METHYL VACCENATE, M.W.296 CH3 (CH&CH = CH(CH2)gCOOCH3
Figure 2.
Mass spectrum drawn in 1 3 minutes using the device described
From a spectrum obtained at 2 0 e.v. on an Atlas-Werke CH-4 mass spectrometer equipped with a gas chromatographic inlet system. The sample was the maior peak from a mixture of methyl esters of bacterial origin) the structure was assigned on the basis of this spectrum and that of the isopropylidene derivative of the corresponding diol (2). The tick marks for the mass numbers, relative abundance, and per cent of total ionization, and the lettering were added by hand.
the foot switch depressed as on the second trace with the w i t c h released. The timer is allowed to run until i t reads the mass number a t which reading of the spectrum is to begin. The readout chart paper drive is started at 1 inch per minute, and each peak of the spectrum is read by manipulating the Peak Height potentiometer and the foot switch during the intervals when the relay is grounded. The readout recorder produces a trace suitable for storage and study (Figure 2), while the integrator prints out a list of mass numbers and
relative intensities (in tenths of a per cent) which are comparable in accuracy to those measured manually. When the spectrum is completed, the Total button on the printer is pressed to give the total ionization in tenths of a per cent of the base peak. A number of possible modifications of this system suggest themselves. For example, if the chart drive of the readout recorder were arranged to advance in steps, a reproduction-quality spectrum might be obtained and, a t the same time, speed and accuracy could be
improved by providing switches t o permit stopping the system between peaks (for example when there is a large change in intensity), or by scanning rapidly through a region of no peaks. LITERATURE CITED
(1) Biemann, K., “Mass Spectrometry;
Organic Chemical Applications,” pp. 42-6, McGraw-Hill, New York, 1962. (2) McCloskey, J. A., McClelland, M. J., J. Am. Chem. SOC.87,5090 (1965).
WORK sup orted by National Institutes of Health &rant No. HE-05435.
Stainless Steel Capsule with Iron ”Window“ for Determining Hydrogen in Alkali Metal by Vacuum Extraction Joseph W. Glass, Chris M. Larsen, and James M. Scarborough, Atomics International, A Division of North American Aviation, Inc., P. 0.Box 309, Canoga Park, Calif. YDROGEN in alkali metals is normally H d e t e r m i n e d by a technique wherein the alkali metal sample is sealed in an iron capsule ( 1 ) and hydrogen is extracted by heating in a vacuum at 700750’ C. The total quantity of gas produced is measured and the hydrogen is converted to water which is trapped. The residual quantity of gas is measured and the hydrogen is determined by diff erence. Usually, the iron capsule which contains the alkali metal sample is sealed by welding. However, welding is very often inconvenient, expensive, and requires expert care to prevent contamination of the sample. A simple, time-saving technique has been developed in which the welding operation for each sample is eliminated by substituting a reusable stainlesssteel capsule having an iron “window”
942
0
ANALYTICAL CHEMISTRY
1
-IRON DISC, 10 mil THICK, NOMINAL, WELDED TO END OF REDUCER
-0.75
in. OD
u2Oin
Figure 1. sule
CROSS SECTION OF MODIFIED SWAGELOK REDUCER (3/41n TO5/16ih) AND 5/16 in PLUG (TYPE 316 S$
is welded over the large end of the reducer. The sample is transferred to the capsule in an inert atmosphere box and the plug fitting is sealed. The capsule is then placed in the hydrogen analyzer, with iron “window” a t the top, and the analysis is performed in the conventional manner. This technique has been used successfully for Ea, K, and Na-K samples. No capsules have ruptured or leaked and it has been demonstrated that the capsules may be cleaned and reused.
Hydrogen extraction cap-
for the iron capsule. The stainless steel capsule can be made from a commercially available Swagelok reducer and plug as shown in the Figure 1. A thin iron window (nominally, 10 mils)
LITERATURE CITED
(1) Pepkowitz, L. P., Proud, E. R., ANAL.CHEM.21, 1000 (1949).
WORK done under the auspices of the U. S. Atomic Energy Commission, Contract AT(ll-l)-GEN-S.
