Table 1.
Ion
Hg(1) Hg(I1)
R, of
Inorganic Ions Using Molten Salt Solvent
R, 0.98 0.94 0.30 0.00 0 .00
Color of s ot with (Nd)&3 black brown brown yellow-brown black
less prone to abrasive damage. This may cause difficulties if one wants to remove a separated fraction. Further experiments are under way t o extend the use of molten salts in thin layer chromatography and to investigate the usefulness of various complexing anions on inorganic separations. ACKNOWLEDGMENT
necessity for a large molten salt bath or a well regulated furnace, this method offers no complications. The solidified solvent on a developed chromatogram gives a resulting plate
The author thanks James Schlegel for the use of his molten salt bath. LITERATURE CITED
(1) Alberti, G., Grassini, G., J . Chromafog. 4, 425 (1960).
(2) Alberti, G., Grassini, G., Trucco, R., J . Elecfroanal. Chem. 3, 283 (1962). (3) Gruen, D. M., Fried, S., Graf, P., McBeth, R. L., Proc. 2nd International Conf. on Peaceful Uses of Atomic Energy, United Nations, Geneva, Vol. 28, p. 112, 1958. (4) Hanneman, W. W., Spencer, C. F., Johnson, J. F., ANAL.CHEM.32, 1386 (1960). ( 5 ) Juvet, R. S., Wnchi, F. M., ASAL. CIIEY. 32, 290 (1960). LEONARD F. DRUDINQ Department of Chemistry Rutgers, The State University Newark 2, N. J. RECEIVEDfor review June 24, 1963. Accepted July 22, 1963. Research was assisted by a grant from the University Research Council.
Preparation of Thin-Film Gas Chromatographic CoIumns with Polyvi ny IpyrroIido ne-Inac tiva ted S u ppo rts SIR: Gas chromatographic columns used for analytical purposes with steroids and other polyfunctional compounds of comparable molecular size and structural complexity are best prepared with inactivated supports. Various silanizing procedures for the deactivation of diatoniaceous earth supports have been published [see (3,4) and references cited therein], but the separation of hydroxyl-substituted compounds without partial adsorption and tailing is often difficult even when a silanizing procedure is used. The extent t o which tailing may occur depends upon both the structure of the solute and the nature of the support and the phase. I n a continuing search for ways of preparing superior thin-fdm columns with
polar phases, the possibility of deactivating supports by a coating process using an organic polymer was considered. I n pursuit of this possibility, it was found that polyvinylpyrrolidone (PVP) did not itself function as a satisfactory liquid phase at 200' to 220' C., but t h a t supports coated with 1 to 2% P V P could in turn be coated with a liquid phase to yield a n excellent column packing. The column used to obtain chromatogram B of Figure 1 was prepared with a thin-film packing containing 1% neopentyl glycol succinate (KGS) on an acid-washed (3) diatomaceous earth support (Gas Chrom P) coated with 1% P V P before the polyester film was applied. The slurry coating technique of Horning, Mos-
A NGS SILPNIZED
B 1 %NGS WP
Figure 1. Gas chromatographic separation of mixture of cholesteryl acetate (CeAc) and cholesterol (CeOH) with 1 % NGS on differenily inactivated supports (A, silanized; 5, PVP-treated)
catelli, and Sweeley (2) was used both
for the I'VP coat (methanol solution) a,nd the KGS (acetone solution) coat. For coinparison, the result obtained with a packing containing 1% NGS on a n acid-washed and silanized support (3) is shown in Figure 1A. In separate experiments it was found that PVP-treated supports were not suitable for the preparation of thin-film packings with nonpolar silicone polymers. This may be due to poor wetting of the polar PVP surface by these Table 1. Comparison of Effects Found With a Silanized Support and a PVPInactivated Support
Relative retention time 1%N G P 1% Silanized PVP
Compound Cholestane 1.OOb 1 .O@ Cholestanyl methyl ether 2.i5 2.78 i-Cholesteryl methyl ether 1.27 1.30 Cholestenol 6.59 i.87 8.42 Cholesterol 7 11 Cholestane-3-one 7.16 7.22 Chalesteryl acetate 6.37 6.32 Androstane-3,9.1ip-diol 5.24 9.51 Pregnane-3a,20a-diol 7.19 11.3 Androstane-3,17-dione 5 43 6.08 6.i 0 7.27 Pregnane-3,20-dione 8.04 L~-Pregnane-3,20-dione7 . 3 7 0 Both columns i6-ft. X 4-mm. i.d. glase U-tubes) were operated in same column oven with same detector (argon ionization) and conditions (216' C., 100 ml./min.). The support (100-120-mesh Gas Chrom P) was acid-washed (3). One portion was then silanired and coated according to (3); the other portion was coated with lY0 PVP before application of the polyester. b Cholestane time, 4.4 min. Cholestane time, 4.6 min. 0
Column conditions given in Table I
VOL 35, NO. 11, OCTOBER 1963
1745
4
3.30 - 1
2.90
2.10
Figure 2. Variation of response ratio (ratio of peak areas) of cholestanol-tetratriacontane mixture with sample size (micrograms of cholestanol) with two differently prepared column packings (A, PVP-treated; 6, silanized)
1
Column conditions given in Table I
retention behavior found for steroids with hydroxyl groups. Alcohols were retained much longer than the corresponding ketones. It is not certain if the changed selective retention behavior of the solute is due to interaction with the PVP surface beneath the film of NGS or results from a partial solution of PT‘P in the polyester phase.
1
01
LITERATURE CITED I
I
I
2
I
I
I
I
3
4
5
6
MICROGRAMS
materials. However, polar phases could be coated on PVP-inactivated supports without difficulty. Columns made with these packings showed several interesting properties. The almost complete absence of tailing seen with a sterol is illustrated in chromatogram B of Figure 1; the shape of the peak suggests that adsorption of the sterol is less than t h a t found when a silanized support is used. This was confirmed by a study using the approach of Horning et al. (1). Figure 2 shows the variation of response ratio (ratio of peak areas) of a
cholestanol-tetratriacontane i n i ~ t u r e with sample size for two types of columns. The superiority of the PPPcoated packing with respect to lack of adsorption is evident. Table I contains relative retention time data comparing effects found with a silanized (with dichlorodimethylsilane) support and a PVP-inactivated support. Since the retention times observed for a number of steroids are about the same under the two conditions, it appears that P V P is not itself acting as a liquid phase. Kevertheless, P V P coating modified the
(1) Horning, E. C., Maddock, K. C., Anthony, K. V., Vanden Heuvel, IF’. J. A., ANAL.CHEW.35,526 (1963).
(2) Horning, E. C., Moscatelli, E., Sweeley, C. C., Chem. Ind. London 1959, 751. (3) Horning, E. C., Vanden Heuvel, W.J. A., Creech, B. G., in Glick, D., “Methods of Biochemical Analysis,” Vol. XI, Interscience, Xew York, 1963. (4) Ottenstein, D. M., J . Gas Chromatog. 1, KO 4,11(1963). W. J. A. TIASDEN HECVEI. W. L. GARDIXER E. C. HORNING Lipid Research Center Baylor University College of lledicine Texas Medical Center Houston, Texas RECEIVEDfor review N a y 20, 1963. Accepted August 20, 1963. Work supported by Grant HE-05435 from the Xational Institutes of Health.
Vanadium(II)-1 ,I 0-Phenanthroline as an Oxidation- Reduc ti o n Ind icato r SIR: Vanadium in its +Z, +3, and +4 oxidation states forms complexes with 1,lO-phenanthroline ( I ) , but no complete description of any of these systems has been published. The review article quoted (1) describes the vanadium(I1) complex ab being intensely blue-violet. During a systematic study of all of the vanadium-1,lOphenanthroline complexes, the possibility of using this intensely colored compound as an oxidation-I eduction indicator was explored. I n dilute acid solution the color is bleached by oxidizing agents a t about 0.0 volt us. S.C.E.; the color is restored by chromous ion at about -0.1 volt us. S.C.E. It is RS a n indicator for titration with strong reducing agents such as Cr(l1) that this complex may be useful. Chromous chloride and chromous sulfate are ~ e l establ lished as reducing agents (8,4 ) but are 1746
ANALYTICAL CHEMISTRY
generally used with potentiometric end point detection; the green color of the chromic ions produced when Cr(I1) is oxidized tends to obscure a visual end point. Some organic indicators which have transition potentials near 0.0 volt us. S.C.E. have been described, but many of them are insoluble, unstable, or otherwise unsuitable ( 3 ) . This communication describes the use of the vanadium(I1) complex with 1.10-phenanthroline as an indicator in titrations with chromous ion; the details of the formulas and stability of the species involved are being investigated. The esact nature of the colored species is not particularly relevant to this type of npplication because equilibrium between V(I1) and 1,lO-phenanthroline is very slowly attained; a sufficient color intensity is developed in 2 to 3 seconds, however, to serve as a titration indicator.
A solution of s’(I1) and 1,lO-phenaathroline (1:4) in 0.01F HCl shows a broad absorption band with a maximum at 645 mp. The molar absorptivity is 5400 liters per mole-em. (calculated for the vanadium) when the solution is fresh and it increases to over 8000 in 36 hours. The colored complex formed by the reduction of vanadyl ion v i t h Cr(I1) in the presence of 1 , l O phenanthroline has the same spectrum as the T‘(II) preparation. The indicator is prepared from T’OCI2 2nd 1,lO-phenanthroline. Take 0.228 gram (1.25 mmoles) of V206and heat it briefly in 10 ml. of 3F HC1. Cool to room temperature, add 0.25 gram of Na2S03. and heat gently until all the VZOshas been converted to VOClz and the excess SO? driven off. Dilute to 50 ml., add 1.49 grams (7.50 mmoles) of 1,lO-phenanthroline monohydrate, and
