the degree of separation is less good. The curves shown in Figure 2 , and others not shown, indicate that the first distillate of the more volatile of the two is nearly pure, but that the last portion of the component (near the summit of the peak) is contaminated with some of the less volatile substance* After the peak for the first substance has been passed, almost none
of that substance is found in the second component. Cuives in Figure 2 show that a relatively runall amount of either a more volatile cIr a less volatile component of a mixtuie is detected during a distillation. LITERP'IURE CITED
(1) Baker, C. A., Williams, R. J. P., J . Chem. Soc. 1956, 2362.
(2) bfika, G., Cady, G. H., J . A m Clwn.
S°C*~l*lpress*
H. CADY GEORGE DAVIDP. SIEOWARTH Department of Chemistry University of Washington Seattle 5, Wash. RECEIVED for review October 16, 1058. rlccepted January 19, 1959.
Gas Chromatography of Hydroccirbons Using Capillary Columns and Ionization Detectors SIR: The use of coated capillaries as columns for gas chromatographic separations was first reported by Golay (2) in 1957. While his initial work showed relatively low separating efficiencies of 40 theoretical plates per foot, he recently reported (8) efficiencies up to 333 plates per foot. The detector used by Golay mas a thermal conductivity cell with thermistor beads. Dijkstra and de Goey ( I ) used capillary columns, but with considerably less success. The current development of a highly sensitive detector by Lovelock (5) has prompted a further study of capillary columns. The detector used in this work has as the basis of its mode of operation the unique ionization properties of argon, and is sensitive enough to detect 1 X lo-'* mole of most organic compounds. To use capillary columns effectively, changes in the original cell design (4) mere made. The cell volume \vas reduced to 1 ml. and the cell modified to permit an additional flow of argon to enter it. The ancillary equipment was that of a Barber-Colman, RIodel 10. Flow rates were adjusted so that the gas rate enter-
ing the cell from the capillary colunin was on the order 3f 0.5 ml. per minute, while the additicrial argon flow from the other end of the cell was about 25 ml. per minute. 13y having a relatively large backsweep cd carrier gas over the column eluent, thib latter is forced down along the sides of ihe inlet tube, producing an effective cell volume of only a few microliters. A 100-foot coplJer capillary column with an internal diameter of 0.01 inch was coated with s -palane in the following manner. The column mas completely filled with a 10% solution of squalane in chloroi orm by applying pressure a t the front eiid of a small tube connected to the capillary and containing about 5 nil. of thc solution. After the solution is blown Ihrough the column, the volatile solvenl evaporates, leaving a thin coating of uniform thickness. The use of coated capillaries necessitates the introdL ction of minute sample quantities to s void overloading the column. A simple gampling device consists of arranging a bypass tee just below the point of injecion. Tubing diameters can then be adjusted to allow 99.9% or more of the sample to vent to the atmosphere. Sam ,le sizes in the micro-
liter range can be handled in this manner with reproducible results. The maximum load for capillary columns appears to be 1 y for a mixture which resolves into 10 components. The apparatus described has been useful in analyzing complex hydrocarbon mixtures. Figure 1 illustrates the resolving power of capillary columns on a sample containing Cj to Ce paraffins and naphthenrs. Tn-enty-five components are clearly resolved in 00 minutes. Both the column and the cell were operated a t 100" C. and a pressure of 6 p.s.i. argon was used on the capillary. The calculated theoretical plate efficiency for the n-heptane peak is about 50,000-that is, 500 plates per foot. Efficiencies up to 750 plates per foot have been obtained on hydrocarbon mixtures by using this column. The combination of very efficient coated capillary columns with highly sensitive ionization detectors has made possible the resolution of isomeric compounds which previously have been separated only by using specific liquid phases. Scott (6) has prepared chromatographic columns of high efficiencies packed with
I . 13
Figure 1 . 2-MB. 2.Methylbutane n-Pent. n-Pentane 2,2-DMB. 2,2-Dimethylbutone CP. Cyclopentone 2,3-DMB. 2,3-Dimethylbutone 2-MP. 2-Methylpentane 3-MP. 3-Methylpentone n-Hex. n-Hexane MCP. Meihylcyclopentane
620
ANALYTICAL CHEMISTRY
20
39
??ME
50
,
MINUTES
60
70
80
w
Chromatogram of a hydrocarbon mixture using a 1 00-foot capillary column 2,2-DMP. 2,2-Dimeth:dpentane CH. Cyclohexane 2-MH. 2-Methylhexar 1,l-DMCP. 1,l-Dirneiiylcyclopentane 2,3-DMP. 2,3-Dirneth:dpentone 3-MH. 3-Methylhexar G 1 ,tr-3-DMCP. 1 -trans- 3.dimethylcyclopentane 3-EP. 3-Ethylpentane n-Hept. n-Heptane
1,cis-2-DMCP. I-cis-2-dimelhylcyclopentane 1,1,3-TMCP. 1,1,3-Trimethylcyclopentane MCH. Methylcyclohexone 2,2-DMH. 2,2-Dimethylhexane ECP. Ethylcyclopentane 1 ,tr-2-cis-4-TMCP. 1 -trans-2-cis-4-trimethylcyclopentane 3,3-DMH. 3,3-Dimethylhexane
C-22 insulating brick, and resolved complex mixtures with nonspecific liquid phases. The capillary column-ionization detector system has been used in thc resolution of the following mixtures:
ACKNOWLEDGMENT
The authors thank D. H. Desty, British Petroleum Co., Ltd., for invalua.ble advice on coating and loading
columns.
All 16 of the CSto CTparaffins
(1) Dijkstra, G., de Goey, J., Second Symposium on Gas Chromatography, Amsterdam, May 20, 1958. ~ J. l E,,~'(Gas ~Chromatog, (2) ~ raphy, ed. by V. J. Coates, p. 1, Academic Press, New York, 1958. (3) Golay, ill. J. E., Second Symposium on Gas Chromatography, Amsterdam, May 20, 1958.
C , olefins All 16 of the CI to Cgalcohols Aqueous solutions of Cp to C5 aldehydes
y.
Stationary liquid phases and operating parameters for capillary columns are now being investigated.
Determination of Trace Organic Impurities in Concentrated Hydrochloric Acid by Extraction with Carbon Disulfide
_
_
Range ppm
_
~
_
or Y
B.L.
Slit (mm) AA or
Pts.
Av
mm
_
13.2 0.180 2.0 13.0- 0.035 13.25 -~~ 0.180 2.0 CH2Clr 0-200 fl 13.5 13.3- 0.035 13.65 CHCl3
Chloroform
Methylene chloride
0-200
f l
1, I -Dichloroethane
9.5 9.259.6
0.300 0.064
2.0
1,Z-Dichloroethane
14.0 13.814.2
0.750 0.132
2.0
12.8 12.412.9
Carbon tetrachloride
0.450 0.081
0.89
0.77
Relative absorbances are given as the slope of the Beer's law concentration curves used expressed in terms o f absorbance per 100% of constituent.
Determination of Thianaphthene in Naphthalene R. E. SEEBER ond R. G. WHITE, Notional Aniline Div., Allied Chernicol Cotp., Buffalo, N. Y.
No. -
Component Name Formula Thianaphthene
C8HsS
cs-73
Slit
Concn.
(mm)
mgfml
Range
Accurocy
A orv B.1.
AX or
Length
%
%
Pis.
AV
mm
0-5
&0,2
14.5 14.314.9
2.8
200 0.5
Insfrumenf: Baird-Atomic, Model 8, NaCl prism Sample Phase: Solution in cyclohexane Base l i n e - L
Inverse matrixGraphicalL
PointCell Windows: NaCl Absorbance Measurement:
Successive approx.-
Relative Absorbances'-Analyticol Matrix: Component/X 13.2~ 13.5~
4 5
4 5
The analytical wove lengths are so ch9sen that interfering absorptions are practically negligible. The lower limit of detection is 1 p.p.m.
Calculotion:
1 2 3
3
0.84 0.38 0.59
2
1
Calculation:
RECEIVEDlor review December 2, 1958. Accepted Jmuary 2, 1959.
Component
2.0
Instrument: Perkin-Elmer Model 12C, NaCl prism Sample Phase: Concentrated hydrochloric acid extracted with carbon disulfide Cell Windows: NaCi Absorbance Measuremenf:
J. E. LOVELOCK Departme~ltof Internal Medicine Yale U n i v d t y School of AIedicine New, Haven, Corm.
Extraction recovery constonts for the various components are as follow fraction recovered):
CS-72 Concn. see comments) length
X
Department of Chemistry Universitj of Houston Houston, 'rex
1
H. 1. SPELL and J. N. LOMONTE, The D o w Chernicol Co.,
freeport, Texos
Accuracy ppm
(19:s). (6) Scott, R. P. W., Second Symposium on Gas Chromatography, Amsterdam, hlay 21, 1058. -4LBERT ZLATKIS
LITERATURE CITED
p - and m-xylene
Componer Formula Name
(4)Lipsky, S. R., Lovelock, J. E., private corn munication. (5) Lovelock, J. E., J. Chroljzatogr., 1 , 35
9.5p
Base line-&-
Inverse . i rm ta GraphicalX
Point--
Sucwssive approx.-
14.0~ 12.8~ Relative Absorbances-Analytical Matrix: Componentf A
1352 680
1
234 320 892
Materiol Purify: Reference compounds 99+% pure Comments: Two hundred fifty milliliters o f the acid sample i s extracted with 5 ml. o f CSz. This i s repeated, using on additional 5 ml. of CSz. The two CSz extracts are combined, mixed, and analyzed.
14.5 10.2
Maturity Purity: Naphthalene 9 9 +yo, tliianaphthene 95%, Matheson, Coleman and Bell No. 7507. Comments: Absorbance measured vs. NaCl compensating plate. Includes solvent absorbance which is negligible. Armstrong, Densham, ond Gough (J. Chem. SOC. 1950, 3359) descrihe use of molten naphthalene and o different (much weaker) thianaphthenc band for this analysis.
VOL. 31, N3. 4, APRIL 1 9 5 9
621
