Analysis, Wt. yo Run 1 R u n 2 R u n 3 R u n 4 Run 5 Run 6
Std." Dev.
added to the HIBA concentration. This sum has been found to be constant with time, and it affords a good long-range check on the analysis.
HIBAb 17.2 17.5 1 7 . 5 17.2 1 7 . 3 1 7 . 4 Oxalic acid 0.31 0 . 3 3 0 . 3 7 0.35 0 . 3 5 0.33 a-Acetoxyisobutyric acid 1.19 1 . 2 3 1 . 2 3 1.24 1.22 1.20 a-Nitratoisobutyric acid 0.36 0.38 0 . 4 3 0 . 3 8 0 . 4 3 0 . 3 7 Nitro-tert-butyl alcohol 0.21 0.20 0 . 1 8 0.24 0.23 0 . 2 2 a-( ~~'-Hydroxyisobutyroxy) isobutyric acid 0.33 0.33 0.35 0.39 0.33 0 . 3 3 Estimated from range. * Sum of hydroxy and methoxy derivatives.
0.12 0.02 0.02 0.03 0.02
The authors thank Escambia Chemical Corp. for giving them permission to submit this paper for publication.
Table 111.
Repeatability for Six Consecutive Determinations
Compound
isobutyrate. This is the only byproduct of the esterification which has been detected. When a sample is analyzed, HIBA is reported as the sum of the hydroxy and methoxy derivatives. Calculation of Analyses. Concentrations of the individual components, on a n absolute basis, are ca1,culated from the following relationship: Concentration (wt. %)
=
S.F. X
Ria
X
Rph
where Ria
=
100 X weight of internal standard
weight of sample RESULTS AND DISCUSSION
Four analyses of synthetic blends, based on a minimum of three runs, are shown in Table 11. The accuracy of the method, as indicated by such analyses, has consistently been +2% relative or better. Synthetic blends have been the only check on accuracy, because no suffi-
ACKNOWLEDGMENT
0.02
ciently accurate alternntii (I x i d y t i ( a1 method wac available t o LISP as a chwk This same degree of accuracy is achieved a h e n nitric acid, acetic acid, and water are added to these blends. The esterification reaction products of nitric acid, acetic acid, and water, along with the solvent acetone, are eluted between 0.3 and 0.5 minute (Table I), and have no effect on the chromatograms. The short-range repeatability of the analysis is indicated in Table 111, which tabulates six consecutive analyses obtained within 3 hours. Hydrolysis of several of the components occurs when a sample stands for any length of time. Because of this, it is difficult to check the long-range precision for individual components by analyzing a single sample over a period of time. In practice, the concentrations of all components which form HIBB upon hydroly,'Q I S are expressed as milliequivalents per gram of potential HIBA, and their sum is
LITERATURE CITED
(1) Arndt, F., "Organic Syntheses," Coll. Vol. 2, 8. H. Blatt, ed., p. 165, JViley, New York, 1943. (2) Bartsch, R. C., Miller, F. D., Trent, F. >I., ANAL.CHEM.32, 1101 (1960). (3) Emery, E. VI., Koerner, W. E., Ibid., 33, 146 (1961). (4) Hill, U. T., Ibid., 18, 317 (1946). (5) Horning, E. C., Moscatelli, E. H., Sweely, C., Chem. & I n d . (London) 1959. 751. (6) Hunter, I. R., Hawkins, N. G., Pence, J. W., ANAL. CHEM.32, 1757 (1960). (7) Hunter, I. R., Ortgen, V. H., Pence, J. W., Ibid., 32, 682 (1960). (8) James, A. T., Martin, A. J. P., Biochem. J. 50, 679 (1952). (9) Loyd, R. J., Ayres, B. O., Karoseck, R. W., 27th Meeting Gulf Coast Spectroscopic Group, Houston, Tex., Oct. 2, 1959. (10) Metcalfe, L. D., Nature 188, 142 (1960). (11) Schlenk, Hermann, Gellerman, J. L., ANAL.CHEM.32, 1412 (1960). (12) Schoenbrunn, E. F., Gardner, J. H., J. Am. Chem. SOC.82, 4905 (1960). (13) Smith, L. I., Chem. Revs. 23, 193 (1938). RECEIVEDfor review Julv 3, 1961. Accepted October 25, 1961. Pittsburgh
c.
Conference on Analytical Chemistry and Applied Spectroscopy, February-March 1961.
Separation of the Alkali Metal Cations from Mixtures of Various Cations by Electrochromatography JOSEPH SHERMAl and HAROLD H. STRAIN Argonne National Laboratory, Argonne, 111. b Differential electrical migration in an ammoniacal solution of ammoniatriacetic acid containing cyanide facilitates the separation and estimation of the alkali metal ions from other univalent ions (silver, thallium, and mercurous) and from all multivalent ions as well. Migration from this aqueous solution into and through a nitromethane solution provides for the separation of the alkali metal ions from one another as well as from the All the separated alkali mixture. metal ions may b e located and estimated by flame photometry. Sodium, potassium, rubidium, and cesium may b e detected and estimated b y neutron activation followed by gamma-ray spectrometry.
76
ANALYTICAL CHEMISTRY
0
of the research problems of this laboratory involves the development of electrochromatographic methods for the separation of one or a few metal ions from complex mixtures. Previous reports have shown: that the alkali metal ions are partially separated from one another and from various alkaline earth ions by electrochromatography in aqueous solutions containing ammonium salts of comples-forming acids (4); that sodium, potassium, rubidium, and cesium can be completely separated from one another by electrochromatography in nonaqueous solvents such as nitromethane (8); and that the univalent ions of silver and thallium can be separated from each other and from various multivalent ions NE
by migration in a n aqueous solution in which complexing and p H control are employed (7). This paper is concerned with a n extension of these observations, so that all the alkali metal ions can be separated quantitatively in aqueous solution from univalent silver, thallium, and mercurous ions as well as from various multivalent ions. Quantitative determination can be made by flame photometry or activation analysis. iilkali metal ions can be separated from one another as well as from the rest of a complex mixture by migration from
1 Present address, Department of Chemistry, Lafayette College, Easton, Pa.
n
n
I
U
Figure 1. Arrangement for quantitative electrochromatographic separation and recovery by subsequent elution A.
6. C.
D.
15
Paper wings for reserve electrolyte Graphite electrodes Strip for application of sample Drip point to be cut later for elution of ions Region far migration of alkali metal ions
watw into and through nitromethane in a coupled aqueous-nonaqueous system. EXPERIMENTAL
Stabilization Medium. Commercial wood-pulp filter paper (EatonDikeman Co., Grade 301; 0.030 inch thick) nns employed as the stabilization medium. It !$as prepared for use by mashing several sheets (2 by 6 feet) with 6 liters of I N nitric acid folloned by 24 liters of distilled water as previously described ( 7 ) . Migration Apparatus. With due precaution against contamination, especially from sodium, the paper was cut to the required size and shape for each experiment. Except in one experiment discussed in another section, the paper was used either in rectangular shape or in the form of a n H as described below. The H-shaped paper n a s used for the separation of the alkali metal ions from mixtures of various other ions; the rectangular paper was used for the separation of the alkali metal ions from one another as uell as from the mixture. It was placed on a water-cooled copper plate (7) and saturated with the background solution to be used. The excess solution \T-as removed. Sample spots were applied a t previously marked positions on the paper, which was covered with a polyethylene sheet. The electrodes employed were blocks of nuclear-reactor graphite (Grade CS), 44 x 5 x 1.3 em. These were placed directly on the ends of the moist paper and connected to a source of high-voltage direct current. Most migrations were performed a t a potential of about 10 T7olts per em. of paper. For the quantitative separation of the group of alkali metal ions employing the aqueous solvent described below, the paper was cut in the shape of an H, as shown in Figure 1. The electrodes, B , were placed on the large wings,
A, which contained reserve electrolyte that prevented the current from dropping rapidly during the course of the migration. A 0.5-em. strip, C, onto which the sample solution could be applied 'cvas cut from the dry paper. This strip containing the partially airdried sample was placed between the moistened sections of paper prior to applying the voltage. I n this way up to 500 pl. of sample solution could be applied to a relatively small section of the paper with no possibility of spreading into a wide zone. Bfter migration for the proper time, the electrode was removed from the right wing and the paper cut on the dotted line to provide a drip point, D, for the subsequent elution of the alkali metal cations from area E. This elution was performed by placing the paper b e h e e n polyethylene sheets taped to an inclined glass plate. A paper wick from a reservoir of distilled water above the plate was connected to the top of the paper, and the eluted material was collected in a volumetIic flask as it issued from the drip point on the bottom. All the ions in area E could be theoretically removed by elution with one paper-volume of water, assuming no adsorption of the ions by the paper. To be safe, 25 ml. of effluent was collected; this represented just over twice the volume of liquid required to moisten a piece of paper of this size. For the separation of the alkali metal cations from various other ions and from one another in coupled aqueous-nonaqueous systems, rectangular sheets of paper (30 X 90 cm.) were employed. The dry paper was cut lengthwise 25 cm. from the left (anode) end. and the two edges along the cut were frayed by lightly running a sharp object along them, This made it easier to rejoin the pieces later on. The left part of the paper vas treated with the aqueous background solution and the right part with the nitromethane solvent. The sample spots were applied 22 em. from the anode end of the paper (3 em. from the cut end). The two pieces of paper were butted together, the junction was smoothed out, the electrodes were placed at the ends, and the migration was then carried out as usual. Background Solutions. Two background solutions were used in this work. One was a n aqueous solution which was 0.0125M in ammoniatriacetic acid (nitrilotriacetic acid), 0.1-44 in ammonia, and 0. 051M in hydrocyanic acid ( 7 ) . The other Fas a nitromethane solution, 0.2.11 in ammonium formate and 0.4111 in trichloroacetic acid (8). Initial Zones. Test solutions of the alkali metal and silver, thallium, and mercurous ions were prepared by dissolving the proper amount of the reagent-grade nitrate, chloride, or acetate. Solutions of sodium, potassium, rubidium, and cesium tracers were prepared by dissolving weighed quantities of the nitrates which had been irradiated by the staff of the Argonne CP-5 reactor. For this purpose, the weighed nitrate was placed in the
QUARTZ-WOOL PLUG-
R
QUARTZ-WOOL PLUGS
SAMPLE
u
I cm
Figure 2. Apparatus for irradiation of alkali metal salts Thin-walled quartz tubing pure quartz wool
with plugs of
inner of two quartz tubes as shown in Figure 2. The tubes were packed in an aluminum container which was wired closed for insertion in the reactor. After irradiation, the aluminum container was opened and the inner quartz tube removed and clamped upright over a flask containing a known volume of water. A rubber tube, attached to a T-tube and a rubber bulb, was placed over the top of the quartz tube. By proper manipulation of the rubber bulb and T-tube, water was sucked up and expelled until all the solid was dissolved and transferred to the flask. Sample solutions were applied as spots from micropipets. In the quantitative studies, care was taken to rinse the pipets with several portions of distilled water to assure quantitative transfer of the sample to the paper strip. When synthetic mixtures were separated, these mixtures were prepared beforehand and put on the paper as a single spot, or the mixture was prepared on the paper by placing a number of individual spots on the same area. In all cases where mixtures mere separated, positive identification of the constituents was assured by placing reference spots of pure material on the same chromatogram. Detection of Zones. Various methods were employed for the detection of the zones in the paper after migration of the solutes had taken place. Ions of silver, thallium, and mercury were made visible by spraying with a 2% aqueous solution of yellow ammonium sulfide, which produced greenish brown, orange-brown, and black sulfide spots, respectively. Hydrogen peroxide (5 pl. of a 3% solution), added to detect any electroosmotic flow, was located with alkaline ammoniacal silver nitrate (0.1M silver nitrate in 2 X ammonia, mixed with an equal volume of 611 sodium hydroxide) (9). VOL. 34, NO. 1, JANUARY 1962
a
77
w 70 c
aQ
r
60
4
a
f
50
I
50
40
LL
3o
c
Figure 3. Smooth scan of nitromethane portion of electrochromatogram
0
0
.\o
C/S
I
20
d', 5 0 c/s
0
0
1
2
3
4
5
6 7 8 INCHES
9
1
The most satisfactory method for the detection of lithium (also useful for the detection of sodium) was a spray of an aqueous solution of zinc uranyl acetate to which 25% of absolute methanol had been added (6). The chromatogram was dried, sprayed, and dried again, and the resultant bright fluorescent spot viewed in a darkened room under ultraviolet light. Radioactive zones were located by scanning the paper with a portable, battery-powered radiation survey meter held in the hand. The detection tube was encased in a lead sheet with a narrow slit. When a permanent record of the positions of the zones was desired, the moist chromatogram was wrapped in polyethylene and drawn under a Geiger-Muller tube in a mechanical scanning apparatus which continually advanced the paper strip a t 1 inch per minute and graphically recorded the radioactivity on a synchronized Brown potentiometer. Quantitative Analysis. Flame photometric determinations of lithium and mixtures of sodium and potassium after elution from the paper (Figure 1) were performed mith a Beckman flame photometer. Esploratory studies of the usefulness of activation analysis (5) for sodium, potassium, rubidium, and cesium were made by spotting standard amounts of the nitrates a t various places along a strip of washed paper. The paper was covered with polyethylene, rolled up, and wrapped in aluminum foil prior to irradiation in the Argonne CP-5 reactor. After irradiation, the active spots to be studied were cut from the paper, mounted on cardboard, and examined with a y-ray spectrometer (3 X 3 inch XaI crystal) with the help of the analytical group of the laboratory ( 2 ) . RESULTS A N D DISCUSSION
Studies with Radioactive Tracers. Figure 3 shows the results of separating a mixture of active alkali metal ions and silver and thallium ions in a coupled aqueous-nitromethane system on the rectangular paper as described above. Various amounts of the alkali metals were mixed together on the 78
Background solutions. 0.01 25M ammonia-triocetic ocid, 0.1 M ammonia, ond 0.05M hydrocyanic acid in water; 0.2M ammonium formate and 0.4M trichloroacetic acid in nitromethane Mixture. 20 pl. of 0.02M No; 200 pl. of 0.02M K; 1 pl. of 0.02M Rb; 1 PI. of 0.02M Cs; 10 pl. of 0.05M TI; and 10 pl. of 0.05M Ag Potential. 1000 volts ( 1 1 vo/ts/cm.) Migration time. 6 hours. (Activity in counts per second for each ion is % of counting rate times counting rate shown for that ion)
ANALYTICAL CHEMISTRY
0
1
1
1
2
paper because the level of activity of each a t the time of the experiment was different, and it was necessary that all fall within the range of the scanning apparatus. The actual distances of migration toward the cathode of the centers of the spots from the point of application were: sodium, 9.8 em.: potassium, 17.0 em.; rubidium, 28.5 cm.; and cesium, 34.0 em. Spraying the aqueous portion of the electrochromatogram with yellow ammonium sulfide proved that silver and thallium were complexed and migrated as anions, as would any multivalent ions included in the mixture (7). Separate studies with mercurous ion showed that it too separates from the alkali metals in such a system. Univalent mercury is unstable in ammoniacal solutions and in the presence of cyanide, decomposing to mercury and mercuric ions. The mercury was noted as a black spot which did not migrate from the origin; the mercuric ion was complexed by cyanide and migrated as an anion, being located with the sulfide spray. Since there is no radioactive tracer suitable for the detection of lithium, separate studies of its migration relative to that of sodium were made under conditions identical with those of Figure 3. Both lithium and sodium could be detected by spraying the dried chromatogram with zinc uranyl acetate solution and viewing under ultraviolet light. The limit of detection under the conditions employed was an initial zone containing 0.005 mole of lithium and 0.003 mole of sodium. As n as t o be expected from the results of Figure 3, which shows that the mobility of the alkali metals increases with increasing atomic weight, lithium always trailed sodium by 1 to 2 em. in the experiments conducted. Since sodium always formed an extremely narrow zone under these conditions, lithium and sodium were completely separated. I n the course of these studies in which the dried paper was viewed under ultraviolet light, there was indication that
some nater had flowed into the nonaqueous side of the electrochromatogram after the two portions had been joined. A bright fluorescent front !?as visible on the nitromethane side running across the paper. It was not necessary to spray with zinc uranyl acetate t o view this fluorescence. Under the conditions of Figure 3, this front was coincident with the sodium front, which appeared as a brighter area in the sprayed papers. With other migration periods the sodium front and the fluorescent front did not coincide. The formation of this front is associated with the flow of a liquid into the paper. I t was obtained by alloning any liquid (including distilled water) t o flow part n ay into a strip of paper, M hich w-as either dry or soaked first in one of the background solutions used. On drying and viewing under ultraviokt light, a bright line was visible a t the place 13 here the flow of wash liquid stopped. This was noted with many liquids and several types of filter paper besides the one used in this work. The fluorescent front was not apparent until the paper was dried. That this is due to the presence of something in the paper is indicated by the fact that this front is much more prominent when paper which had not been prenashed with acid LT as used. Another indication of a flow of water into the nitromethane was found M hen hydrogen peroxide n-as spotted a t various points along the spliced chromatogram: a t the normal point of sample application on the aqueous side; 1 em. to the right of the junction; and 25 em. to the right of the junction on the nitromethane side. The spot on the aqueous side and the one far removed from the splice on the nonaqueous side showed virtually no movement, as expected when the electrodes are placed directly on the paper (9). The spot nearest the splice showed 4- to 5-em. movement toward the cathode, however, indicating a considerable flow of solution a t this point. Other reagents for detecting lithium
3cm. F
E
Figure 4. Arrangement for quantitative electrochromatographic separation and recovery without elution (1). Topview (2). Side view (thicknesses not to scole) A. 6. C.
D. €.
F.
Filter poper Graphite electrode Strip for application of sample Region for migration of alkali metal ions Beaker containing background solution for collection of Ions Platinum-wire electrode
in a sheet of filter paper were tested before the zinc uranyl acetate spray was chosen. Violuric acid (3) and chloranilic acid (1) were unsuitable, because each reacted with the ammonium ion, in excess in the background solutions, as well as with the lithium. Even in the absence of ammonium ion, neither test proved as sensitive Cor lithium as zinc uranyl acetate. Quantitative Studies. K i t h the use of flame photometry for estimation of the alkali metals after migration, it is only necessary to separate the ions from the mixture and not from each other, since the analytical method is capable of determining each ion in the presence of any mixture of the others. With n n H-shaped chromatogram soaked in the ayueous solvent, all alkali metal cations in a mixture added to the sample strip migrate into area E , Figure 1, n-hile all the other metal ions move tonard the anode. The ions are thrn eluted from area E with water and the elucnt is analyzed by flame photometry. The accuracy of the method i s limited only by the error inherent in the determination of the metals in the presence of each other. Separate experiments vere run in which 1 pl. each of 0.02.11 radioactive rubidium and cesium (20 mr. per hour) were spotted on the sample strip and 300 volts applied for 30 minutes. In each case, the point of maximum activity moved 9.0 cm. toward the cathode, and the sample strip became completely free of radioactivity (
