrochloric acid to increase the sensitivity from 0.015 to 0.001 p. p. m. of nitrite nitrogen, thereby making the sensitivity range comparable to the present standard method range.
Conclusions The method as published is not applicable to waterworks practice, because of lack of sensitivity in the range from 0.015 to 0.001 p. p. m. of nitrite nitrogen. The present limitation of the water sample to 35 ml. or less is awkward and contrary to waterworks practice. The method can be made applicable by certain modifications.
LiteraLure Cited (1) Am. P u b . Health Assoc., “Standard Methods of Water Analysis”, 8th ed., pp. 10, 46 (1936).
(2) Assoc. Official Agr. Chern., Official and Tentative Methods of Analysis, 4th ed., pp. 216, 505 (1935). (3) Bratton, A. C., and Marshall, E. K., Jr., ,J. Bid. Chem.. 128, 537 (1939). (4) Rejndollar, \Ti. F., IKD. ENG.CHEM., Ax.41,. ED., 12, 325 (1940). (5) Shinn, SI. B., Ibid., 13, 33 (1941).
COILRECTIOS. In the article on ‘‘AYSLLJ’ of Benzaldehyde” [IsD. ESG.CHEM.,ANAL.ED.,14, 154 (1912)] the reference cited in the 35th line, second column, following the rvords “bromophenol blue”, should be (6).
JAXET G. DISKELSPIEL
