concentrations within the limits that are suggested in the procedure. To obtain accurate results in the analysis of a 0-1-gram sample of NBS 126a, sufficient nickel was added to the blank so that its nickel concentration was. 338 p.p.m. Ions which were found to interfere with this determination fall into three classes; ions which precipitate in the strongly alkaline media; ions which are highly colored; and ions which form stronger complexes than biuret with the Cu, Co, and Ni ions. The ions which precipitate in the strongly basic media include Fe+2, Fe+3, Pb+Z, Mg-2, Cd+2, M n f 2 , Bg+*, and Bi+a. Highly colored ions such as the permanganate ion interfere. When NH4@is present in concentrations greater than 1000 p.p.m. the formation of ammonia complexes interferes. The presence of tartrate ion can be tolerated in quantities up to
500 p.p.m. Higher concentrations lead to the formation of a mixed copperbiuret tartrate complex. No interference was found for Na+, K+, ea+*, ZnfaJ Ti+8,SIf*, and Al+a when present in concentrations up to 1000 p.p,m. The interference due to iron was eliminated by extracting the iron as FeCla with diethyl ether. The sensitivities of the four metal ions are Go, 0,197 p.p,m.; Cr, 0.0056 p.p.m.; Cu, 1.25 p.p.m.; and Ni, 0.655 p.p.m. These are taken as the concentration of each ion needed to produce a change in absorbance of 0.005. LITERATURE CITED
(1) Ayres, G. H., Baird, S. S., Talanta 7,237 (1961). (2)Brunch, O.,2. angew. Chem. 20, 834 (1909). (3) Chilton, J. M., ANAL.CHEY.25, 1274 (1953).
te rmi nation
(4) Kato, M., 27. anoag u. allgem. Chem.
300.84 (1959’1. (6)-&to, ’ M., ‘Komuro, Y., Sone, K., J. Chem. SOC.Japan, Pure Chem. Sect. 75,1134(1954). (6) Ibid. 77,308 (1956). (71,Lundell, G., Hoffman, J., Bright, H., Chemical Analysis of Iron and Steel,” p. 41,Wiley, New York, J931. (8) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 3rd ed., Vol. 111,p. 398,Interscience, New York, 1959. (9) Schwartzenbach
G., “Complexometric Titrations,’” p. 78, Interscience, New York, 1957. (10) Yoe, J. H., Jacobs, W. D., Anal.
Chim. Acta 20,332(1959). (11) Ibid., 20, 435 (1959). (12)Youness, Tawfig A. H., M. S. thesis, The Ohio State University, 1955. RECEIVEDfor review August 4, 1961. Accepted October 13, 1961. Taken in part from a theais presented to the Graduate School of the Ohio State University by Vaughn K. Gustin in partial
fulfillment of the requirements for the degree of master of science,December 1960.
m nd Potassium rotates
RENATO SELLER1 and ORE§TE CALDlNl Research Department, Societb Italo-Britannica 6. Manetti, H. Roberts & Co., Florence, Italy Orotic acid yields soluble salts with monium and substituted ammonium bases. The resulting solutions precipitate N a + and K+ as the slightly soluble sodium and potassium orotates. Those reactions can be adapted to the gravimetric determination of sodium and potassium in the absence of each other. Unlike any other gravimetric method, potassium can be determined the presence of ammonium ions. any other cations do not interfere. N a recent patent (11) we described salts obtained by the interaction of orotic acid and 2-dimethylaminoethanol (DMAE) or 2-diethylaminoethanol (DEAE). Our interest in that occasion was based chiefly on the high solubility in water of the two salts, in the light of the therapeutic applications of orotic acid. We realized, however, by the time of our expcriments, that orotic acid was of interest from the analytical standpoint as well, inasmuch as its sodium and potassium salts are slightly soluble in water and in strongly polar solvents, and are of a definite composition. Therefore, we decided to ascertain whether alkanolammonium orotates could be of use in the gravimetric determination of sodium and potas-
sium.
A5 for sodium, the reagents recorded in the literature which precipitate this cation are few. Besides the classical method using double uranyl acetates which precipitate the corresponding triple salts with sodium, the determination of sodium as the resorcinolate ( I ) , as the salt of y-methyldicyanodihydroxyhydropyridine (Q), as the 5alt of 3,6-dinitro-2,5-dihydroxy-p-benzoquinone (nitranilic acid) (8), and as the bi-D,bmethoxyphenyl acetate have been described (IO). More recently, Dranitskaya (6) and Berenshtein and Freger (3) described the precipitation of K a + with the magnesium salt of l-naphthylamino-$-sulfonic acid and made this method the basis of a gravimetric determination of sodium. I n the case of potassium, a substantial number of reagents are known that detect and determine this cation b y gravimetric procedures. Apart from those that have already earned their place in textbooks-as, for instance, chloroplatinic acid, perchloric acid, sodium cobaltinitrite, dipicrylamine, and tetraphenylboron-other gravimetric determinations of potassium are recorded as the 6 - chloro - 5 - nitrotoluene 6sulfonate (4) as the &nitrobarbiturate (diliturate) (6),as the 12-phosphomolybdate (B), and as the fluoborate (7). Toei (19-16) preoipitated potassium with derivatives of dipicrylarnine , tetra-
-
nitrophenothiaeine, tetranitroacridone and 2,4-dinitronaphthosultam. However, as far as our present knowledge goes, there is no organic or inorganic reagent that precipitates potassium in the presence of ammonium ions except the ethanolammonium orotates. We preferred to use DMAE or DEAE orotate as the precipitant instead of ammonium orotate because precipitation is effected by the use of an excess of the reagent alcoholic solution. The alkanolammonium salts which result from ionic displacement are, as a rule, more soluble in alcohol than the corresponding ammonium salts and do not interfere with the composition of the precipitates. EXPERIMENTAL
Reagents. N,N-Dimethyletha?olammonium Orotate. I n a 1-liter flask, 78 grams (0.5 mole) of orotic acid are suspended under reflux with 500 ml. of methanol. Fifty grams (about 0.55 mole) of freshly redistilled 2-dimethvlaminoethanol are added slowly. %en the reaction misture is almost clear, heating ifi discontinued and a little decolorizing charcoal is added. The solution is filtered while still hot. On cooling, N,N-dimealiylethanoI~monium orotate crystallizes in prisms. The crystals are collected, washed with methanol, and dried in the air; m.p.
142-4' C. Upon recrystallization from methanol, the pure product is obtained, map. 149' @. (11). N,N Dimethylethanolammonium Orotate, 0.1M. Dissolve 24.53 grams of recrystallized N,N-dimethylethanolammonium orotate in about 800 ml. of lukewarm methanol, cool, and make t o 1liter. N,N-Diethylethanolammonium Orotate. The procedure is similar to that for the dimethyl homolog. The reagent quantities are as follows: 78 grams (0.5 mole) of orotic acid, 400 ml. of ethanol, and 64 grams (about 0.55 mole) of freshly redistilled 2-diethylaminoethanol . The crude product melts at 128-9' C. When recrystallized from ethanol the melting point is raised to 132' C. (11). N,N-Diethylethanolammonium Orotate 0.1M. Dissolve 27.33 grams of recrystallized N,N-diethylethanolammonium orotate in about 800 ml. of lukewarm ethanol, cool, and make to 1 liter. Either of the above reagent solutions may be used for the precipitation of Na + and K +. Procedure. The solution under test (or the unknown) should contain about 1 meq. of sodium or potassium in 4 t o 6 ml. of water and be between pH 6.5 and 8.0. An excess of reagent solution (20 t o 25 ml.) is added dropwise while the reaction vessel is gently swirled. The precipitation mixture is allowed to stand in a refrigerator (3"C.) for 2 hours, then the precipitate is collected with suction on a tared Gooch (or fritted-disk) crucible and washed twice with 2-ml. portions of 70% methanol (or ethanol, according to reagent solution used) and twice more with 2-ml. portions of 95% ethanol. The crucible is dried to constant weight in an air oven a t 105' C.and weighed.
-
Conversion factors for calculations are reported in Table I. A number of analytical reagent grade salts of sodium and potassium have been examined to check the accuracy and reproducibility of results. These are summarized in Table 11. Owing to the relative solubility of sodium and potassium orotates in water, precipitation is complete only in the presence of a substantial excess of alcoholic reagent solution. Moreover, washing the precipitates with alcoholic solutions which are too weak may result in appreciable loss of weight. The influence of washings is depicted in Table 111. PROPERTIES
Sodium Orotate, CsHsNtOJTa.
Mol. wt., 178.087; white crystalline powder, slightly soluble in water
(0.00294 gram per ml. at 25" CJ, insoluble in methanol and ethanol.
Table 1.
Conversion Factors
Analysis. Calcd.: 6,33.74; H, 1,70; N, 15.74; Na, 12.91. Found: C, 33.9 H, 1.83; N, 15.83; Na, 13.03.
Weighed Sought Na orotate Na Potassium Orotate, CeHaN204K, NaeO NaCI same structure as t h e Ma salt. Mol. wt., 194.19; white crystalline K orotate K powder, slightly soluble in water K20 KC1 (0.00257 gram per ml. at 25' insoluble in methanol and ethanol;
e.),
Table 11.
Salt Used NaCl Na2CzOc NaZHPO,, 12Hn0 NazSaOs. 5H20 KC1
&so4
KNOZ KNaC,ELOs. 4 6 0 aNa+K.
Accuracy
Factor 0.12913 0.17406 0.32823 0.20135 0.24252 0.38390
and Reproducibility of Results % of Na or K
Wt, Wt. of Ne or K Taken, Orotate, Mg. Mg. Calcd. Found
in Salt Used Calcd. Found
Error
65.32 75.26 198.90 143.41 76.37 90.00
39.34 34.32 12.84 18.53 52.44 44.87
$0.38' -0.32 +0.80 f1.07 -0.71 +0.46
199.0 200.0 200.0 205.8 198.9 200.6
106.00 203.7 151.62 200.W
Analysis. Calcd.: C, 30.94; H, 1.56; N, 14.43; K, 20.13. Found: C, 30.88; H, 1.57; N , 14.38; K, 20.32. Sodium and potassium have been determined in their orotates as the sulfated ash. DISCUSSION
The sensitivity of the reactions involved in this method allows for the detection of 1 part Ma+ in 20.000 parts of water at 3' C., and 1 part K + in 16.000 parts of water a t 3' C., provided that the solution under tests is treated with twice its volume of either reagent solution. When operating in aqueous medium, neither lithium, the alkaline earth metals, ferric iron, aluminum, nickel, cobalt, or copper interferes with the precipitation of sodium and potassium. Lack of interference from ammonium may be of special significance for determination of potassium where volatilization of ammonium salts can lead to losses by decrepitation. LITERATURE CITED
(1) Barreto, A., Rev. chim. ind. (Rio G% Janeiro) 5, 416 (1936). (2) Belcher, R., Robinson, J. W., Anal. Chim. Acta 8,239 (1953). (3) Berenshtein, A. V., Freger, S. V., Pochvovedenie 1957, No. 2, 126-7. (4) Davies. H.. Davies, W.. J . Chem. SOC. 1923, 2976. '
( 5 ) Dranitskaya, R. M., Trudy Odessk. Univ., Sbornik Khim. Fakul'teta, 3, 89 (1953); Referat. Zhur. Khim., Abstract No. 5779 (1955).
199.8 199.4 201.6 208.0 197.5 201.5
39.49 34.21 12.94 18.73 52.07 45.08
202.8 38.67 38.52 202.20 22.00" 22.24a
Log of Factor
+
10 9.11103 9.24071 9.51618 9.30395 9.86475 9.58422
Mean % of Error
% of
1
-0.39) fl.10..
f0.43
(Na)
-0.10 IK) ,--I
... .. ..
Table 111. Influence of Washings 10 ml. aqueous 0.1M solution of NaCl or KCl 20 ml. ethanol. 0.1M solution of DEAE orotate (3" C.) NaCl Found, Mg. KC1 Found, Mg. (calcd. 58.4) (calcd. 74.5)
+
Washing Washing Washing Washing A B A B 52.9 53.9 55.8 54.1 56.0 53.8
57.8 58.6 59.0 58.3 57.4 59.1
72.1 71.5 70.8 72.6 71.7 73.0
74.8 73.6 74.6 75.1 73.8 74.1
Washing A, four times, with 3-ml. portions of 70% ethanol. Washing B, twice with 2-mi. portions of 70% ethanol and twice more with Zml. portions of 95% ethanol.
(6) Fredholm, H., 2.anal. chem. 104, 400 (19361. ., . \ _ _ _
(7) Manasevit, H. M., ANAL. CHEM.27, 81 (1955). (8) Marensi, A. D., Villalonga, F., Anales farm. y bioqulm. (Buenos Aires) 11, 105 (1940). (9) Piccinini, G., Rend. soc. chim. ital. (Rome) 6 (1907). (10) Reeve, W., Christoffel, I., ANAL, CHEM.29,102 (1957). (11) Selleri, Renato, Caldini, Oreste (to L. Manetti, H. Roberts & Co., Soo. Italo-Britannica), Belg. Pat. 584,467 (May 9, 1960). (12) Toei, K., J . Chem. SOC.Japan 76, 106 (1955). (13) Toei, K., Nippon Kagaku Zasshi 76. 1083 (1955). (14) b i d . , 76, 1085 (1955). (15) Ibid,, 77, 670 (1956). (16) Ibid., 77, 1270 (1956).
RECEIVEDfor review August 7, 1961. Accepted October 17, 1961. VOL 33, NO. 13, DECEMBER 1961
* 1945
