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ANALYTICAL EDITIOhl
VOl. 3, KO.3
Method for Analysis of Volatile Compounds Containing Carbon, Hydrogen, and Nitrogen' W. Scholl and R. 0. E. Davis FERTILIZER AND FIXEDNITROGEN INVESTIGATIONS, BUREAUOF CHEMISTRY AND SOILS,WASHINGTON, D. C
N A study of t h e v a p o r A method of analysis for mixtures of gases containing jackets whose temperature is p r e s s u r e of the system ammonia, carbon dioxide, and water vapor has been controlled by c i r c u l a t i n g urea-water-ammoniadeveloped using solid absorbents whereby small samples water from a constant-temcarbon dioxide it became of a few milligrams may be analyzed accurately by p e r a t u r e bath. The total necessary, in order to determeasurement of volumes at reduced pressures. volume of the bulbs is such as mine the partial pressure of The method was also employed to determine nitroto permit expansion of the the constituents in the gas gen, hydrogen, and carbon in volatile organic materials gases to a pressure considerphase, to develop a method of whose products of combustion are composed of water ably less than the vapor presvapor, carbon dioxide, and nitrogen. analysis for small quantities sure of the material to be anaof gas containing carbon diThe method can be employed with accuracy where lyzed, to prevent condensasamples are too small to obtain accurate results by the tion on the walls of the bulbs. oxide, ammonia, and w a t e r vapor. Since the total velordinary method of determining the increase in weight Combustion of the gases is ume of gas available for analyof absorptive materials. carried out a t 550" C. on oxiA description of the apparatus is given and the dized copper gauze contained sis was often between 2 and 4 CC., it was found necessary method of procedure in analyzing gases and liquids is in the first quartz tube of unit to a d o p t a microanalytical outlined. G. Asecond quartz tube containing reduced copper gauze m e t h o d , after a number of tests had been tried using the ordinary absorption chain. is utilized to take up free oxygen and to reduce any oxides of The method finally adopted was based on the principle of nitrogen that might be formed in the first tube. Clear quartz the method described by Hackspill and d'Huart (a),but modi- tubes permitted inspection of the gauze to determine its fred t o suit the purpose of our investigation. While developed condition. The tubes are 350 mm. long and 13 mm. inside for use in analyzing a gas containing ammonia, carbon di- diameter. The gauzes in the first and second tubes are 120 oxide, and water vapor, it was also employed in test runs for and 90 mm. in length, respectively. Two independently the determination of the carbon, hydrogen, and nitrogen controlled electric furnaces are employed to heat the tubes. content of several volatile compounds containing these eleTwo glass bulbs, F and I , about 25 mm. in diameter, by ments. Since the beginning of this work somewhat similar alternate immersion in liquid air permit the passage of the methods of analysis for small quantities of gas have been gases back and forth through the heated tubes. This insures complete combustion of the gases. described by Prescott (4) and Ambler (1). Absorption of water vapor is accomplished by means of a Principle of Method U-tube, J , about 250 mm. long and 10 mm. inside diameter, The principle of the modified method is combustion of a containing a mixture of phosphorus pentoxide and pumice known volume of gas in the presence of copper oxide, and stone. the determination of the volumes of nitrogen, carbon dioxide, The bulb K , in conjunction with bulb I and similar to it, and water, of which the gas is composed after the combustion. is useful in drawing the gases back and forth through J The water was absorbed by phosphorus pentoxide and the in a manner similar to that explained above. combined volumes of carbon dioxide and nitrogen determined. By means of a Topler pump, L, the gases are transferred Then the carbon dioxide was absorbed by potassium hydroxide to tube N through a capillary tube, M , of 0.5-mm. bore. The and the volume of nitrogen remaining was measured. The lower end of the capillary is sealed into the bulb R and bent water was determined as the difference between the original upwards in the mercury. The volume of the pump is about volume of gas taken and the sum of the volumes of carbon 600 cc. and the ratio of its volume to that of the apparatus dioxide and ammonia (equivalent of the nitrogen volume). to be evacuated is about 3 to 1. Compressed air is used to The determination of water by absorption in phosphorus pen- lift the mercury from the lower bulb. The ground glass valve toxide differed from the method of Hackspill and d'Huart in Q acts as a check valve to prevent mercury from passing back that they separated the water by freezing it out a t -80" C., into the apparatus. and determined its amount from the volume of hydrogen The gases are collected for measurement in tube N whieh produced on allowing the water to react with calcium hy- is about 80 cm. long and of 8 mm. bore. Parallel to N and dride. The absorption of water by phosphorus pentoxide connected to it through a three-way stopcock, Ve, is a tube, was a simpler procedure and gave satisfactory results. 0, of the same dimensions. The two tubes are mounted in front of a calibrated white glass millimeter scale, and the whole Description of Apparatus unit surrounded by a water jacket through which is circulated The apparatus is shown in Figure 1. The functions of the water from the constant-temperature bath. The volume of tube N was determined carefully to within 0.01 cc. for each indicated units and their arrangement are as follows: The sample of gas for analysis is introduced at A and is 10-mm. length indicated on the scale. Tube 0 is used in conjunction with tube N to determine the pressure of the condensed in unit B at the temperature of liquid air. The condensate may be expanded to vapor in units C, gases collected in tube N . Both tubes are connected through D, and E. Unit D is an 80-cm. mercury manometer, and C Vs to a mercury leveling bulb. and E are calibrated bulbs with a total capacity of 600 and The U-tube P , containing lump potassium hydroxide, is 150 cc., respectively. The bulbs are surrounded by water used for absorption of carbon dioxide. The unit H is used for introducing samples of liquid mate1 Received March 16, 1931.
I
July 15, 1931
1NDUSTRIAL A N D ENGINEERING CHEMISTRY
rials in the study of the accuracy of the analytical method, liquids being more readily obtained in pure form and easily weighed in small capillaries in a manner similar to that described by Pregl (3), A ground glass cap closes one end, and this may be removed for introducing the sample in a sealed capillary. Stopcock V ~isZused to break the capillary tubes, and stopcock V11 prevents the entire apparatus from becoming filled with air when inserting the capillary. The entire apparatus with the exception of the two quartz tubes mentioned is made of Pyrex glass. The glass stopcocks are lubricated with a specially prepared grease made according to the directions given by Shepherd and Ledig (6). It is very necessary that this grease be of the proper consistency and exert no appreciable vapor pressure. The apparatus was connected to Hi-Vac and mercury vapor pumps, which were used to evacuate i t previous to each experiment. Experimental Procedure
I n making an analysis the entire apparatus is first completely evacuated, precaution being taken to heat the copper gauzes to 800" C. and to pass a small Bunsen flame over the kbing to drive out moisture and volatile gases, else the volume measurements will be too large. Units C, D,E, and the tubing to stopcock V z are filled with mercury; then with B immersed in liquid air, the gas to be analyzed is condensed in this unit. With stopcock Vz closed, the unit B is allowed to warm up to room temperature and then the gas is expanded into units C, D, and E, with the total pressure adjusted by means of the mercury leveling bulbs to between 50 and 60 mm. of mercury. Finally, immersing B in boiling water and filling the unit from B to stopcock V S with mercury completely transfers all the gas to C, D, and E. The pressure, temperature, and total volume are determined. A known volume of gas from E is transferred to bulb F by immersing the latter in liquid air. The gas is then completely oxidized by passing over the heated copper oxide several times, alternately immersing F and I in liquid air. While one bulb is immersed in liquid air, precaution should be taken to warm the other bulb and tubing with a small gas flame. After oxidation of the gas is complete, the stopcocks 176 and Vlo are closed and Va is opened, permitting the products of combustion, water, carbon dioxide, and nitrogen, to come in contact with the phosphorus pentoxide. By immersing bulbs K and I alternately in liquid air, the gas is drawn back and forth over the phorphorus pentoxide, insuring the absorption of all water. The residual gas containing carbon dioxide and nitrogen is now collected in N by operating the Topler pump until no appreciable quantity of gas is removed from the combustion part of the apparatus in a single operation of the pump. The volume of the nitrogen-carbon dioxide mixture in N is determined at a given temperature and reduced pressure. On opening V S ,the carbon dioxide is absorbed by holding the gas in contact with potassium hydroxide. The residual nitrogen is again collected in tube N by operating the mercury pump, and its volume, pressure, and temperature determined. From the volume of nitrogen measured, the equivalent volume of ammonia is computed. The difference between the total volume of gas sample and the sum of the volumes of ammonia plus carbon dioxide is a measure of the water present. All volumes are calculated to 0" C. and 760 mm. of mercury. In the analysis of liquid samples, the procedure is the same as with gas samples with the exception of a difference in the manner of introducing the sample to the apparatus. The liquid to be analyzed is filled into thin capillaries of known weight, about 1-mm. bore, and 20 mm. in length.
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After sealing, the capillaries are reweighed to determine the weight of sample introduced. With stopcock VII closed, a capillary cohtaining a known quantity of sample is introduced into unit H and supported in such a way that one end just enters the bore of the plug in stopcock Vlz. The end of the unit is closed by a ground glass cap and, after opening VI1, the apparatus, including the combustion and absorption units, is evacuated. Then stopcock VIZ is turned sufficiently to break the capillary and release the liquid, The vapors produced are oxidized and the analysis carried out, as already described, for the amount of water, carbon dioxide, and nitrogen. Results
A number of determinations using the method described were made of different materials, including liquids that readily vaporize or are gaseous at ordinary temperatures, and of the gas phase over a solid with considerable vapor pressure. The materials used were acetonitrile, CH,.CN, b. p. 81.5" C.; acetone, (CH&CO, b. p. 56.1" to 56.2" C.: ammonium bicarbonate, NHJIC03; and a mixture of ammonia and carbon dioxide. The results obtained are shown in Table I. I n the
Figure 1-Apparatus for Determination of Carbon, Hydrogen, a n d Nitrogen in Gaseous or Volatile Compounds
case of ammonium bicarbonate, the gas sample was taken from the gas phase in equilibrium with the solid at the temperature of 30" C. With the mixture of ammonia and carbon dioxide, the pressure was kept low enough (about 6 cm. a t 30" C.), in measuring the initial gas volume in unit E , not to. cause condensation of ammonium carbamate. The acetonitrile and acetone samples were specially purified by redistillation; the ammonium bicarbonate was freshly prepared from purified carbon dioxide and ammonia; and the carbon dioxide and ammonia were of known purity. e
Table I-Determinations MATERIALS Liquids Acetonitrile (CHaCN)
on Materials of Known Composition COMPONENT AMOUNT WEIGHT OF DETER- AMOUNTDETERSAMPLE MINED CALCD. MINED MR. 70 % N1 34:l 34:l 57.6 67.5 4.7 C H2 6.4 6.4
Acetone (CH8)zCO
8 3
Vapor in equilibrium with solid ammonium bicarbonate
15.2
Gas mixture Ammonia f carbon dioxide
7.4
C
62 0
61.5
NHa
21 5 55 7 22 S 53 5 46.5
21 7 55 3
coz
Ha0 NHa
cos
23 0
53 9 46.1
The method of calculation may be illustrated by employing the results obtained in the analysis of the gas in equilibrium
ANALYTICAL EDITlON
278
with solid ammonium bicarbonate. The volume of the sample of gas taken is measured at a given pressure and temperature. The combustion of the gas has the effect of producing one volume of nitrogen for two of the volumes of ammonia according to the equation 4NH3
Table I1 is a sample data sheet on the ammonium bicarbonate determination. Table 11-Test
+ 302 = 2Nz + 6H10
Hence the volume of nitrogen obtained represents twice that volume of ammonia in the original sample. The volume of carbon dioxide is not changed during combustion, whereas the original volume of water is increased by the water derived from the oxidation of ammonia. This increased water volume is of no consequence in the analysis, however, since all the water is absorbed by phosphorus pentoxide before measuring the carbon dioxide and nitrogen. The volume of water in the original sample is determined as the difference between the volume of the original sample and the sum of the volumes of carbon dioxide measured directly, and of ammonia calculated from the measured nitrogen. All volumes are reduced to 0” C. and 760 mm. of mercury by use of the gas law equation 273 pv 760(t 273) where p = pressure of gas in mm. of mercury v = volume in ml. t = temperature in O C. =
+
22400
Vapor sample
on Ammonium Bicarbonate Vapor in Equilibrium with Solid Ammonium Bicarbonate AMOUNT PRESDETERVOL. SURE TEMP. VOLa WEIGHT MINED Ml. Mm. C. MI. Mg. % 66.34 63 29.9 4 32 15.2
Analysis:
Nz $.
6.14 4 71
COz
Nz
295 5 130.3
30 6 30.7
Experimental results: NHs = (2 X 0.73) COz = (2.15-0.73) f4.32 (1.42f 1.46)l HzO Total
-
Calcd. values: NHs
1.46 1.42 1 3 4.32
3.3 8.4 3.5 15 2
21.7 55.3 23.0
21.5 55.7 22.8
coz
HzO a
2.15 0.73
At 0’ C. and 760 mm. pressure.
Although the method described has been employed on volatile or gaseous compounds whose products of combustion consist of water, carbon dioxide, and nitrogen, it was developed for the analysis of a gas composed of ammonia, carbon dioxide, and water vapor in determining the partial pressures of these constituents. Literature Cited
The weights in grams of the gases were calculated from the volumes V Oby the equation V OX mol. wt. of gas W =
Yol. 3, KO.3
(1) Ambler, H R ,Analyst, 64,517 (1929). (2) Hackspill, I,.,and d’Huart, 0 , Ann. ckzm , [lo]6, 96-107 (1926). (3) Pregl, F.,“Quantitative Organic Microanalysis,” pp 62-65, Blakiston, 1924. (4) Prescott, C H , Jr , J . A m Chem SOL,60,3237-40 (1928). (5) Shepherd, M., and Ledig, P. G , IND. ENC.CHEM, 19,1059 (1927).
Determination of Sodium in Organic Compounds Use of Uranyl Acetate Method’ D. L. Tabern and E. F. Shelberg ABBOTTLABORATORIES, NORTH CHICAGO, ILL.
URING the Course of
A modified uranyl acetate method has been applied from the barbiturate soluto the analysis not only of alkali barbiturates, but also tion by acidification and exan extensive study of traction, sulfated ash deterthe salts of c e r t a i n of other typical organic sodium salts. Results thus obtained substantiated by other studies, minations u p o n the filtrate newly synthesized barbituparticularly in the field of electrometric titrations, lead yield the e x p e c t e d values. rates (8), the commonly acto the conclusion that the commonly accepted sodium The r e a s o n f o r t h e intercepted sodium sulfate (sulsulfate method is not applicable to the analysis of f e r e n c e of the organic porf a t e d a s h ) m e t h o d was tion of the molecule in t h e f o u n d t o yield v e r y uncertain alkali barbiturates. s a t i s f a c t o r y r e s u l t s in above instances is not clear. the case of sodium ethyl-(1-methylbutyl) barbituric acid Such a modified sodium sulfate method is too cumbersome (Nembutal). Not only did the results vary from determina- for general use and distinctly inferior to several methods to be tion to determination. but average values were sometimes described. as much as 1 per cent below theexpected. Variation: in Methods Employed the technic of analysis, as well as in the mode of synthesis Efforts were first directed toward the establishment of the of the salt, failed to bring improvement. Investigation demonstrated that a t least two other analo- purity of the various samples of Nembutal a t hand. Both gous salts, sodium ethyl-sec-butyl- and sodium ethylisoamyl- loss on drying in vacuo a t 120’ C. and extractable barbituric barbituric acid (sodium Amytal), behaved in somewhat the acid were found to be negligible. Nitrogen determined by same way. This was doubly surprising in view of the fact the Kjeldahl method checked theory closely (found, 11.27 that the sodium sulfate method has long been employed for and 11.16; calculated, 11.3). Determination of the barbithe analysis of sodium barbital, sodium Neonal, (sodium turic acid content by decomposition of the salt with dilute ethyl-n-butyl-barbituric acid), etc., and had just been made sulfuric acid and extraction yielded very close to the calcuthe official method for the analysis of sodium Amytal, one lated amount. Further confirmatory evidence was supplied by p H deof the compounds in question (4). After the conclusion of most of the work described subse- terminations. Five per cent solutions of several lots of quently, it was found that if all organic matter is removed carefully purified Nembutal gave values ranging from 9.6 to 9.75, as did a synthetic solution made from ethyl-(11 Received March 16,1931.
D
