shared peaks are available. Nevertheless, difficulties may be encountered when impurities or defects in the lattice affect the line broadening. Also, a relatively small weight fraction of large crystallites may sometimes prejudice the results toward larger crystallite size. The value of the method for each new system would have to be verified. For the 5.67y0 palladium on yalumina sample, a well defined unshared peak is obtained for palladium a t the spectrometer angle 82.4' (using
copper target tube). In cases where the component is present in concentrations too low to be detected by this technique, it becomes necessary to use slower scanning or stepwise counting. However, some of the industrial advantage of the method is lost when the calculation cannot be made from a control-type x-ray pattern. LITERATURE CITED
(1) Allred, V. D., Buxton, S. R., McBride, J. P., J. Phys. Chem. 61, 117-20 (1957).
(2) Gruber, H. L., ANAL. CHEM. 34, 1828-31 (1962). (3) Mug, H. P., Alexander, L. E., "X-Ray Diffraction Procedures," p, 511, Wiley, New York, 1954. (4) Van Nordstrand, R. A., Lincoln, A. J., (1964). Carnevale, A., ANAL.CHEM.36, 819-24
W. M. KEELY Girdler Catalysts Depart. Chemetron Chemicals ChemetronCorp. Louisville, Ky.
Low-Retention-Time Gas Chromatographic Analysis of Pentene Isomers SIR: Inexpensive packed columns for gas-liquid chromatography continue to prove most attractive for on-stream analysis of laboratory-scale or pilotplant reactor effluents. Recently we have found that polyglycol-packed columns are most effective in separating mixtures of six isomers of nentene in 15 minutes. Such short analytical
P-l
W v)
2
times permit one to follow rapid changes in catalytic activity, a necessary part of meaningful studies of catalysts. Mixtures of the six isomers containing approximately equal amounts of each isomer were analyzed on a polyglycol column with short retention times so that sampling was possible every eight minutes. Longer times (50 minutes) were required for mixtures containing over 95Q/, pentene-1 because of tailing by the pentene-1 peak; but in the absence of 2-methylbutene-l,15 minutes were adequate. Polgar, Holst, and Groennings (4) used a capillary column to separate pentenes in 23 minutes after sample charging. Although packed columns with solvents such as dimethylsulfolane and diisodecylphthalate have been used for pentenes, short times have not been reported (1, 3). Silver nitrate has been used for separating hydrocarbons a t short retention times, but all pentene isomers have not been studied (2).
0
O W
k W P
v)
K
K
0 IO
W W I-
n
I
0
1
t
4
e
8
IO
TIME (MINUTES)
Figure 2. Separation of pentene isomers on silver nitrate column Column, 6 feet by l / 4 inch; 23' C.; helium, 30 cc./minute
The chromatographic apparatus used was a Perkin-Elmer Model 154D Vapor Fractometer with a Brown Electronik recorder equipped with a Disc chart integrator. This apparatus has a temperature-controlled oven (ambient to
225' C.), a thermal conductivity detector with thermister beads, and a recorder sensitivity variation of 1 to 512 for obtaining well defined peaks.
v) W
8 I-
n W
EXPERIMENTAL
n
a
W
6
Table I.
Comparison of Retention Times
He flow rate,
Press. Column cc./ Temp., drop, designation min. ' C. p.s.1. 3MB-1 6-foot 6
8
10
IL
Figure 1 . mers on polypropylene glycol column
148
ANALYTICAL CHEMISTRY
21LIB-1
tP-2
cP-2
2MB-2
I4
TIME (MINUTES) Separation of pentene iso-
Column, 20 feet by '14 inch; 25' C.; 48 cc./rninute
P-1
x
helium;
AgN03 20-foot x
1/4-inch PPG
33
24
3.6
6.2
7.3
6.2
3.3
8.2
2.8
30
26 40 26
12.0 12.3 16.7
10.2 8.3 7.2
13.1 10.3 9.4
14.2 11.0 10.2
15.3 11.7 11.0
16.3 12.3 11.7
17.8 13.2 12.7
50
The columns tested were the following: (1) 6-foot X 1/4-inch silver nitrate (AgN03) column. A 6-foot, W-shaped column made of l/d-inch copper tubing and packed with a 25 wt. % mixture of 30 wt. % silver nitrate and 70 wt. % ethylene glycol on 80- to 100-mesh chromosorb. (2) 20-foot X l/r-inch polypropylene glycol (PPG) column. A 20-foot coiled column made of 1/4-inch copper tubing and packed with 30 wt. % polypropylene glycol (average molecular weight approximately 550) on 60- to 80-mesh C-3 firebrick. The column packing was obtained from W. H. Curtin & Co. Each of the pentene isomers was obtained from Phillips Petroleum Company in the form of pure grade (99yo min.) chemicals except for the pair of pentene-2 isomers in which case a pure grade mixture was obtained.
Helium was used as the carrier gas in all runs.
markedly in performance after repeated on-stream use.
RESULTS
LITERATURE CITED
Chromatograms for the polypropylene glycol and silver nitrate columns are presented in Figures 1 and 2, respectively. Retention-time data are assembled in Table I. Clearly, the polypropylene glycol column affords a useful means for separating all the isomers of peiitene in a short time. Although retention times are small in the silver nitrate column, 3 methylbutene-1 and 2 methylbutene-1 could not be resolved. This does not preclude its use for following double-bond shift isomerizations, but the silver nitrate column appears to decline rather
(1) Bednas, M, E., Russell, D. S., Can.J. Chem. 36,1272 (1958). (2) Fredericks, E. ?VI., Brooks, F. R., ANAL. CHEY.28, 297 (1956). (3) Knight, H. S., Zbid., 30,Q(1958). , (4) Polgar, A. G., Holst, J. J., Gi>ennings, S.,Ibid., 32,336 (1960).
DELBERT &I. OTTMERS~ GEOFFREY R. SAY* HOWARD F. RASE Department of Chemical Engineering University of Texas Austin, Texas Present address, Esso Research and Development, Baytown, Texas. Present address, Esso Research and Development, Baton Rouge, La.
Quantitative Analysis of Helium-3 by Gas Chromatography SIR: The separation and quantitative analysis of permanent gases by gas chromatography using adsorption columns is well known (4). Since 1956, techniques have been known for the separation of the isotopes of hydrogen ( 7 ) , although the quantitative analysis reported by Phillips and Owens remains difficult (8). The quantitative analysis of the mass number three isotope of helium is reported in the present work. EXPERIMENTAL
The apparatus has been described previously (3). An 8-ft. long 0.180-inch i.d. stainless steel column filled with a 24to 50-mesh Linde 5A Molecular Sieve is operated a t 100' C. The coLumn is activated by heating it to 220' C. for 1 hour while He4 gas flows through it. The thermal conductivity detector is operated as a bridge circuit with a constant current of 400 ma. The bridge imbalance is measured directly on a 1-mv. full scale potentiometric recorder and may be attenuated by up to a factor of 1000. He4 carrier gas is
4
.
p
o
The elution of He3 as a distinct peak under the conditions just described is shown in Figure 1 for a sample pressure of 0.49 p.s.i.a. and a He3partial pressure of 0.26 p.s.i.a. A nearly symmetrical elution peak is obtained indicating a linear adsorption isotherm. The introduction of He3 a t varying pressures and concentrations in He4 allows a calibration curve of output voltage us. volume-
I
0.10
I
0.m
I
OJO
i
aa
1
0.50
I 0.w
1
a70
0 0.0
B R I D E IMBALANCE, MILLIVOLTS
Figure 1.
Elution of Hea
Column temperature, 100' C.; flow rate of He4 carrier, 24 atm. ' 0 C. cc./min.; bridge current, 400 ma.; attenuation, 5. Peak is negative with 2 peak shown a t attenuation of 1. To i s time of sample respect to 0
introduction
tric concentration to be obtained. The slope of this linear curve is 0.000196 mv. per p.p.m. (volume) a t the above column conditions. In the same units the sensitivities of O2 and N2 for this column a t the above conditions are 0.00192 and 0.00168 mv. per p.p.rn., respectively. The sensitivity of the column to H2is 0.0000624mv. per p.p.m. The separation of Hz and He3 peaks is indicated in Figure 2. This chromatogram was obtained a t a column temperature of 40' C. Analyses are possible when the H2-He3 ratio is as large as 1000. The gas chromatographic analysis of He3 is sensitive enough to detect small leaks in systems containing He3 as well as to monitor the purity of He3 to such likely contaminants as the permanent gases.
i
CHROMATOGRAPH CONDITIONS T. IDQ.0 I *4OOrno P*2Spsig
p
o
RESULTS
H:P.0.49 piin CONCENTRATION-OF Hfa533
0,
I14!
supplied a t a flow rate of 34.6 ml. (1 atm., 0' C.) per minute. Small volumes (about 5 std. cc.) of He3-He4 mixtures were obtained. A mass spectrograph analysis had been made of the He3-He4 ratio. The sample volume to the chromatograph is 1 cc. and the sample inlet pressure is measured with a Wallace and Tiernan gauge.
'
I
o
TO
I ai0
0.~0
o . ~
.I,
o . ~
a~
a
D
BRIDGE IMBALANCE, MILLIVOLTS
Figure 2. Separation of eluted peaks of Hz and Hea at column temperature of 40" C. and other conditions as described in text Large hydrogen concentration can b e inferred from reversed height ( 4 )
VOL. 38, NO. 1, JANUARY 1966
0
peak
149
