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Anal. Chem. 1907, 5 9 , 1737-1738
AIDS FOR ANALYTICAL CHEMISTS Composite Ion Exchanger for Removal of Sodium-24 in Neutron Activation Analysis of Biological Materials Aleksander Bilewicz, Barbara Bartoci, and Jerzy Narbutt* Department of Radiochemistry, Institute of Nuclear Chemistry a n d Technology, 03-195 Warsaw, Poland
Halina Polkowska-Motrenko Department of Analytical Chemistry, Institute of Nuclear Chemistry a n d Technology, 03-195 Warsaw, Poland Sodium-24, predominating in the y spectra of neutron-irradiated samples of biological materials, ought to be removed from the samples, making it possible t o detect other radionuclides of analytical interest. Crystalline hydrated antimony pentaoxide (HAP) is commonly used for this purpose. T h e procedure consists of passing a hydrochloric acid solution of an irradiated sample through a small column filled with HAP grains on which sodium ions are selectively adsorbed (I). However, like other inorganic ion exchangers, crystalline H A P exhibits some serious shortcomings which limit its application. Poor mechanical stability of the HAP grains results in clogging the column with pulverized HAP particles in the course of eluting, especially with more concentrated HC1 solutions (2). The process of ion exchange on HAP is characteristic of poorer kinetics than that on ion exchange resins. T h e retention capacity, below 2 mequiv of Na+/g of HAP, lower than the calculated value of 5.06 mequiv/g (3),indicates that only a fraction of t h e ion-exchange sites participates in the process of sodium retention. T h e HAP grains are of irregular shapes, which increases the flow resistance of the sorbent bed. Finally, the common procedures of HAP synthesis yield rather low fractions of the grains of the size appropriate for column operation. In order t o improve some of the properties of the sorbent, crystalline H A P was powdered and implanted into a matrix of a n ion-exchanger resin. A new composite ion exchanger has been thus obtained.
EXPERIMENTAL SECTION Crystalline HAP, obtained in the way described in ref 1,was powdered to grains of dimensions below 0.03 mm and then added in a calculated proportion to a viscous reaction mixture of sulfonated phenol with formaldehyde, commonly used in synthesizing polycondensation resins ( 4 ) . The resulting suspension was dispersed in Apiezon oil heated up to 90 OC. Small drops of this suspension, formed as a result of vigorous stirring, hardened within a couple of minutes. Spherical beads of the composite sorbent obtained that way were then separated from oil, degreased, and dried ( 5 ) . Retention of metal ions on the composite ion exchanger was studied under dynamic conditions from 8 M HC1. The diameter of the column was 4 mm and the bed height was 50 mm, the flow rate being 0.75 cm3/min. The following radionuclides, either supplied by the Isotope Production and Reactor Centre at Swierk near Warsaw or obtained by neutron irradiation of spectrally pure compounds, were used as radiotracers: 22Na,24Na,‘6As, lQSAu, lL5Cd,‘Wu, 59Fe, ‘%Hg, lL41n,42K,”Mn, *Tc, and ffiZn.A Ge(Li) detector (Schlumberger, active volume of 70 cm3, resolution of 3.1 keV for the 6oCo1332-keV peak), coupled to a 4096-channel pulse height analyzer Didac-4000 (Intertechnique) was used. Distribution coefficients of sodium ions were measured in batch experiments. Retention capacities of the sorbents were determined under dynamic conditions by passing a Na+ (1.5 mg/cm3) solution in 5 M HC1 through standard columns filled with 0.5 g of each
Table I. Some Properties of P u r e Crystalline HAP and the Composite Ion Exchanger Containing 60% HAP pure HAP
parameter grain shape grain size (diameter), mm distribution coeff of Na+ in 5 M HCl, cm3/g retention capacity for Na+, mg/g adsorption rate (tl12),min flow resistance resistance to: 5-8 M HCI 5-7 M HNOB
composite HAP
irregular spherical (beads) 0.1-0.3 0.1-0.3 3 x 102 2 x 103 29 4 high low0 low
23 3 low
high lowb
Peptization. The material slowly decays because of oxidation of the matrix.
Table 11. Elution of Sodium and Some Other Elements with 8 N HCl Solution from the Bed of HAP-Composite Ion Exc hangeru
element
% re1 content of the elements in the effluent 0-15 cm3 0-30 cm3
Na As Au Cd cu Fe Hg In K Mn Tc Zn
0
0
43.4 95.0 100 94.8 100 96.9 98.3 94.2 100 100 100
49.1 98.5 100 95.0 100 96.9 98.3 100 100 100 100
“Column diameter, 4 mm; bed height, 50 mm; diameter of beads, 0.1-0.3 mm; flow rate, 0.75 cm3/min; room temperature. sorbent studied, a t a rate of 0.3 cm3/min.
RESULTS Spherical beads of the composite ion exchanger containing 60% HAP in a phenolsulfonic-formaldehyde matrix, 0.05-0.5 mm in diameter, were synthesized. The fraction of dimensions from 0.1 to 0.3 m m was selected for the experiments (Figure 1). High yield of this fraction (over 50%) was attained; moreover, the granulation can easily be controlled in a broad range. The beads are of good mechanical stability comparable t o that of ion-exchange resins. T h e comparison of some properties of crystalline and composite HAP is given in Table I. It is noteworthy that the composite ion exchanger con-
0003-2700/87/0359-1737$01.50/00 1987 American Chemical Society
1738 * ANALYTICAL CHEMISTRY. VOL. 59. NO. 13. JULY 1. 1987
Table 111. Results of Cu and Mn Determination in Standard Reference Biological Materials std material
bovine liver. NBS 1577
analyt result
C" content: mean value
172
Mn content,'
pglg
recommended value analyt result
184
173
193 + 10
9.4
pg/g
mean value recommended value 9.3
10.3
1.0
8.9
rye flour, IAEA V-8
.Dry weight.
7-
*re taining
1. Beads (0.1-0.3 mm) of the Composite ion exchanger cow 60% HAP in phenolsulfonic~formaldehydematrix.
taining a bare 60% of the active sorbent (HAP) has a higher distribution coefficient for Na+ than the pure crystalline material. Also the retention capacity of the composite ion exchanger, when related to the content of the active sorbent, is greater than that of the pure crystalline HAP. Both observations can be explained assuming an increase of the number of active sites available for sodium ions in the composite material, obviously caused by reducing the sizes of the implanted HAP grains when compared to the pure HAP crystals. Improved kinetics of the ion exchange and decreased flow resistance of the composite sorbent make it possible to increase the flow rate of the effluent and reduce the time of the analysis. Due t o the increased resistance of the composite material t o hydrochloric acid, the HCI solutions of higher concentration can be used, decreasing the retention of some other elements of analytical interest. Examination of the retention of a number of metal ions often determined in biological samples (Table 11) shows that none of the elements tested, except arsenic, is retained on the HAP-composite sorbent from 8 M HCI (also selenium and tungsten are partly retained under these conditions (6)).while the retention of sodium-24 is quantitative, even a t 50 bed volumes of the effluent. This makes it possible to use the HAP-composite ion exchanger for removing from neu-
tron-activated biological samples more efficiently than pure crystalline HAP. The analytical application of the composite sorbent can be illustrated by the results of the determination of copper and manganese in two standard reference biological materials specified in Table 111. The irradiated samples (36-100 mg) were decomposed under heating in the mixture of HNO, and HClO. and then repeatedly evaporated to dryness with 8 M HCI. The residue was dissolved in a small amount of 8 M HC1 and the solution obtained was transferred into a column filled with the composite ion exchanger. The elution was carried out with 15 cm3 of 8 M HCI. Sodium-24 was completely retained on the sorbent bed, while copper and manganese quantitatively passed to the effluent. The results of the determination of both elements do agree with the recommended values (Table 111). The above procedure can be used as well to determine other nonvolatile elements not retainable on the composite ion exchanger from hydrochloric acid solutions. The composite sorhent can hardly be used in nitric acid solutions, not only due to worse selectivity of sodium separation but also because uf poor resistance of the phenolsulfonic-formaldehyde matrix to the oxidizing medium (Table I). I t is worth mentioning that also other inorganic ion exchangers of both analytical and technological interest, exhibiting poor mechanical stability but resistant to more concentrated solutions of sulfuric acid, can be transformed into stable beads of the composite sorbents (5, 7). Registry No. *"a. 13982-04-2;Sb20S,1314-60-9.
LITERATURE CITED (1) Girardi. F.; Sabbioni. E. J . RadimmI. Chem. 1968. 1 . 169-178 12) Amman. K.: Knkhel. A. Microchim. Acla 1984. 385-391. (3) Abe. M: In' Inorgank Ion Exch4nge Materials': Ckarifkld. A.. Ed.: CRS Press: Boca Ralon. FL. 1982: Chapter 6. p 226. (4) Rabek. T. 1. Teorefyczmpodrtawy synlazy polie~knoli6wi wmbnlsczy/onowych: PWN: Warszawa. 1960; p 354. (5) Narbun. J.: BartoL. 0.: Bilewic~.A,: Szeglawrki. 2. European Patent Appl 661 11963.4. 1986. (6) KuCera. J.. Nwcbar Research Inrliiute. be?. CzechosIovakia. persoml Communication. 1986. (7) Narbun. J.; SiwWrki. J.: BartoL. 8.: Bilewicz. A. J . Radiaaml. Nud. Chem. 1986, 101. 41-49.
RECEIWD for review November 14,1986. Accepted February 2, 1987. The work was supported hy the Central Research Programme C P B P 01.09.
