Rapid Separation of Xylenes and Ethylbenzene by Gas Chromatography Using Packed Columns SIR: Since the introduction of gas chromatography, many analysts have been looking for a substrate which will give a practical separation of xylenes and ethylbenzene on packed columns. Several liquid phases (1, 3) have been investigated for this application. The best separations on liquid phases have required long columns with corresponding long retention times which might be considered prohibitive for routine control work. Recently, Van Rysselberge and Van Der Stricht (2) reported the use of Bentone 34, an organo clay complex as a substrate for the separation of these compounds. Although a good separation of the isomers was achieved on a 275cm. column, the total analysis time was 60 minutes. Furthermore, an extremely small sample size (0.025 pl.) and low temperature (43' C.) were used to effect the separation. A separation of the xylenes and ethylbenzene equivalent to that reported in (2) has been obtained in a shorter time with considerably more latitude in operating conditions by modifying Bentone 34 with an equal amount of diisodecylphthalate. Figure 1 shows a separation of the constituents in commercial xylene in just 12 minutes on this modified phase. EXPERIMENTAL
Apparatus. An F & M Model 609 flame ionization gas chromatograph equipped with a MinneapolisHoneywell 1-mv. recorder was used in this work. The column was a 6foot x 8/le-inch 0. d. stainless steel tubing packed with 5% Bentone 34 5% diisodecylphthalate on 60- to 80-mesh Chromosorb SI7.
+
Operating Conditions Column temperature, "C. Injection port temperature, "C. Detector temperature, C. Helium flow, cc. per minute Hydrogen flow, cc. per minute Air flow, cc. per minute Range Attenuation Sample size, 4.
75 200 100
ANALYTICAL CHEMISTRY
@ ETHYLBENZENE @ P XYLENE @ M XYLENE @ 0 XYLENE
c
5
I
cc
c
3
n
50 K w P K
8 K
0
TIME (MIN.) Figure 1.
without special treatment. One-half gram each of Bentone 34 (National Lead Baroid Division, Houston, Texas) and diisodecylphthalate were dissolved in 100 ml. of benzene and slurried with 9.0 grams of support. The solvent was evaporated slowly on a hot plate with constant stirring until the packing was dry. A straight length of stainless steel tubing 6-foot X S/+nch 0 . d. wa,? filled with this material, plugged a t each end with glass wool and coiled to fit the column housing. The column was conditioned at 150' C. for approximately 30 minutes, then set a t an operating temperature of 75" C. DISCUSSION
400
The order of elution on Bentone 34 alone is ethylbenzene, para-, ortho-, and meta-xylene. Addition of diisodecylphthalate causes the ortho isomer to elute last. If a greater proportion of diisodecylphthalate is used, better separation of ethylbenzene and ortho-xylene is obtained, but a corresponding decrease in meh-para resolution results. Equal amounts of each substrate have
60
100 256 1.o
12
Chromatogram of commercial xylene
100
Column Preparation. The column packing was prepared by the conventional slurry and evaporation technique using benzene as a solvent. Either Chromosorb, Celite, or Firebrick may be used as the support 592
0 TOLUENE
been found to give optimum relative resolution. Although this work was performed on a flame ionization instrument, equivalent separations have been obtained with thermal conductivity equipment. The unique selectivity of Bentone 34 for the isomers of xylene suggests that it might also be useful for the separation of other aromatic mixtures. Preliminary investigation indicates that in combination with a suitable liquid phase Bentone 34 may be equally effective in resolving xylenols and methyl naphthalenes. LITERATURE CITED
(1) Case, L. C.,
J. Chromalog.
6, 381
(1961). (2) Van Rysselberge, J., Van Der Stricht, M., Aruture 193, 1281-2 (1962). (3) Zlatkis, A., Ling, Su-Yu, Kaufman, H. R., ANAL.CHEM.31, 945 (1959).
SUUEL F. SPENCER F & M Scientific Corp. Starr Road and Route 41
Avondale, Pa.
