ANALYTICAL CHEMISTRY
1874
oxidation conditions such that both components are differentially oxidized, preferably to specific oxidation levels, is still to be determined. LITERATURE CITED
(1) Adams, Roger, editor, “Organic Reactions,” T’ol. 11, Chap. 8 . Kew York, John Wiley & Sons, 1944. (2) Allen, N., Charbonnier, H. Y., and Coleman, R. M., IND. ENG. CHEM.,ANAL.ED., 12, 384--6 (1940). (3) Rerl, E., and Innes, A. G., Beis deut. chem. Ges., 42, 1305-9 (1909). (4) Birtwell, C., and Ridge, B. P., J . Textile Inst., T r a n s . , 19,341-8 (1928). (5) Cardone, M. J., and Comgton, ,J. IF’., ANAL.CHEM.,24, 1903-8 (1952). (6) Cohen, RI., and Westheimer, F. H., J . A m . Chem. Sac., 74, 4387 91 (1952). (7) Conant, J. B., and Luts, R. E., Ibid., 45, 1047 (1923). (8) Christensen, B. E., Williams, R. J., and King, A. E., Ibid., 59, 293 (1937). (9) Elkins, H. B., Storlazzi, E. D., and Hammond, J. W., J . Ind. Hug. T o ~ i c o l .24,229-32 , (1942).
(10) Francis, C. V., ANAL.CHEM.,21, 1238-9 (1949). (11) Gilman, Henry, editor, “Organic Chemistry, An Advanced Treatise,” 2nd ed., Vol. I, Chap. 1, pp. 56, 60, New York, John Riley & Sons, 1943. (12) Hansen, K., Biochem. Z . , 167, 58-65 (1926). (13) Houghton, 9.A., Analyst, 70, 118-24 (1945). (14) Kolthoff, I. M.,and Laitinen, H. rl.,“pH and Electro Titrations,” 2nd ed., p. 66, New York, John Wiley & Sons, 1941. (15) Kolthoff, I. AT,, and Stenger, V. A , , “Volumetric Analysis,” 2nd ed., Vol. I, pp. 74-6, Xew York, Interscience Publishers, 1942. (16) Lejeune. G., Conipt. rend., 182,694-6 (1926). (17) Lejeune, G., J . chim. phys., 24, 391-426 (1927). (18) AIohlman, F. E’., and Edwards, G . P., IXD.EXG.C H E i r . , A N . ~ I , . ED., 3, 119-23 (1931). (19) Shaw, J . A . , ANAL.CHEM.,23, 1764-7 (1951). (20) Snethlage. H. C. S., Rec. trao. chint., 54, 651-6 (1935). (21) Werner, H. W.,and 1Iitchel1, J . I,., ISD. EKG.CHEX..bar,. ED., 15, 375-6 (1943). RECEIVED for review M a y 6 , 1953. Accepted September 28, 1953. Presented before the Pittsburgh Conference on Analytical Chemistry and Applied Spect r o s c o p y , Pittsburgh, P a . , 1953.
Chromatographic Separation of Glycols and Monohydric Alcohols STEPHEN DAL NOGARE Polychemicals Department, Experimental Station, E . I . du Pont de Nemours & Co., Inc., Wilmington, Del.
A rapid separation procedure was required for analyzing decigram quantities of glycol mixtures and alcohol mixtures. Distillation procedures for effecting these separations required large samples and were not applicable to all glycol mixtures. The current work was undertaken to modify a procedure for the separation of alcohols by partition chromatography and to extend this technique to the separation of glycols. The separations were performed on silicic acid and silicic acid-Celite columns. In both cases theimmobile phase was water; the alcohols were resolved with mixtures of carbon tetrachloride and chloroform, the glycols with butanol and chloroform. The procedures were found suitable for the separation of mixtures of Ci to Cb normal alcohols and the CI to Cc glycols. Isoalcohols were not distinguished from the normal alcohols, and only those glycols containing vicinal hydroxyl groups could be measured. In general, the separations were well defined and gave recoveries of 90 to 110%.
R
APID and accurate methods have not been available for the separation of mixtures of either monohydric alcohols or glycols. Although precision distillation is often employed for such separations, this exacting technique requires relatively large amounts of material. I n the case of certain glycols, the vapor pressure relationships are such that efficient resolution of mixtures is difficult if not impossible. The procedures developed in this laboratory employ partition chromatography for the quantitative separation of the lower monohydric alcohols and also the lower glycols. These methods are an extension of the recent work by Neish (3, 4),who reported the analysis of 2- to 3-mg. quantities of alcohol and glycol mixtures by partition chromatography on Celitewater columns. Upon repeating Neish’s work it was found that preparation of suitable Celite columns was difficult even with the greatest care. Also, the procedure was applicable only to small samples and in this laboratory gave variable recoveries when tested with known alcohol mixtures. I n this investigation separation procedures were developed for mixtures of the lower alcohols and glycols on silicic acid and silicic acid-Celite columns containing water B J ~the immobile aqueous phase. Carbon tetrachloride-chloroform and chloroform-nbutyl alcohol, respectively, were used as developing solvents. Contrary to expectations, only small amounts of the various hy-
droxy compounds studied were irreversibly retained on these supports. APPARATUS
Chromatographic apparatus, the assembly shown in Figure 1, is used to carry out the separations of alcohol mixtures and glycol mixtures. Except for some modifications, this equipment is that described by Marvel and Rands ( 2 ) . The head assembly is designed to permit adsorbent packing and continuous operation under air or nitrogen pressure. B y mani ulation of appropriate stopcocks, different solvents may be adfed successively to the head reservoir without interruption of flow through the column. Both reservoirs are large enough to permit addition of the necessary volume of a given solvent a t one time. A spherical joint connects the column to the head assembly and simplifies packing and cleaning. A manometer near the pressure inlet and a stopcock a t the bottom of the column permit close control of the flow rate. REAGENTS
Silicic acid, Mallinckrodt’s chromatographic grade (100 mesh), analytical reagent. Carbon tetrachloride, analytical reagent, extracted once with an equal volume of water before use. Chloroform, analytical reagent. This material contains ethyl alcohol as a preservative, which is removed by extracting five times with an equal volume of water. Washed chloroform IS unstable and should be prepared as needed.
1875
V O L U M E 25, NO, 12, D E C E M B E R 1 9 5 3 n-Butyl alcohol, analytical reagent. Free acids in this material are removed by simple distillation from sodium carbonate. Sodium metaperiodate (NaI04), analytical reagent, 0.05151 aqueous solution. Sodium hydroxide, 0.05-Yaqueous solution, standardized. Potassium dichromate, 0.04N in 18N sulfuric acid solution. Sodium thiosulfate, 0.02N aaueous solution, standardized. Starch indicator solution, 1%-aqueous solution. Alizarin Yellow R indicator solution, 0.27, in 507; aqueous ethyl solution. Ice, crushed and n-ashed.
Table I.
Equivalents
of Dichromate per RIoleclllar
Weight 32.0 46.1
Alcohol Methyl Ethyl
Equi\alrnt \$-eight
hIole of .4lcohol
60.1
ti-Propyl Isopropyl n B u t yl
60.1 74.1 74.1 88.2 303.2
~
Icohiityl u-.iniyl tt-Ilexyl
PROCEDURE FOR SIONOHYDRIC ALCOHOL MIXTURES
Separation. To 20 grams of silicic acid in a 250-ml. beaker are added 12.5 ml. of water. The mixture is st'irred until it appears homogeneous. Approximately 80 ml. of carbon tetrachloride are added, and the mixture is stirred until a smooth slurry results. RIore or less than the 12.5 ml. of mater may be required to produce a smooth slurry. The correct volume is determined by trial. A cotton pledget is placed in the constriction of the apparatus and the adsorbent slurry poured into the tube. Enough pressure is applied to give a rapid flow rate. The column should be tapped frequently during this operation to ensure uniform settling of the adsorbent,.
Oxidation Equivalents of Monohydric Alcohols by Dichromate Oxidation
T
re
6 a
I
2
1
4
3
6
7
I
D
0
,I
12 :1 84 15 I I I I C I I O U *o
86
1,
18
80
20 21
iz
2,
2'15
PlSl
Figure 2. Separation of C1 to Cg Monohy-dric Alcohols by Partition Chromatography
Figure 1. Partition Chromatography Apparatus
When the top of the adsorbent column is almost dry the lower stopcock is closed, and 50 ml. of carbon tetrachloride are added. The solvent is percolated through the adsorbent a t a fast rate. Care should be taken not to disturb the surface of the column when the solvont is added. When the last of the carbon tetrachloride just enters the top of the column, the lower stopcock is closed and the pressure released. A satisfactory column results when no cracks or voids are visible and the top of the adsorbent column appears firm. The head assembly is removed, and a circle of filter paper is placed on the column. Bn accurately known weight of the alcohol mixture (about 100 mg.) in 1 to 2 ml. of carbon tetrachloride is pipetted onto the column. The sample solution is allowed to enter the adsorbent by gravity. The sample is washed into the column by the successive addition of two 2-ml. portions of the solvent. When the last wash has just entered the column the lower stopcock is closed, the head assembly attached to the column and the alcohols eluted with the following sequence of solvents: 100 ml. of carbon tetrachloride 100 ml. of 1 t,o 3 chloroform-carbon tetrachloride 100 ml. of 1 to 1 chloroform-carbon tetrachloride 175 ml. of chloroform 200 ml. of 1 to 9 acetic acid-chloroform
Each of the solvents (except the last) is shaken with an equal
volume of distilled uTater before use. A flow rate of 2 to 3 ml. per minute is maintained using air or nitrogen pressure. Each succeeding solvent is added when about 10 ml. of the preceding solvent are left on the column. The percolate is collected in 25-ml. volumes and transferred to 125-m1. Erlenmeyer flasks. Each is analyzed for its alcohol content by dichromate oxidation. Analysis of Fractions. To each of the 25-ml. percolate fractions are added 10 ml., or some multiple of this volume, of the 0.04N dichromate reagent from a pipet. As much as 40 ml. of the reagent may be needed to provide an excess if a fraction contains 15 to 20 mg. of an alcohol. S n excess of dichromate is present if a yellow-green color persists in the aqueous layer. The mixture is allowed to stand for 25 minutes with occasional swirling. About 100 ml. of water and 2 to 3 grams of potassium iodide are added. The solution is vigorously swirled and allowed to stand for 5 minutes, after which it is titrated with 0.02.l' thiosulfate to the usual starch end point. The highest nearly constant titration value or the appropriate inultiple of it is taken as the blank from which all other values are subtracted. A plot of the net titration values against fraction number should closely approximate Figure 2 . The amount of each alcohol present in the original sample is calculated from the dichromate oxidation equivalent of the alcohol corresponding to a given percolate fraction. The alcohol content of a given fraction is calculated using the equivalent weights given in Table I. Alcohol mg. = (thiosulfate for blank ml. - thiosulfate for sample, ml.) X normality of thiosulfate X eq. wt. of alcohol. PROCEDUREFORGLYCOLMIXTURES
Separation. The adsorbent is repared by thoroughly mixing 15 grams of a 1 to 2 mixture of &lite-silicic acid with 9.5 ml. of water which has been saturated with 1 to 4 n-butyl alcohol in chloroform. As in the alcohol separation, the resulting mixture is worked into a smooth slurry xith 80 ml. of chloroform and packed into the column under pressure. An additional 50 ml. of chloroform are forced through the adsorbent to complete the packing. Two milliliters of 1 to 4 n-butyl alcohol in chloroform, containing about 200 mg. of the glycol mixture accurately weighed, are pipetted onto the column. When the sample has just entered the adsorbent, two 2-ml. portions of the same solvent are added to wash the sample into the column. Elution of the glycols is carried out with the following order of solvents:
ANALYTICAL CHEMISTRY
1876
between n-butj 1 and isobutyl alcohols. In each case both alcoholsappeared in the 4 same fractions as the normal alcohols. Added, Rec., mg. so Mixtures of n-hexyl and n-amyl alcohols could not be adequately separated by the recommended procedure. Some 20 9 100 9 resolution was obtained with petroleum 20 7 94.7 ether as solvent, but thechromatographic peaks were not distinct. In view of these results the procedure in its present form is suited only to the separation of the CI to C5alcohols without distinction between isomers. Some analyses of known mixtures are reported in Table 11. In all cases the alcohols were the best obtainable commercially. The recoveries from a number of separations similar to those in Table I1 ranged from 83 to 111%. Methyl alcohol generally gave the lowest recovery, possibly because of some irreversible adsorption on the silicic acid. This recovery range could be improved by combining all fractions for a single alcohol (or glycol) and performing only one analysis rather than the three to seven separate analyses as in the present procedure. Upon applying the alcohol separation procedure to mixtures of glycols it became evident that these compounds were much more strongly retained in the immobile aqueous phase than the simple alcohols. Consequently a solvent sequence of greater polarity was required. Solutions of n-butyl alcohol in chloroform, similar to those used to separate dibasic acids ( 2 ) , were most effective. The high proportion of butyl alcohol in these developing solvents resulted in greatly decreased flow rates through the silicic acid-water columns. This difficulty v a s obviated by the use of 1 to 2 mixtures of Celite and silicic acid n hich permitted excellent throughput without use of pressure. The degree of separation achieved by the recommended procedure is shown in Figure 3. I n this case the mixture consisted of 10 nig. each of 1,2-butylene, glycol (l,a-butanediol), 2,3-butylene glycol (2,3-butanediol), and 1,2-propylene glycol (1,2-propanediol) with 170 mg. of ethylene glycol. This mixture and those shown in Table I11 were prepared to simulate impure samples of ethylene glycol; therefore this glycol was not collected. 1,2-Butylene glycol was eluted with 1 to 3 n-butyl alcohol in chloroform, 2,3-butylene glycol and 1,2-propylene glycol were removed with 1 to 1 n-butyl alcohol in chloroform, and ethylene glycol could be completely eluted with n-butyl alcohol. Results obtained with three known mixtures are shown in Table 111. In each case approximately 200 mg. of the mixture were analyzed. The analytical procedure used for the analysis of the chromatographic fractions is that of Dal Nogare and Oemler ( I ) . This method employs periodate cleavage of vicinal hydroxyl groups and is specific for glycols which have hydroxyl groups on adjarent carbons. Consequently only glycols containing this grouping were studied in this work.
Table 11. Analysis of Known Alcohol Mixtures by Partitiori Chromatograph! 1 Added, Alcohol Methyl Ethyl n-Propyl n-Butyl n-9myl
mg.
%
17.7 18.2 17.0 15.1
97.0 89.4 90.7 89.9
..
3
2
Rec..
..
Added,
Rcc.,
mg.
%
17.7 18.2 17.0 15 1
87.0 91.7 96.1 101.9
..
..
Added,
Rec.,
mg.
so
20.4 18.7 25 1 18.9 19.4
82.8 102.1 103.2 111.1 104.7
Table 111. Analysis of Glycol Mixtures by Partition Chromatography Alixture S o .
1
2
3
Glycol Components 1,2-But ylene 2,a-Butylene 1,2-Propylene Ethylene 1,%Butylene 2,3-Butylene 1,2-Propylene Ethylene 1,2-Butylene 2,a-Butylene 1.2-Propylene Ethylene
Iinon-n 2.0 2.3 2.2 93.4 8.3 8.8
Composition. % Found Recovery 2.2 2.3 2.8
110 100
8.8
..
126
. .
73.2 14.0
8.0 9.7
100 91 99
20.2
18 1 1U.P
18.0 20.0
106 103
9.8
43.0
..
..
...
101
...
110 ml. of 1 to 4 n-butyl alcohol-chloroform 100 ml. of 1 to 1 n-butyl alcohol-chloroform 60 ml. of n-butyl alcohol Each of the solvents is equilibrated with an equal volume of water before use and added to the column when about 10 ml. of the previous solvent remains. Successive 10-ml. fractions arc collected using a flow rate of 2 to 3 ml. per minute. Normally, pressure is not required to attain this rate. When the last fraction is collected, the column stopcock is closed and the column retained until it has been established that all of the ethylene glycol (if present) has been eluted. If some ethylene glycol remains on the column, it is removed by percolating more nbutyl alcohol through the adsorbent, collecting several additional fractions. Analysis of Fractions. Each percolate fraction is transferred to a 500-ml. widemouthed Erlenmeyer flask and 10 ml. of 0.0551 sodium metaperiodate solution are added. The solutions are allowed to stand 25 minutes with occasional swirling. One hundred milliliters of water, 2 ml. of Alizarin Yellow R indicator solution, and washed, crushed ice are added. Enough ice should be present to maintain the temperature of the sclution a t about 0" C. during the subsequent titration. Excess periodate is titrated with 0.05N sodium hydroxide to the indicator change from yellow to orange. The first five fractions may be discarded. The next three fractions are collected and used as blanks for the titration. The glycols appear in subsequent fractions as shown in Figure 3. The glycol content of each fraction is calculated from the equation : Glycol, mg. = (XaOH ml. blank - NaOH ml. sample) X normality S a O H X mol. a t . of glycol DISCUSSION
llonohydric alcohols are determined in the chromatographic fractions by means of dichromate oxidation. Oxidation equivalents of a number of alcohols are given in Table I. -4s can be seen from these values, between 2 and 6 equivalents of dichromate are involved in oxidation. Isopropyl alcohol is oxidized to acetone. Although most of these oxidation equivalent weights are empirical, they are reproducible. Identification of a chromatographic peak is made from its location on a chromatogram such as Figure 2. I n this experiment, approximately 20 mg. of each alcohol were added to the column and separated by the recommended procedure. Excellent resolution of the mixture was obtained, the alcohols appearing in this order: n-amyl, n-butyl, n-propyl, ethyl, and methyl. Attempts were made to improve the separation between amyl and butyl alcohols by the use of less polar solvents, particularly hydrocarbons, but without success. When mixtures of isopropyl and n-propyl alcohols were subjected to the separation procedure, no resolution was obtained. Similarly no separation occurred
3.0
I
8
:I O m :I
0
E
6
7
Figure 3.
8
9
IO
I1
I2
13
14 I5 16 17 FRACTION NO. NO
IS
I9
20
ZI
22
23
24
Separation of Cz to Ca Glycols by Partition Chromatography
V O L U M E 2 5 , NO. 1 2 , D E C E M B E R 1 9 5 3 Compounds such as diethylene glycol and l,4butylene glycol (1,i-butanediol) do not interfere with the separation and detection of the glycols studied in this work. It is possible that these and other nonvicinal glycols can be separated by partition chromatography, but this study will require the development of an accessory method for their determination. Dichromate oxidation was considered for this purpose but could not be used because of the n-butyl alcohol present in the developing solvents.
1877
H. T. J. Littleton and R. W.Wheatcroft for permission to describe the apparatus in Figure l. The able assistance of Anne Greco also is gratefully acknowledged. LITERATURE CITED (1) Dal Sogare, (1952).
Stephen, and Oemler, A. K.,- 1 ~ 4 CHEM., ~. 24, 902
ACKNOWLEDGMENT
( 2 ) llarvel, C . S., and Rands, R. D., Jr., J . A m . Chem. SOC.,72, 2642 (1950). 1 3 ) Seish, .1.C.. Can. J . Chem., 28, 535 (1950). (4) Ihzd., 29, 552 (1951).
The author wishes to thank John Mitchell, Jr., and L. W. Bafranski for their interest and encouragement in this work, and
RECEIVED for review June 4 , 1963. Accepted September 75, 1953. Presented before the Division of Analytical Chemistry a t the 122nd Meeting SOCIETY, .&tlantic City, S . J.. September 1952 of the . h E R I C A N CHEMICAL
Determination of Elemental Fluorine IR\-ING SHEFT, HERBERT H. HY414N, AND JOSEPH J. KAT% C h e m i s t r y Division, Argonne 'l'ational Laboratory, L e m o n t , I l l . i n connection with an investigation of halogen fluorides, i t appeared practical to adapt the brominefluorine reaction as an analytical method for fluorine. Bromine, dissolved in bromine trifluoride, can be titrated with fluorine gas at room temperature. The reaction is quantitative and the end point is readily detected by the discharge of the bromine color. Using this procedure, the purity of several fluorine samples has been determined to &t%CJ,. The uncertainty of the titration, which is limited by the error in reading the fluorine pressure, should be reducible to about 0.1% by use of a more sensitive pressure-measuring device. It is possible to employ the titration to determine bromine, or substances which yield bromine on reaction with bromine trifluoride. These include metals, oxides, and halides other than fluorides. The titration can also be adapted for the determination of bromine pentafluoride.
sis of the inert components. Bibliographies and additional methods of analysis have recently appeared in the literature (3, 6 ) . In the course of other work, a procedure has been developed rhich can readily be applied to fluorine determination. This method depends on the fact that elemental fluorine reacts smoothly and quantitatively with bromine in the liquid phase 2Br2 + 2BrF3. Bromine triaccording to the reaction 3Fz fluoride (boiling point 127" C.) itself is an excellent solvent for carrying out this reaction. The method involves the titration of a known amount of bromine dissolved in bromine trifluoride with the fluorine gas to be analyzed. -4visual end point, the disappearance of the red-brown bromine color to give the light
+
VACUUM LINE
(L-4
F
LUORISE is usually prepared by the electrolysis of a molten potassium fluoride-hydrogen fluoride bath, using a steel cathode and a carbon anode (1) Fluorine so produced contains hydrogen fluoride from the bath. carbon fluorides from reaction with the anode, and air due to leakage. The hydrogen fluoride is easily removed from fluorine by treatment with sodium fluoride. The other contaminants. hen-ever, are very difficult to remove, and laboratory-generated or commercial tank fluorine will contain variable amounts of these almost unavoidable impurities. For many purposes it is important to know the purity of the fluorine, but many investigators have neglected fluorine purity because of the difficulties of analysis. At present two methods of fluorine determination are commonly used. The first consists of reaction of a known volume of fluorine mith mercury and measurement of the residual gas after fluorine has been converted to mercury fluoride ('7). The second consists of reaction of a known volume of fluorine with sodium chloride and determination of the chloride by absorption in alkaline arsenite (6). The first method has several drawbacks, most important of which is the formation of a mercury fluoride scum on the surface of the mercury. This makes readings of the mercury level difficult and inaccurate, especially where fluorine is a major constitutxnt. This method is primarily useful for the determination of emall amounts of fluorine in other gases inert to mercury. The second method is complicated and involves a rather large number of chemical operations. Loss of some of the residual gases in the various absorbents can lead to error in analy-
FP
CYLl N DER
ITRATION
CELL
Figure 1. Diagram of Apparatus
yellow of a fluorine-saturated bromine trifluoride solution, is easily discernible. The inert components can then be collected if desired for further analysis. This titration analysis is especially useful where fluorine is the major constituent. MATERIALS
The bromine trifluoride was obtained from the Harshaw Chemical Co. and purified by vacuum distillation in a nickel still. Bromine, bromine pentafluoride, hydrogen fluoride, and nonvolatile fluorides are the major impurities. The fraction used (boiling point 95-95.5' C. a t 250 mm.) was pale yellow in color and was stored in a welded nickel container. The fluorine was obtained from the Pennsylvania Salt Co. and was used directly from the tank. The purity of the fluorine in two cylinders employed in this work was greater than 99%. Another
