analysis of 6 ml. of adrenal extract, shows that the column is overloaded under the conditions used (linear gradient, concentration change of 0.333% per tube). Yet, this amount of sample is required for the determination of small peaks, such as those occurring betmeen B and E and between E and F. The problem was solved by programming the gradient elution as shown in Figure 7 (top). To save time, compounds A, S, and B were deliberately eluted in a single peak, while increasing the resolution of subsequent compounds, particularly the BT-reducing compound between E and F. This compound was shown by thin-layer chromatography to be Reichstein's Compound D (allopregliane - 38,17c~,21- triol - 11,20 - dione). Tlius, any portion of the elution pattem can be selectively compressed or cs-
panded by programmed gradient elution. The steroid analyzer ( 1 ) is a prototype instrument, representing a considerable investment of time and cost. The degree of automation achieved probably exceeds the requirements of a routine laboratory. However, the principle of gradient elution and particularly polarity reversal will undoubtedly be found generally useful for difficult resolution problems and may be applied either manually or by a simple combination of tape programming and dual pumping. Details of this simplified system will be described elsewhere.
Frank 0. Anderson, Grant C. Riggle and John K. Cullen, Jr., Instrument Engineering and Development Branch, Division of Research Services. They thank William J. Haines, Upjohn Co., for the generous gift of beef adrenal extract. LITERATURE CITED
(1) Bnderson, F. O., Crisp, L. R., Riggle,
ACKNOWLEDGMENT
G. C., Vurek, G. G., Heftmann, E., Johnson, D. F., Francois, D., Perrine, T. D., ANAL.CHEM.33, 1606 (1961). ( 2 ) Bennett, R. D., Heftmann, E., J . Chromatog. 9,348 (1962). (3) Heftmann, E., A N A L . CHEM.34, 13R (1962). (4) Heftmann, E., Johnson, D. F., Ibid., 2 6 , 519 (1954).
Tlic authors gratefully ackiioivlcdge the technical advice and assistance of
I ~ L C L ~ V for L D review Ma\ 16, 1903. .Iccepted Yepteinber 16, 19G3.
Qua ntitative Analysis of Aromatic Hydrocarbons by Capillary Gas Chromatography JOHN Q. WALKER' Barber-Colman Co., Pasadena, Texas DAN L. AHLBERG Research Division, Signal Oil and Gas Co., Houston 72, Texas
b The use of polar substrates with capillary columns has made the separation o f m- and p-xylene less difficult. m Bis(m phenoxyphen0xy)benzene (b.p. 273' C. at 1-mm. pressure) can b e utilized as a capillary column substrate for quantitative analysis of c6 through CI aromatics. If base line separation in the c6 through CS region i s desired, modification of the liquid phase with squalane i s required. Comparative elution data and spectra of several polar substrates are given Reliable quantitative analytical data in this aromatic range can b e obtained using these columns in a gas chromatograph employing a linear sample splitter and high temperature flame ionization detector. This investigation includes over 30 available compounds in the c6 through c11range. Twentyfive of the first 28 aromatics were resolved in 17 minutes using this method.
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results of the authors' investigation of several liquid phases are given in Table I. The present paper deals with the utilization of m-bii(m-phenoxyphen0xy)benzenc (EPB) (b.p. 273" C. at I-mm. preziure) as a capillary substrate. Thiq material is easy to coat on capillary columnh, is very stable, and can be utilized for the analysis of CS through C,, aromatics. If better than 90% separation in the C6 through CS region is desired, modification with squalane (a relatively nonpolar substrate) is required. This, however, limits the ~
Table 1.
T
1 Present address, Wilkene Instrument and Research, Inc., Houston, Texas.
2022
ANALYTICAL CHEMISTRY
Apparatus. Barber-Colman Model 20 a n d LModel 61-C instruments equipped with linear stream splitters
Liquid Stationary Phases Investigated for Aromatic Separations
.Iromaticparafin resolution B,P'-C)xydiprupioiiitrile Carbowax 1500 (1 00 )
analysis of aromatic hydrocarbons has been studied by a number of workers ( I - @ , and in the last three years the use of capillary columns has made the separation of nz- and p-xylene less difficult. The
EXPERIMENTAL
~~~~
Oxvbis-Zethyl benzoate with (;E96
HE
column to this particular range because of excessive elution time for higher boiling materials. A discussion of column preparation, operating parameters, etc., illustrates that reliable quantitative analytical data in the Cg through Cli aromatics range can be obtained using this column system on a gas chromatograph employing a linear sample splitter and ionization detector.
m-Bis(m-phenoxyphenoxy )benzene with squalane m-Bis(m-p henoxyphenoxy )benzene Rating system. 1. Poor 2 . Fair 3. Satisfactory 4. Excellent
Sylene rcsolutioii
Thcrd Y tnbili t y
b Figure 1 . Chromatogram of typical refinery 5 ' F. xyleiie fraction on modified BPB
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;ie
a
? X
P) W
XI
70' C., 2.9 ml./min. helium flow
P
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