October, 1983 SHORT PAPERS 1265

Separation of Dichlorophenol Isomers by Gas = Liquid Chromatography

Aoi Ono Defiartment of Chemistry, Faculty of Education, Niigata University, Niigata 950-2 1, Japan

Keywords : Gas - liquid chromatography ; dichlorophenol isomer separation ; dibenzo-l8-crown-6

The gas-chromatographic analysis of dichlorophenol isomers as the free phenol have been previously described.l-' Despite the difficulty of the analysis of these isomers as the free phenol, excellent resolutions using a modified Bentone-34 liquid stationary phase with mannit018 have been reported. Recently, an effective liquid stationary phase, dibenzo-18- crown-6, was found and important results concerning its application to the separation of dichlorophenol isomers have been obtained.

Experimental Stationary Phases

The following chemicals were all of Pure grade, unless stated otherwise, and used without further purification. The crown ethers dibenzo-18-crown-6, dicyclohexyl-18-crown-6 and 18-crown-6, were obtained from Nippon Soda Co. Ltd (Tokyo, Japan) ; silicones KF-54, KF-53, KF-56, KF-50 (phenylmethylpolysiloxane), KF-965 (methylpolysiloxane) and FL-100 (trifluoropropylmethylpolysiloxane) were obtained from Shinetsu Chemical Co. (Tokyo, Japan) ; silicone SH-7 10 (50% phenylmethylpolysiloxane) , was obtained from Torey Silicone Co. Ltd. (Tokyo, Japan) ; and dioctyl phthalate (DOP) and terephthalic acid of guaranteed grade were obtained from Nakarai Chemical Co. (Kyoto, Japan). Terephthalic acid was further purified by recrystallisation.

Samples

purified prior to use. Dichlorophenol isomers of Guaranteed grade from Tokyo Kasei Co. (Tokyo, Japan) were

Apparatus

was used. A Shimadzu, Model GC-5A, gas chromatograph equipped with a flame-ionisation detector

Chromatographic Procedure The separation column was a 2.25 m x 3 mm i d . stainless-steel U-tube packed with acid-

washed firebrick C,, (60-80 mesh) support (Johns-Manville, Denver, CO, USA) coated with 20% m/m of the stationary phase, The column and injector temperatures were 140 and 270 "C, respectively. Nitrogen was used as the carrier gas at a flow-rate of 25 cm3 min-l.

Results and Discussion As previously discussed: it is very tlificult to analyse dichlorophenol isomers as the free

phenol by gas - liquid chromatography. Harry and Normans reported this difficulty and separated the isomers as their methyl ethers. Modified Bentone-34, with sorbitol or mannitol, was the most effective, and Bentone-34 with rnannitol provided an excellent separation and base-line resolution.8

Adenosine, inosine, 2,4,7-trinitroAuoren-9-one and polyethylene glycol 1540, etc.,lo--12 which gave effective resolutions of xylenol isomers, did not provide an effective separation of di- chlorophenol isomers. In contrast, dioctyl phthalate,13Ja efiective for the separation of cresols and xylenols, was examined and appreciable resolutions were obtained8 for which the data are given in Table I.

Subsequently, terephthalic acid was examined as a possible separation medium because a

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1266 SHORT PAPERS Analyst, Vol. 108 TABLE I

RELATIVE RETENTION' OF DICHLOROPHENOL ISOMERS

Relative retention* I 2,6-Dichloro- 2,5-Dichloro- 2,4-Dichloro- 2,J-Dichloro- 3,5-Dichloro- 3,4-Dichloro- , 2,6-dichlorophenol/ Retention time of A

Stationary phase phenol phenol phenol phenol phenol phenol min Terephthalic acid . . . . 1.25 1.00 1.00 1.06 2.97 3.67 Silicone KF-50 .. . . 1.14 1.00 1.00 1.00 2.64 3.07 Silicone KF-53 . . .. 1.20 1.00 1.00 1.08 2.68 3.33 Silicone KF-54 . . . . 1.26 1.00 1.00 1.10 2.79 3,55 Silicone KF-56 . . .. 1.18 1.00 1.00 1.07 2.77 3.23 Silicone KF-965 . . . . 1.16 1.00 1.00 1.00 2.67 3.00 Silicone FL-100 . . . . 1.30 1.00 1.00 1.00 2.25 3.05 Silicone SH-710t . . . . 1.28 1.00 1.00 1.12 2.48 3.13 Dibenzo-18-crown-6 . . . . 1.00 1.08 1.23 1.42 8.50 12.50 Dicyclohexyl-18-crown-6 . . 1.00 1.10 1.10 1.16 8.32 11.24 18-Crown-6 . . . . 1.00 1.00 1.00 1 .oo 4.76 7.12 Dioctyl phthaiite . . . . 1.00 1.04 1.04 1.11 5.10 -

* Relative to retention time of 2,6- or 2,5-dichlorophenol (Le . , to the shortest retention time). t At 170 "C.

8.60 8.40

10.80 14.20 8.90 5.90 2.65 9.40 2.40 5.00 1.70

14.30

strong hydrogen bonding interaction would be expected (Table I). Although the 2,4- and 2,5-dichlorophenol isomers could not be separated using terephthalic acid, it provided some appreciable resolutions. Likewise, the crown ethers dibenzo-18-crown-6, dicyclohexyl-18- crown-6 and 18-crown-6 were examined ; dicyclohexyl-18-crown-6 did not resolve the 2,4- and 2,5-isomers, 18-crown-6 separated only the 2,3-, 33- and 3,4-isomers but dibenzo-18-crown-6 resolved all the isomers and provided appreciable resolutions.

As a result, it was postulated that the oxygen atoms arranged in the six-membered ring in hexaoxacyclooctadecane (cyclic oxygens) is effective in the separation ; further, it was per- ceived that phenyl groups play an important role in their analysis. Fig. 1 shows effective separations of dichlorophenols on dibenzo-18-crown-6.

Silicones KF-54, KF-53, KF-56 and KF-50 are phenylsilicones and their phenyl contents are as follows : KF-54, ca. 25%; KF-53, ca. 20%; KF-56, ca. 18%; and KF-50, ca. 5%. Silicones KF-50, KF-965 and FL-100 could not resolve 2,4-, 2,5- and 2,3-isomers.

Silicones KF-54, KF-53 and SH-7 10 gave appreciably effective resolutions.

0 10 20 Retention t imehin

30

Fig. 1. Separation of dichlorophenol isomers by a column coated with 20% dibenzo-18-crown-6 on C,, 60-80 mesh at 140 "C. Peaks: 1, solvent; 2, 2,6- dichlorophenol ; 3, 2,5-dichlorophenol; 4, 2,4-dichlorophenol; 5, 2,3-dichloro- phenol ; 6, 3,5-dichlorophenol; and 7, 3,4-dichlorophenol.

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October, 1983 SHORT PAPERS 1267 As shown in Table I, for the separation on polysiloxanes, the greater the phenyl content, the

better is the separation and it is therefore concluded that the phenyl group plays an important role in the separation of dichlorophenol isomers on polysiloxanes. The elution order on silicones KF-54, KF-53, KF-56, KF-50, KF-965, SH-710 and FL-100 is the same as the order of increase in boiling-point (2,5-, 2,4-, 2,3-, 2,6-, 3,5- and 3,4-dichlorophenol) and that on dioctyl phthalate, a Bentone-34 modified with sorbitol or mannitol and crown ethers, is 2,6-, 2,5-, 2,4-, 2,3-, 33-, and 3,4-isomers, which is different from the former elution order.

Conclusion Although it is difficult to analyse dichlorophenol isomers as the free phenol by gas - liquid

For the resolution It is con-

chromatography, their isomers were resolved well on dibenzo-18-crown-6. on polysiloxanes, the elution order followed the order of increase in boiling-point. cluded that phenyl groups present in liquid stationary phases play an important role.

The author thanks Nippon Soda Co. Ltd., Shinetsu Chemical Co. and Torey Silicone Co. Ltd. for kindly supplying the crown ethers, polysiloxanes and silicone SH-7 10, respectively.

1. 2. 3. 4. 5. 6. 7. 8. 9.

10. 11. 12. 13. 14.

References Barry, J. A., Vasishth, R. C., and Shelton, F. J., Anal. Chem., 1962, 34, 67. Kolloff, R. H., Breuklander, L. J., and Barkley, L. B., Anal. Chem., 1963, 35, 1651. Sugi, A., Dan, M., and Fujihara, M., Nippon Daigaku Yakugaku Kenkyu Hokoku, 1963, 5-6, 13. German, I. A., and Ciot, N., Rev. Chim. (Bucharest), 1966, 17, 177; Chem. Abs.fr., 1966, 65:61216. Andrzei, N., Aleksy, P., and Stanislaw, W., Chem. Anal. (Warsaw), 1969, 14, 1115. Ress, J., and Higginbotham, G. P., J . Chromatogr., 1970, 47, 474. Hudzik, M., and Sokolowska, J., Chem. Anal. (Warsaw), 1971, 16, 183. Ono, A., Takase, T., and Komagata, H., Fresenius 2. Anal. Chem., 1982, 313, 533. Harry, D. R., and Norman, R. 0. C., J . Chern. SOG., 1961, 3604. Ono, A. J., Chrornatogr., 1980, 193, 300. Ono, A., Chromatographia, 1980, 13, 574. Ono, A., Chromatographia, 1980, 13, 752. Sassenberg, W,, and Wrabetz, K., Fresenius 2. Anal. Chem., 1961, 179, 333. Sassenberg, W., and Wrabetz, K., Fresenius 2. Anal. Chem., 1961, 184, 423.

Received January 7th, 1983 Accepted M a y 17th. 1983

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