1578
ANALYTICAL CHEMISTRY, VOL. 50, NO. 11, SEPTEMBER 1978
__
4 CG
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7
,
3cc-
J
:
J"
T
cc
i
2 YCH -~
. ' 1 -
i _
_
_ _- ~
C
2 5
5
nc
L 3 0 h
-~~ -4
--
-L
~
--2 2c
~
ti
Figure 1. Effect of added NaOH on the phosphorescence half-lives
E. M. Schulman and C. Walling, J . Phys. Chem., 77, 902 (1973). E. M. Schulman and R. T. Parker, J . Phys. Chem., 81, 1932 (1977). E. Wiedemann and G. C. Schmidt, Ann. Phys. 5 6 , 16, 201 (1895). E. Tiede and P. Wulf, Berichte, 55, 588 (1922). G. N. Lewis, D. Llpkin, and T. T. Magel, J . Am. Chem. Soc.. 63, 3005 (1941). G. N. Lewis and M. Kasha, J . Am. Chem. Soc., 66, 2100 (1944). R. A . Paynter, S.L. Weiions, and J. D. Winefordner, Anal. Chem.. 46, 736 (1974). S. L. Wellons, R. A. Paynter, and J. D. Winefordner, Spectrochim. Acta, Part A , 30, 2133 (1974). P. G. Seyboid and W. White, Anal. Chem., 47, 1199 (1975). R. M. A . von Wandruszka and R. J. Hurturbise, Anal. Chem.. 48, 1784 (1976). T. V*Dinh, G. L. Walden, and J. D. Winefordner, Anal. Chem., 49, 1126 (1977). P. G. Seybdd and F. Fanis, unpublished results, Unkersky of Illinois, Urbana, Ill., 1970. P. G. SeyboM, R. K. Sorrell, and R. A. Schuffert, Abstracts, 165th Nationai Meeting of the American Chemical Society, Dallas, Texas, 1973. W. White and P. G. Seybold, J . Phys. Chem., 81, 2035 (1977). J. L. Charlton and B. R. Henry, J . Chem. Educ., 51, 753 (1974). S. P. McGiynn, M. J. Reynolds, G. W. Daigre, and N. D. Christodoyleas, J . Phys. Chem., 66, 2499 (1962).
of 2-naphthalenesulfonate,2-naphthoic acid, and 2-naphthol adsorbed on filter paper
ACKNOWLEDGMENT We are grateful to William Feld and the late Robert Breeze for their help in constructing the lifetime apparatus. We also thank Edward Schulman for very helpful discussions of this topic.
LITERATURE CITED (1) M Roth, J Chromatogr 30, 276 (1967) (2) E M Schulman and C Walling, Science, 178, 53 (1972)
Gary J. Niday Paul G. Seybold' Department of Chemistry Wright State University Dayton, Ohio 45435
RECEIVED for review November 10, 1977. Accepted June 22, 1978. Acknowledgement is made to the Donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research.
Surface Treatment for Chromatographic Packings: Attachment of Tetrachloroterephthaloyl Half Esters Sir: In the course of our investigation on the applications of tetrachloroterephthaloyl aromatic nuclei in chromatography (1,2),we have found it possible to attach the half esters such as tetrachloroterephthaloyl heptafluorobutyrate (I) to silica surfaces, presumably with the predominant structure (IIa) to give a new type of surface bonded chromatographic packing (3, 4 ) . I 0
0
Cl
CI
CI
CI
-0 -;,-O-!+m
I
0 I
/I
0
(11)
(a) R
=
-CH,CF,CF,CF,; ( b ) R
=
-CH,CH,CH,
EXPERIMENTAL The stationary phase packing was prepared by reacting 150 "C pre-dried, 80-100 mesh Porasil C (50-100 m2/g surface area, 200-400 Angstrom pores) with heptafluorobutyl tetrachloroterephthaloyl chloride (4-carboheptafluorobutoxy-2,3,5,6-tetrachlorobenzoyl chloride), mp 88-90 "C, and N-methyl-piperidine in heptane at 50 "C for a week. The treated Porasil was filtered, rinsed with acetonitrile, benzene and hexane, and dried under nitrogen. While they are not quantitatively accurate, microanalyses confirmed the presence of carbon, fluorine, and chlorine on the silica surface. The qualitative, well known "water floating" test which can be used to establish the hydrophobic nature of the support surface was used for the beads treated above. About three quarters of the beads were found to float on water for the duration of the test (about 3 h) presumably because of structures similar 0003-2700/76/0350-1576$01 .OO/O
to IIa. The treated beads seemed t o be reasonably resistant to solvolysis; they retained their water resistant character even after 12 h of soaking with propanol-water mixtures in the range of 10-90% propanol. The surface modified material was packed in a 3-mm 0.d. 120-cm column (1.543 g) and tested in a Carle Basic 8000 Chromatograph. Porasil C also was reacted with propyl tetrachloroterephthaloyl chloride, mp 74-75 "C, in a manner similar t o the treatment above to give IIb, and tested in a column. A third column with Porasil C was treated in situ with Silyl8 (Pierce Chemical Co., Rockford, Ill.), a reagent for surface trimethylsilylation for comparison. The Silyl 8 treatment consisted of twenty-four 6-pL injections at 80 O C when no further change took place in the surEace as evidenced by chromatography. A fourth column was packed with Durapak, a commercial packing (Pierce Chemical Company) for further comparison. This material is reported to contain octyl groups attached directly to the surface silicon atoms of Porasil C. A fifth column with untreated Porasil C was also tested.
RESULTS AND DISCUSSION T h e new treatment reported here imparts surface characteristics differing from both silanized Porasil and untreated material, and somewhat dependent on the surface ester group. I n Table I, relative retention volumes of representative compounds on the packings studied here are shown a t 85 "C. Representative capacity factors ( k ' values) for IIA and IIB-Porasil C are shown in the footnotes of Table I. Figure 1 shows a chromatogram from the column packed with Porasil C treated to give the surface resembling IIa. Chromatograms from untreated Porasil C were useless for meaningful comparison because of severe tailing. As predicted by the data C 1978 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 50, NO. 11, SEPTEMBER 1 9 7 8
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Table I. Relative Retention on Surface Modified Packings toluene = 1, T = 85 ’C
-___---
--__
trimethylsilylatecl Porasil C
IIA-Porasil C
IIB-Porasil C
0.55
0.102
0.95 1.62 2.79 0.56 0.84 0.57
0.214
0.062 0.127 0.260f 0.535 0.064
0.12 0.25 0.53 0.25 0.39
10
l b
0.115 0.380 1”
1.61 1.86 1.86 1.96 0.45
2. 04g
hexane heptane octane nonane cyclohexane methylcycloht 2xane benzene toluene ethylbenzene m-xylene p-xylene o-xylene chloroforni
0.447e
0.94 0.106 0.176 0.41 2.26 2.33 2.61 0.27
n-octane-Porasil C Durapa k
1.93h 2.59 2.50 2.68 0.157
1.14 0.14 Id
-
2.59 2.50
-
0.19
Corrected retention volume per gram: ( a ) 6.4 cm’/g; ( b ) 1 4 3 cm3/g;( c ) 1 4 7 cm3/g;( d ) 88 cm’/y. Capacity factors ( k ’ values): (e) 20.3; ( f ) 21.0; (g) 92.5; ( h ) 143.0. _ _ . ~ I _ _ _ _
-
0
~
IO
~. ~~~~
Ti---. ~~
20 35
~
~
_ _ _ _ _ I I
-~ ~
~~~~~
45 (rnin)
55
Flgure 1. Chromatographic separation of hydrocarbon mixture on Porasil C-Ha, 80-100 mesh; 1 2 0 cm X 0.22 cm i.d. aluminum column; T = 8 1 O C , corrected flow = 9.3 cm3/min of He, AP =: 7 8 1 mm Hg; 6 pL of vapor. (A) Air, (B) cyclohexane, (C)rnethylqclohexane,(D) chloroform ( E ) benzene, (F) toluene (G) ethylbenzene, (H) p-xylene, (I) o-xylene
of Table I, the nonselective nature of the trimethylsilylated surfaces is demonstrated by the failure to separate cyclohexane and benzene. The illustrative chromatogram of Figure 1 shows t h a t the new packing can perform this separation quite satisfactorily. Treatments to prepare IIA-Porasil C were duplicated and found to give columns which were essentially chromatographically reproducible. T h e data on Table I further illustrate the selective separation of alkanes from aromatics, octane being eluted before benzene for IIb and heptane before benzene for IIa. Cyclohexane is easily separated from benzene. While there are solid packings available with similar or greater selectivity for aromatics (5),they often are not sensitive to aromatic isomer differences. T h e variation in specificity for aromatic isomers for the treatments described here is illustrated in the Table with p - to n-xylene retentions. The order of elution is actually reversed for IIa compared to other phases with the para isomer retained. The inversion of the para-meta xylene elution order, counter to their vapor pressures as well as aromatic retention, is probably due to selective ‘‘T-T’*charge transfer interaction between t h e aromatic hydrocarbon solutes and t h e electronegatively substituted tetrachloroterephthaloyl aromatic nucleus ( I , 2 ) . While the separation change brought about by attachment of t h e tetrachloroterephthaloyl half ester to the surface does not give a separation factor adequate for the para-meta xylene separation, the situation might be more favorable with the addition of a very small amount of a suitable bulk stationary phase (6) such as a suitable tetra.chlorophthalate ( 2 ) or a liquid crystal liquid phase (7). T h e change in meta--para xylene elution order for IIb in comparison with IIa is probably associated with the alkyl ester group of the former as well as steric effects from the close attachment of the tetrachloroterephthaloyl nucleus to the silica
__
surface which may impede selective
