this work are probably caused by the pressure difference between the two operations; MTA work being done at a factor of lo3 to lo4 lower pressure. This is particularly evident for a fast release of water a t about 310' C. and 10" torr (sharp peak in the MTA scan in Figure 4) as compared with a slow diffusion process a t lop3 torr [gradual increase in base line for both MDTA (mass spectrometric differential thermal analysis) scans]. The technique of MDTA will, then, be particularly useful in the study of pressure dependent thermal reactions.
monitor
DTA endolher m
MDTA
L
LITERATURE CITED I ~ I ' I ' I ' I ' I ~ I ' I ' I ' I ' I ' I ' I ' J ' I J' II
20 40
60
80
1 1 1
100 120 140 160 180 200 220 240 260 280 3 0 0 320 340 360:
TEMP..
Figure 4.
MgC12.6
OC.
HzO
( 1 ) E. I. du Pont de Nemours & Co., "900 Differential Thermal Analyzer," (2) Langer, H. G., Gohlke, R. S., ANAL. CHEM.35, 1301 (1963). (3) Nuclear Products modified 1-SA or unmodified 1-SX.
p.,
(4) Smith, D. H., Langer, H. G., The
reduce this volume and with this the time lag. Figure 3 compares the various runs. As a second example, MgC12.6HzO was studied, also a t a pressure of torr. Again, HzO a t m/e 18 was mbnitored. A comparison of the data from the MTA scan monitoring water
and from the combined instrumentation can be made by examining Figure 4. The apparatus functions quite well and will prove to be very useful in monitoring thermal decomposition products and phase changes in one operation. Discrepancies initially noted between the MTA and DTA scans in
Dow Chemical Co., Framingham, Mass., unpublished data, 1964.
HORSTG. LANGER ROLAND S. GOHLKE DENNISH. SMITH The Dow Chemical Co. Eastern Research Laboratory Framingham, Mass.
Determination of Americium-243 by Separation and Counting of Neptunium-239 Daughter SIR: A rapid, precise method was developed for determining low concentrations of AmZ43 in actinide-fission product mixtures. The determination is based on the separation and counting of ,56-hour Np239, the decay daughter of Am243. Although Am243is a n active a and y emitter, it is frequently encountered in systems in which its contribution to the total activity is so low as to make direct measurement by a or y spectrometry impossible. Methods involving the separation of Am from Cm and fission products are time consuming and require a n exacting technique. The mass spectrometric isotope dilution method reported previously by Banick, Carothers, and Donaldson (1) is the most precise of those that have been used in this work. However, the method not only requires the use of an expensive mass spectrometer, but requires chemical purification to obtain a sample that is very low in solids and 0-7 radioactivity. A convenient method for determining the concentration of Am243consists of separating and counting Np239, the product of the Am243a decay. The N p 434
ANALYTICAL CHEMISTRY
count at secular equilibrium (Np eq.) is compared with that of samples of known Am243concentration. EXPERIMENTAL
The &io Np eq./Am243was established by analyses of eight samples standardized by the mass spectrometric method referred to above. Samples
Table
I.
Ratio of Np239Activity to Weight of Am243in Solutions of Irradiated
Am24a (mg./ml.) 0.0173 0.0173 0.0173 0.0173 0.0173 0,1555 0,1555 0.1555
Average
were undisturbed for a t least twenty days to allow the Am243-Npz39system to reach equilibrium. Aliquots of the samples containing between 0.1 and 5.0 pg of .4mZ43were taken, and Np*39 was then extracted into 2-thenoyltrifluoroacetone (TTA) by the method of Murray ( 2 ) . Of the gamma emitters present (Zrg5-Nb95, Ce144-Pr144 C~134~137, Ru1O3P1O8),only Zrg5-Kbg5was kxtracted with the Np239. The extract was
Np23geq. (c./s./ml.) 2 . 0 1 x 104 1.98 1.93 1.98 1.96 7.0 6.8 6.8
Np939 eq. (c./s./mg.) AmZ43 1 . 1 6 X lo6 1.14 1.12 1.12 1.13 1.09 1.08 1.08 ~
~~
Pu239
Apparent" counting efficiency, 70 16 23 1.5 94
15.60 15.66 15 80 15 24 15.10 15.10
= 15.59 f 0 . 3 9
Np2sg c./s./mg. AmZ43 Apparent counting efficiency = 7.15 X lo6 d./s./mg. with TL/2Am243= 7950 years.
counted in a 5- X 5-inch NaI (TI) well crystal connected to a 256-channel pulse height analyzer. The portion of the y spectrum between 0.20 and 0.50 m.e.v., which included the 0.22 and 0.28 photopeaks, was used to calculate the Np239 count rate. This count rate was corrected for the contribution made by the Zr95-Xb95. DISCUSSION
Table I is a summary of the eight determinations that were made to establish the relationship between NpZ39 counts and Am243 concentrations a t equilibrium (Np eq./Am). The figure in column 4 is referred to as an “apparent counting efficiency,” since it also includes the errors involved in separating the Np. The results of Table I were then applied to the analyses of sixteen sam-
ples from laboratory scale studies of proposed processes for actinide-lanthanide separation and americium-curium separation. Where the age or history of the sample was uncertain, two extractions were necessary. The first Np extract was discarded and new Np was allowed to “grow in” for a specified time, usually about twenty-four hours. The “in-grown” Np was then extracted, counted, and corrected to equilibrium. The amount of Am243in the samples was also determined by the mass spectrometric method. The average recovery of AmZ43, when analyzed by separating and measuring its NpZ39daughter activity, was 99.5y0 of the value obtained by the mass spectrometric method. The relative standard deviation of an individual determination was =t3.3%‘,.
ACKNOWLEDGMENT
The author gratefully acknowledges the assistance of B. L. Bussey of the Savannah River Plant who performed the mass spectrometric determinations of Am243. LITERATURE CITED
( 1 ) Banick, C. J., Carothers, G. A , , Donaldson, W. T., ANAL. CHEY. 35, 1312 (1963). (2) Murray, B. B., c’. S . At. Energy Comm. Revt. DP-316.SeDtember 1958.
C ~ R IJ.L BAXICK Savannah River Laboratory E. I. du Pont de Nemours & Co. Aiken, S. C. The information contained in this article was developed during the course of work under Contract AT(07-2)-1 with the U. S. Atomic Energy Commission. ’
Mass Spectrometer Used as Detector and Analyzer for Effluent Emerging from Capillary Gas Liquid Chromatography Column Sir: One of us (6) recently described a combination mass spectrometergas chromatograph which employed two molecular separators coupled in series between the column and the inlet line of the mass spectrometer. With this technique, the sample-to-helium ratio is increased a t least 100 times, and good spectra were obtained from less than 1 pg. of material. This communication describes the extension of this combination instrument to capillary gas liquid chromatography columns. The increase in resolution normally obtained with capillary columns is extremely useful in analyzing mixtures of compounds having similar properties-Le. , the fatty acid esters, C I S , CIS:^, CIS:^, and C18:3. With this combination instrument, capillary or packed columns can be used without modification of the inlet system of the mass spectrometer. The time required to change from a packed column to a capillary column is less than 1/2 hour. Other differently designed combination instruments using capillary columns have been described (1, 3, 4, 6), but attention has been directed chiefly to the analysis of compounds with low molecular weight. EXPERIMENTAL
Apparatus. The arrangement used for connecting the capillary column to the mass spectrometer varies from that previously reported (6) in that only one molecular separator is used and that a part of the total ion current is collected on a plate in the analyzer tube rather than in the source. Continuous registration of the total ion current serves
** M
354 /
as the gas chromatographic record. The helium pressure at the sample inlet side was in most cases 1.0 kg. per sq. cm., giving a flow rate of about 0.5 ml. of He per minute. The operating temperatures were: ion source, 250” C.; injection port, 285’ C. The column was run either isothermally or programmed linearly. The temperature programmer was the same as that used karKer ( 5 ) . GLC Column. h 90-foot stainless steel capillary column, 0.01-inch i.d., 20% diethyleneglycolsuccinate (DEGS) (Applied Science Laboratories, State College, Pa.) supplied by M.E. Mason, Oklahoma State University, was used. Methyl undecanoate was obtained from Applied Science Laboratories. I t was equipped with a 7 :1 precolumn split device. Methyl esters were prepared from peanut oil by the method of Mason, Eager, and Waller (2). The samples were injected onto the GC column in 0.1 to 0.5 jd. of redistilled acetone. Temperatures above 170’ C. were avoided because of excessive bleeding. RESULTS A N D DISCUSSION
-
* . d Figure 1 . High mass end of mass spectrum of compound identified as docosonoate Galvanometers sensitivity ratios, 1 : 10: 100
Figure 1 shows the high mass end of the mass spectrum of docosanoate from the iniection of 10 fig. of peanut oil methyl esters. The peaks in the m/e 333 region are caused by column bleeding. This spectrum was recorded when the concentration was less than 0.2 pg. [calculation based on the average content of docosanoate in peanut oil @)], the retention time was 46 minutes, and the GC peak height was 32 mm. The most sensitive galvanometer deflection was 470 mm., which indicated that the molecular ion of a mass spectrum taken VOL. 37, NO. 3, MARCH 1965
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