1908
ANALYTICAL CHEMISTRY
degrees, provided P prior separation of paraffins and aromatics by silica gel is employed.
five-, and six-ring condensed cycloparaffins, noncondensed cycloparaffins, monocycloparaffins, isoparaffins, and n-paraffins.
n-Paraffins from isoparaffins. 2. Isoparaffins from condensed cycloparaffins. 3. Monocycloparsffins from noncondensed di- and tricycloparaffins. 4. Condensed dicycloparaffins from condensed polycycloparaffins. 5 . Free phenyls from aryl cycloparaffins and polynuclear aromatics. 6. Aryl cycloparaffins and free naphthyls from biphenyls, fluorenes, and tricyclic aromatics.
(1) Beale, E. S. L.. and Docksey, P., J . Inst. Petroleum, 2 1 , 860 (1935). (2) Brown, R. 4., .&NAL. CHEM., 2 3 , 4 3 0 (1951).
LITERATURE CITED
1.
Very little separation was obtained between isoparaffins and monocycloparaffins. This is believed to be due partially to the molecular weight range of the oil. As a result of the separations by both silica gel adsorption and thermal diffusion, the mass spectrometer analysis was able to resolve 16 different molecular compound species. These include tricyclic aromatics, fluorenes, biphenyls and/or acenaphthenes, free naphthyls, dihydronaphthalenes and/or dicycloparaffin benzenes, aryl cycloparaffins, free phenyls. two-, three-, four-,
(3) Brown, R. A , Doherty, W., and Spontak, J., Consolidated Engineering Corp., Pasadena, Calif., Group Rept. 84 (1951). (4) Brown, R. A . , Xielpolder, F. W., and Young, W. S., Petroleum Processing, 7, 204 (1952). (5) Fred, RI., and Putscher, R., ANAL.CHEM..2 1 , 901 (1949). (6) Haak. F. rl., and Van Nes, K., J . Inst. Petroleum, 37, No. 329, 245 (1951).
(7) Jonea, 9. L., Petroleum Processing, 6, 132 (1951). ( 8 ) .Jones, A. L., and Llilberger, E. C., Ind. Eng. Chem., 45, 2689 (1953). (9) O’Keal, 51. J., Jr., “Application of High ~lolecularWeight
Mass Spectrometry to Oil Constitution,” Conference on ;Ipplied Mass Spectrometry, London, England, Oct. 29 and 30. 1953.
(10) O’Neal, hi. J., Jr., and \Tier, T. P., Jr., ANIL. CHEM..23, 830 (1.9.51). .._ (11) Taylor, R. C., and Young, R. S.,IND.ESG.CHEM.,ASAL. En.. 17,811 (1945). RECEIVED for review May 24, 1954. .Iccepted September 27, 1954. €’re sented at the Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, hlarch 4, 1953. I .
Ion Exchange Method for Determination of Alkali Metals in Presence of Calcium and Magnesium OLOF SAMUELSON and E E R O S J a S T R 6 M Department o f Engineering Chemistry, Chalmerr Teknirka Hb’gskola, Gothenburg, Sweden
; irapid and accurate method has been evolved for deter-
mining potassium, sodium, and lithium in the presence of calcium and magnesium. The method is based upon the ability of ethylenediaminetetraacetic acid (EDTA) to give stable chelates with calcium and magnesium in water-ethyl alcohol solutions. The bivalent metals are taken up in a column filled with a mixture of an anion exchange resin in the ethylenediaminetetraacetic acid form and the acetate form. The alkali metals appear in the effluent which is passed directly through a second column containing an anion exchanger in the free-base form. The alkali hydroxides obtained in the effluent after the second column are titrated with standard acid. The determination can be carried out in less than 2 hours.
A
SIMPLE ion exchange method for the determination of
sodium and potassium in the presence of vanadium, iron, copper, nickel, and cobalt has been devised by Samuelson and Schramm ( 4 ) . The solution is passed through two columns coupled in series; the first column is filled with an anion exchanger in the citrate form and the second n-ith an anion exchanger in the freobase form. The alkali metals pass through the first column as citrates, whereas the other metals are transformed into citrate complexes which are strongly held by the resin. I n the second column the citrate ions are exchanged for hydroxyl ions. AMter washing the columns with water the alkali metals can he determined quantitatively by titrating the effluent x i t h standard acid. The separation can be performed in 1 to 2 hours and the accuracy is within about f 0 . 2 % . Calcium and magnesium have been found to behave largely in the same manner as the alkali metals (3). I t should be of considerable interest to work out a similar procedure for the removal of
calcium and magnesium from solutions containing the alkali metals. 9 certain uptake can be achieved by working a t high pH with resin in the citrate form but the complexes are not strong enough to permit a quantitative separation. Ethylenediaminetetraacetic acid (EDTA) is known to give more stable chelates with calcium and magnesium than citric acid and therefore complete uptake might be obtained using anion exchangers in the ethylenediaminetetraacetic acid form. However, when working with aqueous solutions, calcium and magnesium rn ere only slightly retarded in the column. Because the stability of the ethylenediaminetetraacetic acid chelates increases with an increase in pH, a mixture of resin in the ethylenediaminetetraacetic acid form and the freebase form would be expected to be more effective. This was confirmed by a series of experiments carried out as a combined batch and column operation. Under proper conditions a quantitative uptake could be obtained but when working n i t h a moderate excess of resin it was observed that, on washing with Tater, traces of calcium and magnesium appeared in the effluent. Ion elchange experiments carried out in the present investigation showed that the uptake of calcium and magnesium by the resin is much more effective in an alcohol-water solution than in pure water. The alkali metals are not taken up and can be displaced from the column by nashing with the solvent. I n this mannei it is possible to separate calcium and magnesium quantitatively from potassium, sodium, and lithium. In a second column the alkali salts are converted into hydroxides which arc’ determined by titration u ith standard acid APPAR4TUS
I t is important to have a resin of good chemical stability. The strongly basic resin Dowex 2 wa? used in the present investigation. I t is desirable not to have too long a time of contact between the resin and the solution 4n appropriate flow rate was obtained when the particle size of 0.30 to 0.54 mm. was used.
V O L U M E 2 6 , NO. 1 2 , D E C E M B E R 1 9 5 4
1909
This particle size is slightly larger than that used in earlier in~. vestigations ( 2 ) . The resin was placed in a large column and treated with 1.5M sodium acetate solution until the chloride ions had been disulaced from the column. After washing with water until the effluent was neutral toward methyl red, the wet resin was stored in a closed bottle. To transform the ion exchanger into the ethylenediaminetetraacetic acid form, 100 ml. of the resin was placed in a column and treated with 500 ml. of 0.2M solution of disodium ethylenediamine tetraacetate and finally washed with about 1500 ml. of water. I t is not necessary to continue the washing until the effluent is free from ethylenediaminetetraacetic acid. The hydroxyl form of the resin was prepared by passing 1000 ml. of 1.Y sodium hydroxide through a column containing 100 ml. of resin and subsequently washing with water; about 1000 ml. is required, to displace the alkali from the column. The resin was stored in a wet condition, In the earlier investigation with citrate complexes, t v o columns were coupled in series. The apparatus is described in Samuelson’s monograph (3). The dimensions of the resin bed for both columns were 9 X 170 mm. When filling the columns, the resin was suspended in 60% ethyl alcohol (by volume) and slurried into the columns. The resin is somewhat unstable and it is therefore necessary to wash with about 50 ml. of the solvent before the experiment is started. The swelling of the anion exchanger is greater in 60% ethyl alcohol than in pure water. For this reason the column should not be filled with a suspension of the resin in water because the increased swelling on the subsequent washing with the ethyl alcohol-water solution would cause an increased resistance to the flow. After the experiments, the resin is regenerated by means of 1.5M sodium acetate solution. The resin from a large number of experiments is collected in a large column and treated with the regenerant. ~
diaminetetraacetic acid form and the free-base form was used in these investigations. The solution t o be analyzed (50 ml. of S o l , ethyl alcohol) was brought into contact with about two thirds of the mixed resin for about 20 minutes, and stirred by hand several times. No precipitation occurred provided a sufficient amount of resin was used. If a precipitate occurred a further addition of resin was made to obtain complete dissolution. After the 20-minute period, the resin was slurried into the first column and the solution passed through the two columns. After washing with 60% ethyl alcohol the effluent from the second column was titrated.
EXPERIMENTAL
Anion Exchanger in Ethylenediaminetetraacetic Acid Form. Preliminary experiments with the resin in ethylenediaminetetraacetic acid form showed that a precipitation occurred when a solution containing calcium chloride or magnesium chloride in 60% ethyl alcohol was passed through the column. The precipitate plugged the column and the flow rate dropped considerably, but a satisfactory separation of calcium from potassium was possible. The precipitate consisted of the calcium salt of ethylenediaminetetraacetic acid contaminated with 10% or less of free ethylenediaminetetraacetic acid. In order to eliminate the plugging of the column the experiments were performed as a combined batch and column operation ( 2 ) . After stirring the sample solution with about two thirds of the resin for 30 minutes, the precipitate and the resin were slurried into the column. The effluent from the first column passed directly through the second column containing the resin in the free-base form. After washing the columns with 80 ml. of 60% ethyl alcohol the potassium hydroxide was titrated with standard acid. The time required for the ion exchange separations was about 2 hours.
Table I.
Separation of Potassium from Calcium and Magnesium by Resin in EDTA Form
Sample Soln ,
MI. 30 30 30 30 30 70 80 100 100 100
CaClz 0.5 0.5 1.0
.. ..
i.b ..
0:s
Added, RImole MgClz KC1 0.5 1.000 0.5 2.000 , . 2.000 1.0 2.000 2.0 2.000 1.0 2.000 .. 2.000 1.0 2.000 2.0 2,000 0.5 2.000
Found, Mmole KOH
Relative Error,
0,996
-0.4 -0.6
1.988 2.001 1.950 1.935 1.978 1.998 1.985 1 982 1 998
CI /G
Figure 1. Behavior of Potassium, Sodium, and Lithium during Washing Step
+
Column 1, 9 X 180 m m . ; Dowex 2 [ 50% EDTA 50%0 Ac-; 0.30 to 0.54 mm.] Column 2, 9 X 180 m m . ; Dowex 2 [OH-: 0.30 t o 0.54 m m . ] Influent, 1 mmole CaCIz 4- 2 mmole alkali chloride i n 50 ml. of 60%0 CgHsOH. Subsequently washing with 60% GHsOH Flow rate, 2 ml. per minute
The experiments showed that potassium could be easily displaced from the column in the washing step, about 100 ml. of the wash solution is required for a quantitative recovery. With sodium it was much more difficult to reach a quantitative displacement. After washing with about 400 ml. the recovery was complete. Lithium is the most difficult to displace; therefore, it is necessary to use at least 1000 ml. of the solution in order to displace the lithium ions from the column. The differences in the behavior of these three alkali metals during the washing step are illustrated in Figure 1. This procedure described is rapid for the determination of potassium in the presence of calcium and magnesium. The timp required for the separation is about 2 hours. Results in Table I1 show that the method is extremely accurate, the relative error being less than 0.2%.
+0.1
-2.5 -3.3 -1.1 -0.1
-0.8 -0 5
-0.1
The results presented in Table I show that a good accuracy is obtained with solutions containing calcium chloride whereas the recovery is incomplete in the experiments with a magnesium salt (confirmed by flame spectrophotometric tests after wet combustion of the precipitate). Mixed Anion Exchanger (EthylenediaminetetraaceticAcid + Free Base). A mixture of equal volumes of resin in ethylene-
__
-
~
-
~
Table 11. Separation of Potassium and Sodium from Calciuni and Rlagnesium by Mixed Resin (EDTA Free Base)
+
CaCIz 0.5 0.5 1.0 1.0 0.5
Added. Mmole .\IgCh KC1
KaC1
Found, Minole Alkali Hydroxide 2,002 2.001 2.004 2.001 2,001 1.990 1.995 1.996 2.008 1.986
Relative Error,
%
+O.l +O.l +0.2 +0.1 +0.; -0 J
-0.3
-0.2 1-0.4
-0.7
ANALYTICAL CHEMISTRY
1910 Table 111. Separation of Potassium and Sodium from Calcium and Magnesium by Mixed Resin (EDTA Ac-)
+
Added, Mmole MgClr KC1
CaCh
Found, Mmole Alkali Hydroxide
NaCl
Relative Error.
%
Tahle IV. Sewration of Sodium from Calcium and Rlagnesium-in Presence of Acids by Mixed Resin Ac-) (EDTA ~
+
Added, Mrnole CaClz MgClz HC1 HsPOi 0.5 0.5 0.5 0.5 0.5 0.5 0.5
0.5 0.5 0.5 0.5 0.5 0.5 0.5
0.5 1.0 1.5 2.0
..
... .
0:25 0.50 1.00
Found, 3Imole ______ NaCl
&‘ :
2.000 2,000 2.000 2.000 2.000 2.000 2.000
40,001
