Anal. Chem. 1994,66, 40974099
Potassium Separation from S-Block and Other Elements Using a Polymeric Crown Ether B. S. Mohite,' D. N. Zambare, and B. E. Mahadik Environmental Analytical Chemical Laboratory, Department of Chemistry, Shivaji University, Kolhapur-4 16 004, India
A very simple column chromatographic separation method has been developed for potassium. The separation of potassium was carried out using poly(dibenz0-18-crown-6)with hydrobromic acid medium. Large amounts of sodium and rubidium were separated from trace level potassium. Potassium was separated from a number of associated elements in tertiary and four-component systems. The proposed method was extended to the analysis of potassium in various rocks and biological and medicinal samples. The method is very simple, rapid, selective, and reproducible. The reproducibility of the method is f2%. Crown compounds are applied in liquid chromatography. However, relatively little information is available1-5concerning the use of crown ethers, crown ether-modified silicas, and polymeric crown ethers for column chromatographic separation of potassium from other elements. One area of thecation separations field in which almost all present systems have difficulty is that of separations from acidic matrices. Polymeric crown ethers provide the means for selective cation separations from acidic matrices because they possess special features such as high resistance to chemicals, to temperature, and also to polar solvents such as acetone, alcohols, etc. Taking advantage of these attractive properties of poly(dibenz0- 18crown-6) (P(dbl8c6)), we have reported column chromatographic separation studies of molybdenum(VI),6 uranium(VI),7 and lead8 from hydrochloric acid medium. This paper describes in detail the separation of potassium from a number of other elements using poly(dibenz0- 18-crown-6) in hydrobromic acid medium.
EXPERIMENTAL SECTION Instrumentation, Column Material, and Reagents. The instruments and chemicals used were similar to those reported Procedure. An aqueous sample solution containing 100 pg of potassium was mixed with HBr to get a concentration (1) Fernando, L. A.; Miles, M. L.; Bowen, L. H. Radiochem. Radionanal. Lerr. 1919, 38, 387-394. (2) Nakajima, M.; Kimura, K.; Hayata, E.; Shono, T. J. Liq. Chromarogr. 1984,
7,2115-2125.
(3) Kimure, K.; Nakajima, M.; Shono, T. J. Polym. Sci. Polym. Chem. Ed. 1985, 23, 2327-2331. (4) Yagi, K.; Sanchez, M. C. Makromol. Chem. Rapid Commun. 1981,2,311315. ( 5 ) Igawe, M.; Ito, I.; Tanaka, M. Bunseki Kagaku 1980.29, 58G584; Chem. Absrr. 1980, 93, 21488239. (6) Mohite, B . S.;Patil, J. M.; Zambare, D. N. Talanra 1993, 40, 1511-1518.
(7) Mohite, B. S.;Patil, J. M.;Zambare, D. N.; Mali, U.G . Bull. Chem. Soc. Jpn. 1993,66, 3639-3642. (8) Mohite, B. S.;Patil, J. M.; Zambare, D. N . J. Indian Chem. SOC.1994, 71, 289-291. (9) Mohite, B. S.;Khopkar, S . M. Indian J. Chem. 1983, 2 2 4 962-964.
0003-2700/94/0366-4097$04.50/0 0 1994 American Chemical Society
of 0.5-8.0 M in a total volume of 10 mL. The solution was passed through a P(db18c6) column, preconditioned with HBr of the same acidity as that of the sample solution, at a flow rate of 0.5 mL/min. The column was then washed with HBr of the same acidity to remove unadsorbed cations. The adsorbed potassium was eluted with different eluting agents (described latter) at a flow rate of 0.5 mL/min. Fractions of 5 mL each were collected, and, after evaporation, the effluent residue was extracted with water. The potassium content of the residue was determined by flame emission spectroscopy at 767 nm.lo The concentration of potassium was computed from the calibration curve.
RESULTS AND DISCUSSION Effect of HBr Concentration upon Adsorption of Potassium on Poly(dibenz0-18-crown-6).Adsorption studies were carried out by varying HBr concentrations from 0.5 to 8.0 M in a total volume of 10 mL. A 100 pg sample of potassium was loaded. After adsorption, potassium was eluted with 0.1 M HCl. Potassium was adsorbed to the extent of 90% at 0.5 M HBr and 97% at 1.0 M HBr. The adsorption of potassium was quantitative (100%) from 1.5 to 8.0 M HBr. For routine work, 3.0 M HBr was used. Effect of Various Eluting Agents upon Potassium Elution Behavior. After adsorption, potassium from the column was eluted with different eluting agents such as HBr, HClO,, H2SO4,and CH3COOH. The results of elutions are shown in Figure 1. The elution of potassium was quantitative (100%) with 0.1-8.0 M CH3COOH and 0.1-8.0 M H2SO4. With 6.0 M HCl, the elution of potassium was 92%. With 8.0 M HCl, it was 83%. Potassium was not eluted with 0.1-3.5 M HC104. There was only 18% elution with 4.0 M HC104. With 5.0 M HC104, the elution of potassium was 60%. Effect of Varying the Concentration of Potassium. The adsorption studies of potassium were carried out on a 1.O g P(db18c6) column with 3.0 M HBr. The concentration of potassium in the load solution (10 mL) was varied from 500 to 6000 pg. The adsorption of potassium was quantitative up to 3500 pg/lO mL of load solution. The adsorption was 98% at 4000 pg/10 mL, 92% at 4500 pg/lO mL, and 85% at 5000 pgl10 mL. The extent of adsorption decreased with increasing potassium concentration in the load solution. The adsorption capacity of P(db18c6) for potassium was found to be 8.951 mmol/g. Separationof Potassium from Binary Mixtures. An aliquot of solution containing 100 pg of potassium was mixed with (10) Dean, J. A. Flame Phorometry; McGraw-Hill: New York, 1960.
Analytical Chemistry, Voi. 66, No. 22, November 15, 1994 4097
601 60
40 20
0
13
0 (
-
20
30
-
40
- Volume HCI,
50 of
0
10
CH3CCCHI
W
20
eluent ml
30
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40
50
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Figure 1. Elution studies of potassium.
foreign ions. HBr was added to get a concentration of 3.0 M in a total volume of 10 mL. The tolerance limit of various foreign ions was set as the amount of foreign ion required to cause f 2 % error in the recovery of potassium. The solution was passed through a P(dbl8c6) column, preconditioned with 3.0 M HBr, at a flow rate of 0.5 mL/min. Subsequently the column was washed with 25 mL of 3.0 M HBr to remove unadsorbed cations. Those foreign ions which were not adsorbed passed through the P(dbl8c6) column. Among alkali and alkaline earth metals, lithium, cesium, beryllium, magnesium, calcium, and strontium were not adsorbed, while sodium, rubidium, and barium were adsorbed along with potassium at various HBr concentrations. Sodium was not adsorbed at 0.5-1.5 M HBr, and the adsorption of sodium was only 10% at 2.0 M HBr but 90% at 8.0 M HBr. The adsorption of rubidium was 60% at 3.0 M HBr, and there was no adsorption of rubidium at 8.0 M HBr. Barium was, however, quantitatively adsorbed from 4.0 to 8.0 M HBr. With perchloric acid (6.0-8.0 M), potassium was quantitatively eluted but barium was not. Such an elution behavior of potassium and barium with perchloric acid was exploited for their separations from each other. Most of the alkali and alkaline earth metals showed high tolerance ratios (K:Mn+ for Li(I), 1:200; Na(I), 1:400; Rb(I), 1500; Cs(I), 1:llO; Be(II), 1:120; Mg(II), 1:200; Ca(II), 1:205; Sr(II), 1:180; Ba(II), 1:80). Among transition elements, only iron(II1) and molybdenum(V1) and, from the actinides, uranium(V1) showed adsorption along with potassium. There was no adsorption of iron(II1) from 0.5 to 2.5 M HBr. With 3.0 M HBr, the adsorption of iron(II1) was 4%, with 5.0 M HBr it was 50%, and it was quantitative from 6.0 to 8.0 M HBr. Molybdenum4098
Analytical Chemistty, Vol. 66, No. 22, November 15, 1994
(VI) showed no adsorption from 0.5 to 2.5 M HBr. At 3.0 M HBr, the adsorption of molybdenum(V1) was lo%, and it was quantitative from 5.5 to 8.0 M HBr. Potassium was eluted with 8.0 M HC104, but molybdenum(V1) was not. There was no adsorption of uranium(V1) from 0.5 to 4.0 M HBr, and adsorption was quantitative only with 8.0 M HBr. Most of the transition and inner transition elements were not adsorbed and showed very high tolerance limits. Among nontransition elements, only gallium(II1) and thallium(II1) showed adsorption at higher acidity, whereas lead was adsorbed at lower HBr concentrations. Most of the nontransition elements and also anions of inorganic and organic acids showed very high tolerance limits. Very good separation of a two-component system containing sodium and potassium was accomplished by passing a mixture containing 20 mg of sodium and 0.1 mg of potassium through a P(db18c6) column at 1.0 M HBr. Since sodium was not adsorbed, it passed through the column, leaving behind potassium on P(db18c6). The adsorbed potassium was then eluted with 0.1 M HC1. The separation of rubidium from potassium was carried out at 8.0 M HBr by passing a mixture containing 20 mg of rubidium and 0.1 mg of potassium through a P(db18c6) column. Rubidium was not adsorbed and hence passed through the column, and the adsorbed potassium was then eluted with 0.1 M HC1. Separation of Potassium from Multicomponent Mixtures. Separation of potassium from three-component systems was achieved using adsorption and sequential elution technique. The separation of mixtures containing lithium/beryllium/ magnesium/calcium/strontium, potassium, and barium was carried out by passing the mixture through a P(dbl8c6) column at 5.0 M HBr. At 5.0 M Hbr, Potassium and barium were adsorbed, whereas all other elements were not adsorbed. The adsorbed potassium was first eluted with 6.0 M HC104, followed by elution of barium with 0.1 M HCl. The separation of rubidium/cesium, potassium, and barium was achieved by passing the mixture through a P(db18c6) column at 8.0 M HBr. Potassium and barium were adsorbed, whereas rubidium/cesium were not adsorbed. The adsorbed potassium was eluted with 6.0 M HC104, and finally barium was eluted with 0.1 M HCl. Potassium was also separated from four-component mixtures. A mixture containing lithium/ beryllium/magnesium/ calcium/strontium, potassium, barium, and molybdenum(V1) was separated by passing the mixture through a P(dbl8c6) column at 6.0 M HBr. Only potassium, barium and molybdenum were adsorbed. Adsorbed potassium was first eluted with 8.0 M HC104, followed by the elution of barium with 1 M acetic acid, and finally molybdenum(V1) was eluted with 1.0 M NH40H. The separation of rubidium/cesium, potassium, barium, and molybdenum(V1) was accomplished similarly from 8.0 M HBr. Application to Analysis of Potassium from Geological, Biological, and Medicinal Samples. The proposed method was extended to the analysis of potassium in various samples. The rock, blood serum, and milk samples were opened and brought into solutions as described elsewhere." The known (1 1) Mohite, B.
S.;Khopkar, S.M. Anal. Chem. 1987, 59, 12OC-1203.
removed by washing the column with 1.OM HClOI. Potassium was eluted with 0.1 M HC1. The percentage of K20 found in various rock samples is shown in Table 1.
Table 1. Determination of Potassium in Real Sampler
Rock Samples K20 content, 7% sample
present
found
KC-1 1 KC- 12 USGS-G2 syenite-SY-2 basaltic-BR
2.15 4.30 4.52 4.51 1.41
2.16 4.27 4.51 4.45 1.44
Biological and Medicinal Samples K content, mequiv/L sample present found blood serum milk electral powder
5.10 75.4 20.0
5.08 15.5 20.14
amount of electral powder (oral rehydration powder) was directly dissolved in distilled, deionized water. The biological and medicinal samples were treated as per the general procedure using 3.0 M HBr. The amount of potassium found in triplicate analysis is shown in Table 1. An aliquot of rock sample solution was treated similarly as per the general procedure using 3.0 M HBr. Under these experimental conditions, only potassium was adsorbed quantitatively. Iron(III), which was adsorbed partially, was
CONCLUSION A very good separation of two-component systems (Na-K, Rb-K) and the separations of potassium from four-component systems were carried out using P(db18c6). Various cations from alkali and alkaline earth metals, nontransition metals, transition metals, and also anions of organic and inorganic acids showed very high tolerance limits. The method was extended to the analysis of potassium in a number of rocks and biological and medicinal samples. The method is very simple, rapid, selective, and reproducible. The recovery of potassium in all instances from triplicate determinations is 100 f 2%. The reproducibility of the proposed method is f2%. ACKNOWLEDGMENT We are thankful to the Council of Scientific and Industrial Research, New Delhi, India, for assistance and for sponsoring the project No. 01(1300)/93/EMR-I1. Received for review February 8, 1994. Accepted July 30, 1994.' 0
Abstract published in Aduunce ACS Absiraers, September 15, 1994.
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