affect the solubility of the nitroguanidine as it does when present with methylene chloride. The results given in Table I1 show that a 4-hour extraction of a nitroguanidine-type powder (Cordite N) with the azeotrope completely removes the nitroglycerin and stabilizer. After evaporation of the azeotrope, followed by solution of the residue in acetic acid, average values of 8.84% nitroglycerin and 1.94% centralite were obtained as compared with 8.85 and 2.027& respectively, after direct extraction d h 65% acetic acid. The lowboiling (35.5’ C.) azeotrope is more easily and quickly removed from the extracted material in the flask than a high-boiling solvent such as carbon tetrachloride (76.5’ C.), in which the solubility of nitroguanidine is also negligible. Possible secondary reactions, particularly with diphenylamine-stabilized powders, have been known to occur a t the high extraction temperatures (1). The low boiling point of the azeotrope ensures that such reactions taking place in the powder will not be unreasonably accelerated. This point becomes important in the examination of powder extracts by
Table II. Determination of Nitroglycerin and Centralite in Cordite N Powder by Extraction with 65% Acetic Acid and Pentane-Methylene Chloride Azeotrope
Replica 1
2 3 4 5
(4-hour extraction of 1-gram sample with both solvents) Nitroglycerin, yc Centralite, yo ~65% acetic Pentane65y0acetic Pentaneacid CHgC12 acid CH2Clz 8 86 8.85 1.99 1.99 8.81 8.85 2.03 1.93 8.86 1.99 8.86 1.93 8.84 2.06 8.82 1.93 8.88 2.03 8.84 1.93 8.84 .4v. 8.85 1.91 2.02
chromatographic and spectrophotometric methods. During extraction with apparatus, a steam bath may be employed as the heat source rather than a n electrically heated unit. This eliminates obvious hazards, should the solvent be evaporated to dryness. LITERATURE CITED
(1) California Institute of Technology, National Defense Research Committee, Office of Scientific Research and Development, Progress Report on “Chromatographic Studies of
Smokeless PoTders and Related Subst,ances,” OSRD 1837 (Sept. 25, *_”“\ lY*S).
(2) Horsley, L. H., associates, Advances in Chem. Series, No. 6 , 23 (1952). (3) E. S. Naval Ordnance Test Station, “Comparison of Solvents Regarding Solubility of Nitroguanidine,” 6th Meeting JANAF Analvtical Chemistry Pgnel, Oct. 8-9, c953.
RECEIVED for review September 14, 1956.
Accepted November 13. 1956. The opinions or assertions contained in this article are the private ones of the writers and are not to be construed as official or reflecting the views of the Navy Department,
Vacuum Fusion Determination of Oxygen and Nitrogen in Lanthanum D. T. PETERSON and D. J. BEERNTSEN lnstifufe for Atomic Research and Departmenf o f Chemistry, lowa State College, Arnes, lowa
,Because of the effect of impurities on the rare earth metals, a reliable analytical method for the determination of oxygen, nitrogen, and hydrogen i s essentiai. The vacuum fusion technique was modified to permit analysis of lanthanum metal. The lanthanum sample was dropped into a nickel bath and heated to 1900’ C. The average recovery of added oxygen was 90.9%, with a probable error of 1.7%. The loss of approximately 9% of this added oxygen was probably due to adsorption by the vaporized nickel. The analysis was completed by a mass spectrometric determination of the composition of the evolved gas.
and modern, economical methods of separation, the rare earth metals have ITH IXCREASED AVAILABILITY
254
ANALYTICAL CHEMISTRY
received increased attention in research. These metals are reactive and their properties can be significantly changed by small quantities of oxygen, nitrogen, and hydrogen. The latter two of these can be determined by existing analytical methods, but no satisfactory method has yet been advanced for the determination of oxygen in the rare earth metals. I n a conventional vacuum fusion analysis, the sample to be analyzed is heated in a graphite crucible, either alone or in a metal bath. A bath is used to decrease the volatility of the sample metal as in the analysis of manganese and high-manganese steels and to aid the reaction of carbon mith oxides and nitrides in the sample, as in the analysis of titanium metal. Under such conditions, oxides are reduced and carbon monoxide is evolved, while nitrides and hydrides are decomposed and nitrogen and hydrogen are evolved.
The gases are collected, measured, and analyzed. Because of its inconvenience in the vacuum fusion procedure, a bath is used only when necessary, as in cases in which the metals are very volatile. The vapor pressure of pure lanthanum metal a t high temperatures is low (1) and that of lanthanum carbide is probably still lon-er. However, fusion of lanthanum in a graphite crucible at temperatures up to 2000” C. did not yield a quantitative recovery of oxygen or nitrogen. Gettering of evolved gas probably was not the cause, as very little metal vaporized t o the walls of the furnace tube. The possibility of using iron. which is the classical bath material for vacuum fusion, was investigated. Evolution of carbon monoxide and nitrogen was incomplete a t temperatures up to 1850” C. A consideration of the properties of nickel indicated that it might be a satis-
factory bath material. Using nickel as a bath for lanthanum samples, it was possible t o obtain good results for nitrogen and oxygen. Though no standard hydrogen samples were analyzed, it seems safe to assume its complete evolution. APPARATUS
The vacuum apparatus was composed of a furnace section and an analytical section. Furnace Section. The furnace was of the Guldner-Beach type (2) and was entirely air-cooled. It consisted of a 90-mm. borosilicate glass cylinder with a ground-glass seal a t the bottom. A 6 4 mm. Vycor crucible was supported in the cap that closes this cylinder. An Acheson graphite heating crucible and a funnel were supported in the Vycor carucible by Acheson graphite powder. The heating crucible was 3/4 inch in inside diameter, 16/le inches in outside diameter, and 3'/z inches long, and was equipped with a magnetically operated cover. The graphite crucible was heated inductively by a 6-km. Ajax high frequency converter. The induction coil rvas 4 inches in diameter and 5l/, inches tall and consisted of 37 turns of flattened copper tubing. The loading tree, used for storage of samples and bath material, and the optical window were above the furnace tube proper. The window was protected from metal vapor by a. magnetically operated shutter a t all times except when a temperature reading was being made. Analytical Section. Gases from the furnace section were pumped into the analytical section by a three-stage mercury diffusion pump, Model 15-01, made by Consolidated Vacuum Corp. Since the gases were analyzed mass sy:ectrometrically, the analytical unit \\-as simple. It consisted essentially of two known volumes and an accurately calibrated McLeod gage. At the top of the RlcLeod gage capillary tube was a three-way high-vacuum stopcock with a standard-taper joint for the attachment of gas sample bulbs for mass spectrometric analysis. An oil diffusion pump evacuated the gas bulbs through the third stopcock position and also eracuated the remainder of the analytical section. The mercury for the 1IcLeod gage and the cutoffs was raised by atmosplieric pressure and lowered by means of a small auxilixry meckanical pump. A11 swls in the furnace and analytical sections n-ere made n-ith Apieeon Ti- high vacuum sealing ax. The three-way st,opco,,k on the AlcLeod gage \vas 1ubricBated iyith Don-Corning high vacuum grease. G A S ANALYSIS
The collection system and McLeod gage were capable of collecting up t o 4 X mole of gas. The amount of gas could be measured to a precision of about 0.3% a t 1 X l o w 4mole and mole. When about 1.6% at 6 X a gas sample had been collected and its
pressure measured, part of it was forced into the evacuated sample bulb, using the McLeod gage as a Toepler pump. The relative proportions of the gases present were determined with a mass spectrometer. Carbon monoxide, nitrogen, and hydrogen were the only gases evolved in significant quantities from the lanthanum-nickel bath. Since carbon monoxide and nitrogen both give their major contribution to the 28 mass peak, these two were measured by the ratio of the 29 to 28 mass peaks. The 29 mass peak is due to carbon-13 plus oxygen-16 and nitrogen-15 plus nitrogen-14. The carbon-I2 to -13 and nitrogen-15 to -14 isctope ratios are very well known. The sensitivity of the isotope ratio method \!as estimated on the basis of analysis of synthetic gas samples prepared from pure carbon monoxide and pure nitrogen to be & l volume %, which is n-ell within the requirements of vacuum fusion practice. PREPARATION OF OXYGEN STANDARDS
I n order to check the accuracy of the method, samples containing known amounts of oxygen were prepared by adding gaseous oxygen to lanthanum a t 500" C. The lanthanum had been prepared by calcium reduction of lanthanum fluoride and was subsequently melted in magnesium oxide a t 1050' C. under vacuum. Pieces of this metal were melted a t 1200" C. under vacuum in calcium fluoride crucibles for 30 minutes to form cylinders approximately 3/4 inch in height and 518 inch in diameter. All samples for oxygen addition and blank analysis were pie-shaped slices cut from these cylinders with a jeweler's saw. Each sample to which oxygen was added was filed clean, neighed, and sealed, under argon, in a 50-ml. bulb, which had a high vacuum stopcock a t one end and a 6-inch-long, l/zinchdiameter extension a t the other end. The bulb was evacuated and filled with oxygen to a measured pressure. The sample was moved to the end of the extension and the extension vias then inserted into a furnace a t 500" C. From the volume of the bulb, the oxygen pressure. and the weight of the sample, the weight per cent oxygen was calculated, assuming that all of the oxygen had reacted n ith the sample. Upon heating, the metal surface immediately turned blue from oxide formation. Soon after, white threads of oxide began to appear on the surface of the metal, apparently forming on nuclei of pre-existing oxide particles. After a few hours the oxygen pressure had become negligible. When the heating time was extended to 16 to 24 hours, the oxide threads coalesced nith the mass of the metal and although they nere still visible, the danger of their being lost in handling was reduced considerably. Also, with extended heating,
the surface of the metal lost its gunmetal blue appearance and regained much of its silvery metallic luster. ANALYTICAL PROCEDURE
Preparation of Sample and Bath. A representative sample was cut from the lanthanum stock metal with a jeweler's saw and was given a preliminary smoothing with a file. The bath consisted of about 50 grams of nickel, which was sufficient to permit a t least six 1-gram samples to be analyzed before changing the bath. The nickel used in these experiments vas cut from a 3/4-inch-diameter bar of greater than 99% purity, and was cleaned in warm hydrochloric acid and then washed with distilled water and acetone. The cleaned nickel, the lanthanum samples, and a loading tree were transferred to a glove box, which was evacuated and then filled rrith argon. The lanthanum samples were filed clean, neiglied, and placed in the arms of the loading tree. When lanthanum standards were to be analyzed, they were transferred in their preparation bulbs to the glove box. The lanthanum metal was protected from the atmosphere at all times, particularly after having been cleaned in the glove box. The glove box was used when handling lanthanum in order to reduce the amount of reaction of the lanthanum with atmospheric gases. The nickel was also plated in the loading tree, which was then transferred to the argon-filled vacuum fusion apparatus, \There it was sealed in position with Apiezon W wax. Preparation of Apparatus. JYhen the loading tree had been placed in position, the system was evacuated slorvly, so t h a t tile graphite powder insulation was not ejected from the Vycor container. After the diffusion pumps had begun operating, heating of the crucible was initiated. The temperature was raised slowly, as the gases liberated by heating also tend to eject the graphite powder insulation. The temperature was raised to 2300" to 2400" C. and held for about 3 hours to degas the furnace. After 3 hours at 2400" C.:the pressure in the furnace section usually had fallen to about 5 x 10-5 mm. as measured with a cold cathode gage. The crucible temperature was lowered to 1300" to 1400" C. and the nickel for the bath was dropped into the crucihle. Then the temperature was brought slowly up to 1900" C. One t o 1.5 hours a t 1900" was usually sufficient t o attain a steady blank rate, which was of the order of 0.05 to 0.08 ml. per hour (S.T.P.) or 2.2 X l o p 6 3.6 X mole per hour. When it had been ascertained that the blank rate at 1900" C. had reached a steady value, a blank determination was made over the time-temperature cycle to be used in the lanthanum analysis. To aioid undue splashing and spitting from rapid hydrogen and nitrogen evolution, the temperature was lowered to 1300" to 1400" C. before dropping the lanthanum samples into the nickel bath. The temperature was then raised VOL. 2 9 , NO. 2, FEBRUARY 1957
0
255
to 1900" C. in about 4 minutes and held there for about 11 minutes. Analysis of Sample. After the blank determination had been completed, the power was shut off for 6 minutes t o gjve a crucible temperature of 1300' to 1400' C. The cutoff to the oil diffusion pump was closed and, if the amount of gas expected was small, the cutoff to the extra volume was also closed. A sample was dropped into the crucible, the cover closed, and heating begun a t maximum power. After 4 minutes the temperature had reached 1900" C. and the converter control was set to maintain this temperature. Most of the gas was given off in the first 5 minutes, but it was collected for 15 minutes to ensure maximum recovery. It was possible to run samples a t 30minute intervals. RESULTS
A N D DISCUSSION
Using the procedure outlined above it has been possible to recover as carbon monoxide an average of 90.9% of the oxygen added to lanthanum samples. The probable error of this average of 11 analyses was 1.7% (see Table I). As the oxygen content of the base metal was not known, the method could be evaluated only by addition of a known amount of oxygen and observing the amount which was recovered. The assumption was made that the same amount of gas would be evolved from a given weight of the lanthanum base metal when the standard samples were analyzed as when the base metal was analyzed. Evaluation of any method
Table
Sample Wt., G. 1.02 1.34
1.
Analysis of Lanthanum with Added Oxygen
Oxygen Added,
wt. y* 0.133 0.218 0.193 0.183 0.224 0.139 0.206 0.153 0.318 0.366 0.208
0.75
0.96 1.05 1.36 0.93
0.88
0.61 0.36 0.95
for oxygen analysis of lanthanum metal must make this assumption, unless lanthanum metal known to be free of oxygen was available for the preparation of standard samples. The oxygen recoveries were calculated by subtracting the amount of gas evolved by an equivalent weight of the base metal from the total amount of gas evolved by the standard sample and comparing the amount of oxygen recovered as carbon monoxide with the amount of oxygen added to the standard sample. The analytical results on the lanthanum base metal are given in Table 11. The base metal contained an amount of oxygen which nas small compared to the oxygen additions. The most probable explanations for the loss of 9% of the added oxygen are the mechanical loss of part of the oxide coating on the standard samples, the adsorption of part of the evolved carbon monoxide by the nickel which is evaporated from the crucible, and the incomplete evolution of carbon monoxide from the bath. The last explanation does not seem likely, as very rapid evolution of the carbon monoxide, followed by a return to a low blank rate, w-as observed in every analysis. The carry-over of gas within the bath could account for the high results which were occasionally obtained. However, there did not seem to be a consistent sequence of a low result followed by a high result using the same bath. The samples to which more oxygen was
Oxygen
Recovered, Wt. 0 130 0.188 0.195 0.153 0.205 0.124 0.171 0.147 0.260 0.380 0.178
Average
Table II.
1LO4
86 90.9
Analysis of Lanthanum Metal Used to Prepare Standard Samples and Typical Lanthanum Metal
Lanthanum Sample St.ock
Typical No. 1 Typical No. 2
256
5
Recovery 98 86 101 84 92 89 83 96 82
ANALYTICAL CHEMISTRY
0.0391 0.0398 0.0389 0.0612 0.0746 0.0482 0.0521
Nitrogen, Wt. yo 0.0136 0.0169 0.0140 0.0290 0.0334
Hydrogen, n7t.yc
0.0745
0.00063 0.00074
0.0732
0.00003
0.000003
added and from which lanthanum oxide loss should be more likely did not show a lower recovery of oxygen. Considerable amounts of nickel were evaporated from the crucible and formed a mirror plate on the upper walls of the furnace tube. The adsorption of the evolved gases by this nickel surface was probably responsible for the failure to achieve complete recovery of the oxygen. This was confirmed by the results of analyses of samples of Armco iron, using an iron bath and a nickel bath. The results of these analyses, given in Table JII, show a recovery of 94% when a nickel bath is used. The results given in Tables I and I11 indicate that the recovery, although less than loo%, was constant and reproducible. If the oxygen analyses are corrected for this incomplete recovery, the results should be accurate. The analysis of lanthanum-oxygen standards in a nickel bath was attempted a t temperatures below 1900' C. It was not possible to achieve consistent or accurate results a t temperatures below 1825' C. Khen analyses were attempted a t lower temperatures and the temperature was subsequently raised to 1800' C. or above, increased gas evolution was observed and particles could be seen being ejected from the crucible. I n work with titanium, other workers (3, 4)believed that oxygen was retained within titanium carbide cinders a t high temperatures. It seems possible that this also happens with lanthanum in a nickel bath below 1800' C., with the carbide cinder dissolving in the melt, releasing the trapped oxygen a t higher temperatures. A temperature of 1850' to 1900' C. as necessary for the analysis, even though temperatures in this range increased the amount of vaporized metal collected on the ~ a l l s of the furnace. The determination of nitrogen in lanthanum by vacuum fusion appears to be simple and accurate. The use of an iron bath did not give accurate results for nitrogen, but by using the nickel bath a t 1600" C., complete recovery of the nitrogen was achieved, as indicated by the agreement between vacuum fusion and Kjeldahl analyses
Table 111.
Analysis of Armco Iron
Total Gas Evolved, Calculated as Xt. yc Oxygen
Iron bath 0 0385 0 0391 0 0385 0 0384 0 0391 0 0398 Av. 0 0389
Nickel bath 0 0361 0 0372
0 0366
Table IV.
Sample 1 2
Analysis of Lanthanum for Nitrogen
Vacuum Fusion, Wt. 0 104 0 105 0 093 0 0114 0 0119 0.0119
Kjeldahl, wt. 70 0 1002 0,0998 ..
.. ..
..
(Table IT). Only three comparisons were made because of the greater interest in the more difficult oxygen determination. I n the operating procedure the samples are dropped into the bath at 1300" C. and the bath is then heated to 1900" C. As the nitrogen appeared to be liberated completely a t
1600" C., most of the nitrogen should be pumped out of the furnace well below 1900" C. and the temperatures a t which volatilization of nickel becomes troublesome. Since precision and accuracy were obtained at 1600" C., the procedure as developed for evolving the oxygen should be satisfactory for nitrogen. No standard samples containing knoii n amounts of hydrogen n ere analyzed. Hydrogen seemed to be rapidly and completely evolred from either an iron or a nickel bath a t 1600" C. As the hydrogen is easily eyolved and should not be adsorbed to a greater extent than carbon monoxide, the standard oxygen procedure should give accurate results for hydrogen. ACKNOWLEDGMENT
The authors would like to thank F. H.
Spedding of the Ames Laboratory for supplying the lanthanum metal used in the study. They would like also to acknowledge the work of H. J. Svec and J. E. Capellen in developing the isotope ratio method of gas analysis and for performing the analyses. LITERATURE CITED
(1) Daane,
H., "T'apor Pressure of 1,anthanum and Praseodymium," U S. -4tornic Energv Commission,
AECD-3209 ( A u ~ 1, . 1991). (2) Guldner, IT. G., Beach, A . L., ,4SAL. CHEM.22, 366 (1950). ( 3 ) Kroll, IT. J., Schlecton, A . IT., Truns. Electrochem. SOC.93, 247-58 (1948). (4) Kalter, D. I., ANAL CHEM.22, 297303 (1950).
RECEIVED for reviex May 10, 1956. Accepted Kovember 19, 1956. Contribution N o . 488. JTork performed in the rimes Laboratory of the U. S. Atomic Energy Commission.
Paper Chromatographic Detection of Galacturonic and Glucuronic Acids MILDRED
GEE
and R. M. McCREADY
Western Utilization Research Branch, Agriculfural Research Service, United States Department of Agriculfure, Albany 1 0, Calif.
,A procedure for the tentative identification of galacturonic acid on paper chromatograms in the presence of glucuronic acid is described. The mixture containing glucuronic acid is partially lactonized and chromatographed. Characteristic migration rates, the hydroxamic acid-ferric ion test for lactones, and the specific lead acetate test for galacturonic acid served to identify these substances,
9 with sodium hydroxide, and then it produces a single spot. The present report describes a procedure whereby a combination of the basic lead acetate test (3, 4) and the reaction of hydroxamic acid with ferric ion used for lactones and esters ( I ) served to identify galacturonic and glucuronic acids by paper chromatography. EXPERIMENTAL
P
CHROhlATOGRAPHY is used widely for the tentative identification of the sugars produced b y the hydrolysis of polysaccharides. Most sugar mixtures are resolved with the proper irrigating solvent, or if resolution is poor they are selectively detected by a particular indicator. Mixtures of glucuronic and galacturonic acids are difficult to separate by irrigating with the usual chromatographic solvents, although a mixture of pyridine, ethyl acetate, acetic acid, and water (6) can be used to separate these substances. Solutions of glucuronic acid usually contain glucuronolactone and produce double spots on a chromatogram (6). Glucuronolactone can be hydrolyzed to sodium glucuronate by titration to p H APER
Paper Chromatography. Aqueous solutions of t h e uronic acids were applied t o Whatman No. 1 filter paper sheets with micropipets and the sheets were then dried in air at room temperature. The papers were irrigated in the ascending direction (2) with a solvent of ethyl acetate, pyridine, mater, and acetic acid in a ratio of 5:5:3:1 (6) and dried in air without heating until they were free from acetic acid. Appropriate color reagents were then applied as described below.. Fivemicroliter amounts of solution to be tested produced spots of 10-mm. diameter upon application on Whatman KO. 1 paper. After irrigation, the spots had diffused t o a diameter of 15 mm. Uronic Acids. Five-microliter amounts of lY0 uronic acid solutions were applied t o paper sheets and the sheets were dried, irrigated, and tested with the following results.
Glucuronic acid lactonized by heating a 1% solution a t p H 2 and 80" C. for 30 minutes gave double spots when chromatographed. Glucuronic acid titrated to p H 9 with sodium hydroxide gave a single spot. Galacturonic acid apparently does not lactonize under these conditions and gal-e but a single spot when chromatographed. Color Reagents. TKOgrams each of aniline and crvstalline trichloro-. acetic acid hydrate were dissolved in 100 ml. of ethyl acetate. T h e dried chromatograms t o be tested were dipped in this solution and permitted t o dry in air for 15 minutes. T h e dried paper sheets were then heated for 5 minutes a t 95' C. T a n spots on a white background appeared in t h e presence of 10 y or more of reducing uronic acids. A saturated, aqueous solution of basic lead acetate was prepared and filtered. The dried paper chromatograms to be tested for galacturonic acid were dipped rapidly through the aqueous lead acetate solution, blotted to remove excess solution, and heated for about 1 minute in a cwrrent of live steam. -4 brick-red spot on a n-hite background was produced with 25 y or more of galacturonic acid. Hvdroxamic Acid-Ferric Ion Test for Lactones ( I ) . The solution of alkaline hydroxylamine should be prepared fresh before use. Seven grams VOL. 29, NO. 2 FEBRUARY 1957
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