Rapid Interferometric Analysis of Germane-Hydrogen Mixtures M I S 0 GREEN, Lincoln Laboratory. Massachusetts Institute of Technology, Cambridge, Mass., AND F \ L L €1. ROBINSON, Lincoln Laboratory, Massachusetts Institute of Technology, Cambridge, 'Mass., and Department of Chemistry, Polytechnic Institute of Brooklyn, Brooklyn, N . Y . Rayleigh-Zeiss interferometer, fitted with a 500-mm. double-chamber gas cell, has been used for assaying germanehydrogen mixtures. The method depends upon measuring the difference in refractive index between hydrogen and the germanehydrogen mixture, and so involves an initial calibration with germanehydrogen mixtures of known composition. This method of analysis was used for determining the amount of germane (germanium hydride, GeHd) in the hydrogen evolved a t the cathode during the electrolysis of solutions of various germanium compounds. I n the Rayleigh-Zeiss interferometer light from a narrow slit is rendered parallel by a lens, split into two beams by a double slit, passed through two identical tubes containing the gases to be compared, and then through two identical glass plates. The emergent beams are recombined to form interference fringes. Where the gases in the two tubes differ in refractive index, the band system is displayed sideways. This displacement can be compensated by changing the inclination of one of the glass plates which is attached t o a micrometer screw with a measuring drum. The point for exact compensation is found by comparing this first band system with a second system formed by two beams which have traveled identical paths. The construction and operation of the interferometer have been fully described ( 1 , 2). The only innovation was the thermal insulation of the main body of the instrument to prevent it from being affected by rapid room-temperature fluctuations. The light Source used \Tag a tungsten filament lamp. r THE
1
The gss-handling apparatus is shown schematically in Figure 1. The dotted lines enclose t h a t part of the apparatus used for making up known germane-hydrogen mixtures. The germane used v a s purified by trap-to-trap distillation under high vacuum until its vapor pressure a t two different temperatures corresponded to Paneth's values (3). A compressed supplv of
electrolytic hydrogen (assayed 09.87, H, 4 ith water as major impurity) was used, and was dried by passing it through anhydrous calcium sulfate, barium oxide, and two traps immersed in liquid nitrogen. The difference in refractive index between dried hydrogen and spectroscopically pure hydrogen was measured and found t o be negligible-i.e., a few divisions on the measuring drum of the micrometer screw. CALIBRATION OF INTERFEROMETER
The procedure used for obtaining mixtures of known conlposition was as follows: With mercury completely filling the graduated limb, A , all the lines were evacuated, and stopcock B was closed. The required amount of germane was admitted into A and the three-way stopcock, C', was then closed; the mercury levels in the U-tube mere lowered by drawing mercury into reservoir D; limb E was evacuated, and the volume and pressure of germane in A were measured. The difference between the mercury levels in the limbs of the U-tube was a direct measure of the pressure in A , and was measured using a cathetometer. Hydrogen was admitted to A and, with stopcock C closed, the new pressure and volume were measured. With the pressure and volume data obtained, the composition of the mixture could be calculated. The mixture was pipetted into the interferometer chamber, F , by raising the mercury level in A until the pressure of gas was a little in excess of atmospheric pressure; stopcock G was closed and the gas lines were evacuated. The interferometer chamber, J , was filled with hydrogen to a pressure slightly greater than 1 atmosphere. Each interferometer chamber was opened t o the atmosphere through an 80-em. length of I-mm. bore capillary tubing, which effectively prevented the diffusion of air into the chambers when stopcocks IC and L were opened. The pressure of gas in the chambers fell to atmospheric pressure, The number of divisions on the measuring drum of the micrometer screw, which corresponded to a null-point reading for the mixture, was read. The temperature and pressure xere noted and the null-point value corrected to 0" C. and 76 cm. of mercury. Fifteen different mixtures varying from 0.64 to 12 58 mole 70 germane were used to obtain a calibration curve. The slope of the calibration curve, which was assumed to be linear, was obtained using the method of least squares, applying the restriction that the error6 I arise from uncertainty in the composition of the I mixtures and not from the interferometer readI I ings. It was found that 100 divisions = 0.506% I germane (the null-point reading with both I I chambers evacuated was 30 divisions, and this I must be subtracted from the number of divifH* sions read before using the above equivalent). I I
I I
I I I I I
I I
I I
I I
I I
I I I I
ANALYTICAL PROCEDURE
The dried gaseous mixture was collected over mercury in pipet X . One end of the pipet was attached to the interferometer chamber and the other end to a mercury reservoir, as shown in Figure 1. The air trapped in the mercury line a t .V was bled out through tube R. Stopcocks P and S were opened and the mixture v a s pipetted into the evacuated chamber until the pressure of gas was a little over 1 atmosphere. Chamber J was filled with hydrogen and the refractive indm difference measured, as described.
I
I I
I I
Figure 1.
The germane content of the mixture was calculated using the relation:
V
Gas-Handling Apparatus
1913
=
0.141 X d X TIP
ANALYTICAL CHEMISTRY
1914 where mole percentage of GeHl in H? null-point reading, divisions, after subtracting the zero reading 2’ = temperature, degrees Kelvin P = barometric pressure, mm. of mercury
T7 d
= =
The accuracy of this method, with the germane-hydrogen mixture made up as described and the 500-mm, is
*0.05’ % germanel and the range is to 15% germane’ The main advantage of this method is the rapidity with which analyses can be performed, about 10 minutes per determination,
an important matter when a large number of samples have to be analyzed. LITERATURE CITED
(1) Adams, L. H., J . Wash. A c a d . Sci., 5, 265 (1915). ( 2 ) Candler, C., “Modern Interferometers,” London, Hilger and watts, 1951. (3) Paneth, F. .1.,and Rabinonitsch, E., Ber., 58B, 1138 (1924). RECEIVED for review June 4. 1953. Accepted .kuguSt 10. 1953. Research supported jointly b y Army. S a r y , and Air Force under contract with hlassacliusetts Inbtitute of Technology. Work done as part of a thesis submitted by Paul H. Robinson in partial fulfillment of the requirements for the degree of ma-ter of >ripnce.
Mass Spectrometric Analyses of Some Six- and Seven-Carbon Alcohols V. -4. YARBOROUGII Carbide and Carbon Chemicals Co., Division of Union Carbide and Carbon Corp., South Charleston, K’. Va. ECEST
advances in the design of commercial mass spectrom-
R eters---e.g., close temperature control of the source, suppression of metastable ions, fabrication of metal inlet systems that eliminate the use of stopcock lubricant, and accurate measurement of pressure in the 0- to 100-micron range (12)-permit the examination and analysis of compounds that, heretofore, could not be studied. The last-mentioned improvement, particularly, has widened the scope of masc spectrometers considerably. Previously, more cumbersome micromanometers ( 1 4 ) or calibrated micropipets ( 3 ) were required, which often were not entirely dependable for mixtures with vapor pressures less than 50 microns.
test that method, its accuracy, and its reproducibility, three mixtures containing knom-n amounts of 3-heptanol, 2-heptanolj 4-heptanol, P-eth>-l-l-butanol, and 1-hexanol were analyzed. These results are summarized in Table I. The reproducibility is within +5% of the value of the contained component. The average deviation of a given component from its known value (for all three mixtures) is 8.2%. The maximum single deviation is 19.3% of its known value. The mass patterns for these five alcohols are presented in Table 11.
APPARATUS AND PROCEDURE
A Consolidated mass spectrometer Model 21-101, convei ted to Nodel 21-103, was used for all analyses. The samples were introduced into the instrument through a mercury orifice (21, which was modified in these laboratories by &I. L. RlcTeer and G. E. Mellen to the design presented in Figure 1. A capillary micropipet (S),pictured in Figure 2, was used to introduce the samples through this mercury orifice into the preleak bulb. When a sample was to be introduced, the Teflon plug was removed, and the container holding the liquid to be analyzed was inserted in the orifice. The Teflon plug was broken away from the vacuum seal by the disk threaded to the shaft of thp plug. The pressure of the mercury above forced the liquid out of the pipet into the inlet system of the spectrometer. The size of the micropipet (about 0.0005 ml.) was such that, upon complete expulsion and expansion of the liquid into the 3-liter, preleak bulb, the desired pressure (about 30 microns) was attained. From two viewpoints this system had a decided advantage over the older technique which employed a sinteredglass disk under a mercury seal (10): The time of introduction was shortened considerably; and difficulties due to adsorption in the sintered glass and loss from fractionation, both of which are characteristic of the sintered glass disk, c ere greatly minimized. The sample passed directly from the orifice to the 3liter, preleak bulb, in which the pressure m-as measured r ~ i t ha micromanometer ( I d ) . Compounds containing a hydroxyl group tend to be adsorbed on the walls of the inlet system through hydrogen bonding. For samples containing alcohols, therefore, the system had to be saturated several times with the mixture in question. This was accomplished by introducing the sample into the mass spectrometer, leaving it there for 2 minutes, and then pumping the sample out again. Usually, after several such “saturation” treatments, the mixture could be reproducibly analyzed. A “pump-out” period of 10 minutes between runs is adequate.
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1
TT‘8”
WAX JOIN-
1
8n
RESULTS
The analyses of mixtures of oxygenated compounds-e.g., alcohols, ketones, aldehydes, etc.-have been reported ( 4 4 , 9, 11, 13). The present paper describes a method developed for the analysis of mixtures of six- and seven-carbon alcohols. To
Figure 1. Diagram of Mercury-Covered Orifice
