composition of organic sulfur compounds and no concentration step is required. The standard deviation for the spectrotitrntion of sulfate is k 3.2 pg. sulfur \=k 12.6 pg. sulfate) a t the 500 pg. sulfur level. LITERATURE CITED
(1) Aconsky, L., Mori, M., ANAL. CHEM. 27, 1001 (1956). ( 2 ) Agazzi, E. J., Bond, G. W., Ibid., 33, 972 (1961).
(3) Bertolacini, R. J., Barney, J. E., 11, Ibid., 29, 281 (1957). (4) Flaschka. H., Sawver, P., Talanta ‘ 9, 249 (1962). ’ (5) Fritz, J. S., Pietrzyk, D. J., ANAL. CHEM. 31, 1157 (1959). (6) Fritz, J. S., Yamamura, S. S., Ibid., 27, 1461 (1955). ( 7 ) Goddu, R. F., Hume, D. S . , Ibid., 26, 1740 (1954). (8) Headridge, J. B., Talanta 1, 293 (1958). (9) Lindstrom, F., Stephens, B. G., ANAL.CHEM.34,993 (1962). “
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(10) Rinehart, R. W., Stafford, J. E., Microchem. J. VI, 567 (1962). (11) Silverman. H. P.. Skooe. D. A.. ANAL. CHEM:35, 131’(1963);’ (12) Wadelin, C. W., Talanta 10, 97 (1963). (13) Zak, B., Hindman, W. M., Baginski, E. S., ANAL.CHEM.28, 1661 (1956). H. WHITNEY WHARTON L. RICHARD CHAPMAN The Procter & Gamble Co. Miami Valley Laboratories Cincinnati 39, Ohio
Etched Glass Beads as Gas Chromatographic Support SIR: Calculations by Giddings (2, 3) have indicated t h a t the efficiency of glass bead columns should improve if the beads are grooved or roughened before the liquid phase is applied. Although Giddings used the grooved or “sawtooth” model to show the advisability of removing capillary liquid from the bead contact points and redistributing it more evenly around the bead, it is apparent that a n etched or pitted surface should accomplish much the same ends. Dewar and Maier ( I ) found no improvement in column performance when mechanical abrasion was used to roughen the bead surface. Our results with mechanical abrasion substantiate their findings. However, they did find a considerable improvement in column performance when powders such as very fine diatomaceous earth were added to the liquid phase. We have found that etching the beads with dilute gaseous hydrogen fluoride prior to application of the liquid phase leads to more efficient columns.
Beads etched in the above manner showed a very consistent etch-that is, the general appearance of the etch, upon microscopic examination, did not vary much from bead t o bead. hll attempts a t mechanical abrasion or liquid phase etching failed to produce such consistent etches. The exact contours of the etched surface cannot be described, since the dimensions of the width and depth of a pit or groove were submicroscopic (less than 1 micron). However, on the basis of the fact that the columns described below were essentially saturated-Le., addition of liquid above the .25y0 used in this work caused liquid to accumulate between the bead contact points-the depth of etch was calculated at about 0.4 micron. Although only one set of comparative data are given here, the work was repeated with other columns of similar construction with much the same results.
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Column A was prepared with unetched 60- to 70-mesh beads, and column 13 was prepared with etched beads of the same mesh size. Both columns were coated with Dow Corning 200 silirorie oil (100 centistokes at 25’ C.). These columns were prepared to hold 0.25% liquid. Samples were injected as .05 ml. of air saturated with n-nonane (Phillips Research Grade). Both columns were constructed of 25-inch 0.d. brass tubing and were 27.5 cm. long. Column temperature was 40.0’ . l oC., and hydrogen flame ionization was used to detect the eluted peaks. The ratio of zone to gas velocity for column X was .038 and for column E, .035.
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RESULTS A N D DISCUSSION
Microscopic examination and measurement of the coated etched and unetched beads yielded results which
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Column A 0 , ’
Column B.
EXPERIMENTAL
Glass beads (Wilkens Instrument & Research, Inc.) were sifted into a 60t o io-mesh fraction and cleaned with hot Cr(V1) acid solution. These were then etched by suspending them in a rapidly moving column of an airhydrogen fluoride mixture. A polyethylene bottle containing calcium fluoride and concentrated sulfuric acid was used to generate hydrogen fluoride, and air was drawn through the generator and etching column with a wateraspirator pump. A trap packed with shredded filter paper was inserted between generator and etching column to remove sulfuric acid mist. Total time of etching was approximately 2 hours. The etching column was a borosilicate glass tube, 1.7 cm. in diameter and approximately 30 cm. long, and could accommodate approximately 10 ml. of glass beads a t a time. T o help ensure uniformity of column packing, separate batches of beads were not mixed. This precaution necessitated the use of very short chromatographic columns.
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Figure 1 .
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IO Vg’ cm/sec
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HETP for n-nonane as a function of outlet gas velocity 0
Hydrogen corrier gas Nitrogen corrier gas VOL. 36, NO. 8, JULY 1964
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were in excellent agreement with the calculations of Giddings concerning the equilihrium liquid phase configuration. Cnetched beads yielded a value of 30 + 3 microns for the depth of liquid accumulated around the bead c,ontact points, whereas the etched beads had a dry appearance with no measureable amount of liquid at' the bead contact points. These results show that t,he majority of the liquid accumulates around the bead contact points of the unetched beads even a t this low liquid loading. The data given in Figure 1 summarize the performance characteristics of the two columns. Both hydrogen and nitrogen were used as carrier gases so that C Lcould be evaluated according to one of the methods suggested by Purnell (4). L'nfortunately, the data are not sufficiently precise for an accurate determination of the rate equation
parameters. However, on the basis of the available data, C L for column B is approximately one order of magnitude less than C I for column A. This work will be extended to longer columns and (hopefully) more accurate determinations of C Lfor the two types of columns. Despite the increase i n efficiency of the etched bead column, the use of these columns with polar solutes may be attended with difficulty, since the higher specific surface area apparently tends to increase tailing with polar solutes. This conclusion is based on some results using 2,4-pentanedione as solute in the two types of columns. On the other hand, further studies in this area with nonpolar solutes should prove valuable, since a unique opportunity exists to alter the liquid phase configuration in a known manner while keeping all other column parameters constant.
ACKNOWLEDGMENT
The authors thank Timothy Konkol for his suggestion of the etching technique described above. LITERATURE CITED
(1) Dewar, R. A., Maier, T'. E., J . Chromatog. 11, 295 (1963). ( 2 ) Giddings, J. C., AXAL.CHEM.34, 458 i lM21. ( 3 j Zbzd:, 35, 439 (1963).
(4)Purnell, H., "Gas Chromatography," p. 159, M'iley, S e w York, 1962.
R. M'AY~YE OHLINE RAYMOXD JOJOLA Department of Chemistry Sew Mexico Institute of Mining and Technology Socorro, Yew Mexico WORKsupported in part by the Xational Science Foundation under the Undergraduate Research Participation Program,
Removal of Cation Interference in Paper Chromatography of Concentrated Wet-Process Phosphoric Acid SIR: The method of Huhti and Gartaganis (6) for the paper chromatography of concentrated phosphoric acid was applied without difficulty to electric-furnace superphosphoric acid (6), from which it separated nine phosphatic species. .4ttempts to apply the method to acid prepared by concentration of wet-process phosphoric acid, however, were much less successful because of interference of phosphatic complexes of the metallic impurities, largely iron and aluminum, that had been dissolved from the phosphate rock. Methods were sought for removal of the metallic cations wit'hout change in the distribution of the phosphatic species in the acid. The complexes of the trivalent metallic cations with the condensed phosphates were too stable for the cations to be separated quantitatively by cation or anion exchange resins. Chelation of the cations and extraction of the chelates with nonaqueous solvents, however, effected separation of the rations. This method has t'he advantage that the chelation is carried out in neutral or slightly basic conditioils, under which hydrolysis of the vontirnsed phosphate species is minimized. EXPERIMENTAL
Reagents. EDTA\, 1.0%. Dissolve 1 .O gram of disodium (ethylenediriitri1o)tetraaretate dihydrate in 100 ml. of H,O. Acid Solvent. 1 I i s 7 5 ml. of iso!)rollanol, 25 ml. of 20% trichloro1682
ANALYTICAL CHEMISTRY
acetic acid. and 0.3 ml. of SHdOH (28% KHs) ' ( 2 ) . Color-Developing Solution. Dissolve 1.0 gram of ammonium heptamolybdate in 50 ml. of H 2 0 , add 5 ml. of 70% HC10, and 1 ml. of HC1 (37%), and dilute to 100 ml. ( 3 ) . Separation of Cations. Dilute 1 gram of the acid to 50 ml. in a 150-ml. beaker 2 ) ",OH and neutralize with (1 to pH 6, keeping the sample cool. Dissolve 1 gram of S a diethyldithiocarbamate in the solution and wash the solution with ch!oroform into a 100ml. separatory funnel. Shake for 30 seconds, settle, and discard the chloroform layer. Repeat the extraction until the chloroform layer is colorless; one repetition usually is sufficient. Return the aqueous solution to the beaker, add 3 grams of 8-quinolinol, stir 2 minutes with a magnetic stirrer,
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adjust p H to 9 to 10 with (1 2) N H 4 0 H , add 50 ml. of chloroform, and continue stirring for 15 minutes. Transfer to the separatory funnel, allow to settle, and discrtrd the chloroform layer. Return the aqueous solution to the beaker, add 0.5 to 1.0 gram of 8-quinolinol, and repeat the extraction until the chloroform layer is colorless. The number of extractions varies with different acids, but three repetitions usually are sufficient. Filter the aqueous solution through a plug of cotton to remove chloroform and add 5 ml. of the EDTA solution to chelate remaining traces of cations. The solution then can be spotted immediately or stored in a refrigerator for as long as 24 hours. Chromatographic Analysis. At the apex of a filter paper (Schleicher and Schuell No. 589 orange ribbon) cone,
NlDENTlFlED TERFERENC
rp
PHOSPHATE HELD BY CATIONS
U N T R E A T E D ACID
A F T E R REMOVAL OF C A T I O N S
Figure 1 . Chromatograms of concentrated wet-process phosphoric acid
