670
ANALYTICAL CHEMISTRY
ground-glass cap may be added to the sample flask to facilitate the addition of solvent. When the method is employed for materials of low sulfur percentage-i.e., 0.1% sulfur-the standard A.S.T.M. sample flask mav be enlarged to enable a 30- to 40-ml. solution of the sample to be burnedFor very low percentages of sulfur, a microprecipitation and filtration procedure may be applied to the absorption solution. The results of the combustion of samples containing elemental sulfur indicate that this modification may offer a solution to previous difficulties (1,4 ) with the determination of total sulfur in the presence of free sulfur. Data illustrating precision and accuracy obtainable with the
present lamp method are given in Table I. (Cotton wicks were used in these determinations.) LITERATURE CITED
(11 Altieri, V. J., “Gas Chemist’s Book of Standards for Light Oils and Light Oil Products,” 1st ed., pp. 119-24, New York, American Gas Association. 1943. (2) Am. Soc. Testing Materials, “Standards on Petroleum Products and Lubricants,” pp. 706-12, Designation D 9047T, 1949. cHEM., ANAL. ED., 17, 642-5 (3) Hinc&y, J. A., J~.,et al., (1945). (4) Lane, W. H., ASAL. CHEX, 20, 1045-8 (1948). R E C E I ~ EAugust ~
22, igrjo.
Talc as an Adsorbent for Sulfonated Azo Dyestuffs ROBERTA M. HANSON AND C. W. GOULD General Aniline and Film Corp., Easton, Pa.
REVIOUS chromatographic separations of water-soluble Yacid dyes (mostly azos) were carried out by Ruggli and Jensen (8, 9),who used alumina or alumina activated by prewashing with lime water. These adsorbents were effective in separating dyes nlhich contained different numbers of azo linkages, hut were not shown to be generally useful in separating isomers or closely related derivatives. These authors also tested talc, silicic acid, calcium hydroxide, and calcium carbonate as adsorbents without encouraging results. Wykspiel (II), in his review of the subject up to 1940, concluded that alumina is by no means a universal adsorbent: Some acid dyes are retained in a tight immovable zone a t the top of the column, while others pass rapidly into the filtrate. Karabinos and Hyde ( 1 )reportrd the chromatography of some common indicators, including Congo red and methyl orange, using Silene E F as adsorbent and solutions in 90% dioxane-10% water. Strain (IO)separated some acid dyestuffs in aqueous solution by a combination of chromatographic adsorption and electrophoresis. The columns were packed with Hyflo Super-Cel, cotton, or talc-Super-Cel mixtures. Electrodes a t the top and bottom of the column (potential difference 175 to 200 volts) caused migration of dyes drawn into the top of the column. In the authors’ hands the above procedure gave unsatisfactory results with a mixture of three monoazo dyes. Nearly inert column packings such as Hyflo Super-Cel, powdered glass, and glass wool gave poor separations, as did a mixture of alumina (powdered Hydralo) and Super-Cel. However, with talc-powdered glass or talc-Super-Cel excellent separations were observed with or without potential applied to the electrodes. Without the electrophoretic effect a more distinct chromatogram resulted. Potential applied to the electrodes did not change the order of zones on the column, but did cause widening of some of the zones. It is probable that in the test substances the electrophoretic mobilities for some components were not in the same order as their chromatographic migration rates. These experiments led to a study of the effectiveness of talc aa a chromatographic adsorbent. The results are summarized in Table I. DEVELOPMENT OF TALC CHROMATOGRAMS
In the usual procedure, the dyes were dissolved in water, adsorhed on a column of talcSuper-Cel, and caused to migrate by development with dilute solutions of pyridine (0 to 10%) in water. A mixture of Congo Corinth
OH
”2
and Congo red SH*
NH,
shoued an interesting reversal in zone order as the pyridine concentration in the developer was increased. Without pyridine no separation was observed. With 5% pyridine a fair separation took place with Congo Corinth below Congo red on the column. With 10% pyridine, a reversal of order and excellent separation were obtained, with Congo red below Congo Corinth and separated from it by a n4de colorless zone. Increasing the pyridine concentration to 20% gavcx the same zone order but blurred the separation. In experiments with other alkaline developing agents, sodium carbonate (0.15 to 1.5 $1) and sodium hydroxide (0.5 to 5 31) apparently salted out the dyes a t the top of the column and allowed no migration. With concentrated ammonia the mixture was slowly separated; in this case Congo red wm more strongly adsorbed than Congo Corinth. Prewashing the column with 5 ikf sodium hydroxide, followed by adsorption and development with 10% aqueous pyridine, led to a complete separation with Congo red tightly held a t the top of the column while Congo Corinth moved rapidly into the filtrate. Without the prewashing, the order was reversed. Table I is a summary of the adsorption behavior for some pairs of similar dyestuffs, arranged in groups according to the number of azo linkages. With each structure is the Colour Index ( 7 ) number. An asterisk before the number indicatea that the dyestuff was freed of inorganic salts before testing. In all cases there was a colorless zone between the zones containing major components corresponding to the structures given. In the trisazo section of Table I the authors had intended to include some green and brown dyestuffs. But on chromatography of C.I. 583 a t least four colored zones were obtained, in addition to the major green component.
V O L U M E 23, NO. 4, A P R I L 1 9 5 1
671 .. . .
Table I.
..
Adsorption Behavior of Similar Dyestuffs Lower Zone
Upper Zone
.Monoazo Dyes
0 €1
011
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oi ,~ ‘CHI ‘161
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s
=
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