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solution completely, even with excess phosphoric acid, and consequently the color change of the indicator was obscured. An investigation to ascertain the minimum concentration of ferric alum that could be used showed that 100 ml. of a 5% solution was sufficient. Two other indicators-i.e., barium diphenylamine sulfonate (0.3 ml. of a 0.2% solution) and tri( 1,lO-phenanthro1ine)iron(II1) sulfate (1 drop of the B. D . H. reagent)-could be used in place of the indicator stated earlier. The proposed procedure is simple, rapid, and accurate and serves for routine analysis as well as an occasional assay. Reoxidation of the reduced titanium is avoided by keeping the end of the reductor immersed in the collecting liquid, and the negligible blank value obtained shows that this procedure results in no diffusion of ferric ions from the alum solution to the reductor. This technique offers advantages over methods in which the reduced titanium is titrated directly. The method is useful
in cases where a high calcium content in the titaniferrous material precludes the use of the Powell method. The method can also be applied to samples with low titanium content (See colorimetric values in Table 11.). Chromium as Cr04-z does not interfere. Vanadium is reduced in the Jones reductor, liberating Fe(I1) from ferric alum (1) and interferes if present in appreciable quantities. With the silver reductor, however, this problem does not arise if ferroin is used as the indicator for the titration with dichromate. With appreciable quantities of vanadium, therefore, the values for TiOz will be higher by the amount of vanadium present. A correction is thus necessary after estimating the vanadium by a separate method. ACKNOWLEDGMENT
The authors thank L. J. D . Fernando of the Geological Survey Department for providing the necessary facilities for this work and with whose permission this paper is published.
LITERATURE CITED
Hillebrand, W. F., Lundell, G. F., Bright, H. A,, Hoffman, J. F., “Applied Inorganic Analysis,” 2nd ed., Wiley, Sew York, 1953. ( 2 ) Malmstadt, H. T., Roberts, C. V., , ANAL.CHEM. 28, 1412 (1956). ( 3 ) Page, J. O., Gainer, A. B., Zbad., 31, (1)
1399 (1959). ( 4 ) Powell, A. R., Schoeller, W. R., Analyst 55, 605 (1930). ( 5 ) Rahm, J. A., ANAL. CHEM.24, 1832 (1932). ( 6 ) Schoeller, W. R., Powell, A. R., “Analysis of Mjyerals and Ores of the Rare Elements, 3rd ed., Hafner, New York, 1955. ( 7 ) Shapiro, L., Brannock, W. W., U . S . Geological Sursey Bull. 1036-C, p. 32 (1956). (8) Shippy, B. A , , ANAL.CHEM.21, 698 (1949). ( 9 ) Thompson, J. M., Ibid., 24, 1632 (1952). (10) Thornton, W. M. Jr., “Titanium,” p. 98, ACS Series, New York, 1927. (11) Vogel, A. I., “Textbook of Quantita-
tive Inorganic Analysis,” 2nd ed., Wiley, New York, 1951. J. P. R. FONSEKA Geological Survey Department N. R. DE SILVA Columbo, Ceylon
Gas Chromatographic Analysis of Hydrogen-Helium Gas Mixtures SIR: The use of zeolites for the gas chromatographic separation of light inorganic gases has been reported by many investigators ( I , 2, 4, 5 ) . Most separations required long adsorption columns, cryoscopic temperatures, and
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(00
90
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80
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unique sampling systems. Recently, a method for separation of helium, neon, and hydrogen was reported using molecular sieve and argon carrier gas (3). For routine control analysis of hydrogen-helium gas cylinder mixtures in our laboratory, a rapid method is employed at ambient temperatures using a 12-foot column containing Molecular Sieve 5X. No previous treatment of the Molecular Sieve, such as temperature activation, is necessary. A gas t sampling valve provides a simple and direct method for injecting known, reproducible volumes of sample into the gas chromatograph. Kitrogen gas is employed as a carrier. Complete separation is obtained in 7 minutes.
RESULTS
The relative response factors for hydrogen and helium are obtained by sampling equal volumes of both gases and integrating their respective areas with a planimeter. Excellent resolu-
90
i.
t
EXPERIMENTAL
Figure 1. Chromatogram of hydrogen-helium gas mixtures Solid line: H?, 60% and He, 40% Broken line: HB, 8C% and He, 20% Sample, 0.25 cc.; ottenuation, 8
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ANALYTICAL CHEMISTRY
Apparatus. A Perkin-Elmer Model 154D thermal conductivity gas chromatograph equipped with a gas sampling valve is used with a Leeds and Northrup I- t o 5-mv. recorder. T h e column is a 12-foot aluminum, ‘/4inch 0.d. tube, packed with 18-50 mesh Molecular Sieve 5A (Linde Co.). T h e column and detector temperatures arc both ambient, approximately 25” C. Since the sample components have thermal conductivities higher than that of the carrier, the detector is set a t 8 volts reverie polarity. Volumes of 0.25 cc. are sampled directly from the cylinders using the PerkinElmer gas saml~lingvalve. The nitrogen carrier outlet flow rate is 12 cc. per minute.
Figure 2. Chromatogram of hydrogen-helium gas mixture; Hz, 97% and He, 3% Sample, 0.25 cc.;
attenuation H e ( I ) , H2 (16)
tion and retxoducibilitv are obtained. Figure 1 is the typicrd chromatogram of a 60 hydrogen: 40 helium commercial gas mixture and hydrogen: 2o helium gas mixture. This method has been employed for the determination of helium as low as 3% in hydrogen as observed in Figure 2
LITERATURE CITED
(1) Brenner, N., Coates, V. J., Nature 181, 1401-2 (1958). ( 2 ) Janak, J., Krejci, M., Dubsky, H. E., Chem, ~ i52 (6). ~ 1099-1107 t ~ (1958).
( 3 ) Krejci, k., Tesarik, K., Colleciion Czech. Chem. Commun. 25 (3), 691-4 (1960).
(4)Kyryacos, G., Boord, C. E., ANAL. CHEM.29. 787 11957). ( 5 ) Lard, E: W., 'Horn; R. C., Ibid., 32, 878 (1960). ELLIOT H. BAUM
Materials Laboratory Sperry Gyroscope Co. Division of Sperry Rand Corp. Great Neck, N . Y.
Note on a Reversed Oxyacetylene Flame SIR: The June 1963 issue of ANACHEMISTRY 17ontains a paper by Hans F. Loken, James S. Teal, and Eugene Eisenberg (p. 875) describing a modified Beckman flame photometer burner employed for the flame spectrometric determination of calcium. The modification consists essentially of causing the fuel, acetylene, to flow through the central or oxyger tube of the burner
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LYTICAL
while the oxygen surrounds the burning fuel. This arrangement was used by the writer some years ago, albeit not with a Beckman burner, and referred to as the "oxygen sheath" in U. S.Patent 2,858,729, Kovember 4, 1958, specification and claims. The advantages of the arrangement received comment in the patent specification. Further development and improvements along with the
filing of additional patent applications have been in progress and now the perfected burner forms part of the flame spectrophotometers manufactured and marketed by the Keyes Scientific Corporation, 122 Hampshire Street, Cambridge, Mass. FREDERICK G. KEYES Physical Chemistry Laboratory Massachusetts Institute of Technology Cambridge, Mass.
Determination of Ammonium, Amide, Amino, and Nitrate Nitrogen in1 Plant Extracts by a Modified Kieldahl Method SIR: Studies of nitrogen metabolism in the authors' laboratory required separation and recovery for isotopic analysis of the various nitrogen fractions present in green leaiTes after the addition of either Kr\'150:ror (S15H4)2S04 to the leaves. Quantitative recovery of ammonium and nitrate nitrogen was necessary to prevent contamination of amino and amide nitrogen with unmetabolized tracer. A method for the determination of ammonium, amide, nitrite, and nitrate nitrogen has been described by Varner et al. ( 4 ) . However, two limitations were encountered while trying to apply their method in this laboratory: nitrate reduction was incomplete and amin, nitrogen was not estimated. The modified melhod described in this communication permits the determination of ammonium, amide, amino, and nitrate nitrogen with minimal contamination of amide and amino nitrogen by unmetabolized tracer nitrogen. EXPERlMliNTAL
Apparatus. Semimicro - Kjeldahl Distillation Unit. Reagents. Borate Buffer. Saturated solution of sodium tetraborate adjusted t o p H 10 with X a O H . Mercuric Sulfate Solution. Ten grams of red HgO dissolved in 100 ml. of 4h' H2S04. Sodium Hgdroxidcb-Sodium Thiosul-
fate Solution. Na2S203 (42 grams) dissolved in 1 liter of 14-V NaOH. Boric Acid-Mixed Indicator Solution. Ten grams of boric acid and 5 ml. of mixed indicator of methyl red (2 volumes of solution of 200 mp. of indicator in 100 ml. of water) and methylene blue (1 volume of solution of 100 mg. of indicator in 50 ml. of water) made to 500 ml. with distilled water. Potassium Biiodate Standard Solution. KH(IO& (3.897 grams) dissolved in distilled water and diluted to 1 liter. Procedure. T h e following procedure gives a n accurate estimate of t h e amounts of ammonium, amide, amino, and nitrate nitrogen present in a plant extract. Ammonium Nitrogen. X portion of a 70y0 ethanol extract of plant tissue is transferred to a 100-ml. semimicro-Kjeldahl flask and evaporated to dryness a t room temperature utilizing a jet of air. T h e flask is placed in a water bath a t 90" C . and attached t o the distillation unit. A small amount of silicone antifoam agent is added to help prevent foaming. Twenty-five milliliters of water and 5 ml. of borate buffer are added through the distillation head after attaching the 125-m1. receiving flask, containing 15 ml. of the boric acid-indicator qolution. A vacuum is created in the system using a water pump, and distillation is conducted for 30 minutes. Amide Sitrogen. The receiving flask containing the boric acid-indicator solution is replaced, and 5 ml. of 40% potassium hydroxide solution and 25 ml.
of water are added through the distillation head. The vacuum distillation is continued for 30 minutes at 90" C. Sitrate Nitrogen. The receiver is changed again, and a large piece of mossy zinc and 25 ml. of water are added to the Kjeldahl flask. The nitrate reduction process requires 4 hours a t 90" C. for complete reduction of 2 mg. of nitrate nitrogen. Distillation of the ammonia may be accomplished during or after reduction. However, a large volume of water will be collected in the receiver if the vacuum distillation is conducted during the entire 4-hour reduction period. Amino Nitrogen. The distillation head is rinsed into the Kjeldahl flask, and the mossy zinc is rinsed and removed b y forceps from the flask. After adding 10 ml. of concentrated sulfuric acid and 0.5 ml. of the mercuric sulfate catalyst, the flask is placed on an electrically heated digestion rack. The water is boiled away slowly before applying full heat for digestion. Upon completion of the digestion, 14,V sodium hydroxide is added to the flask under a cold water tap until most of the sulfuric acid is neutralized as indicated by cessation of the violent reaction and the allpearance of precipitated ?;a2SO4. The flask is attached t o the distillation unit, and the solution is made basic with excess sodium hydroxide-sodium thiosulfate solution. A vacuum distillation is conducted for 15 minutes a t 90" C., collecting the ammonia in boric acid-indicator solution. The ammonia collected in each of the VOL. 36, NO. 2, FEBRUARY 1964
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