Partition of radionuclides in aqueous liquid-liquid systems allows speciation of bioinorganic forms under nondenaturing conditions. From the fresh pasteurized skim bovine milk spiked with respective radionuclides and agitated with 4% w/w water solution of apple pectin, about 80% of cesium, 22% of strontium and less than 1.5% of europium is recovered with the pectin, phase at an initial milk — pectin volume ratio of 73. This recovery fraction is proportional to the abundance of radionuclides in milk serum. No protein bound fraction of strontium extractable by Aerosol OT in isooctane was obtained. More than 3-fold preconcentration of strontium and europium radionuclides in milk is achieved after 10–15 min membraneless osmosis with pectin phase.
Aqueous two-phase systems allow partition of metal ions in nondenaturing conditions. From the fresh skim bovine milk spiked
with212Pb and agitated with 4% water solution of apple pectin (degree of esterification-70%), less than 2.3% is recovered to the
pectin phase and in the case of pasteurized milk less than 3.0%. Complexation with chelate forming agents was studied. Aminoacids
as glycine, alanine and histidine do not exert influence on the yield, but the recovery in the pectin phase was 22% for cysteine,
and 80% in the case of EdtacalTM (calcium salt of ethylenediaminetetraacetic acid). The retention of lead in milk phase is extraordinarily high as compared
to strontium and corresponds to the behavior of trivalent ions.
Speciation of fission products (90Sr,99Tc,137Cs and152Eu) in raw cow milk was studied using the high-performance size exclusion radiochromatography (HP-SERC) by Biosep-SEC-S® column
(Phenomenex, USA). The separation fraction were identified by a UV detector (280 nm) and a scintillation radiodetector. The
mobile phase was Jenness-Koops buffer that simulated milk serum. Radiocesium was present only in non-protein fractions. The
non-protein fractions complexed 17% of technetium and 57% of strontium. About 32% of strontium and 24% of europium were bound
on the high molecular weight proteins (micellar casein). Low molecular weight proteins bound about 11% of strontium and 76%
of europium. Non-size effects play a dominant role at HPSERC speciation of technetium, 83% of which follow the lightest fractions
Binding of added strontium by milk proteins under native conditions was investigated using pectin of various degrees of esterification. The partition of strontium, as well as cesium and europium, in aqueous two-phase milk-pectin system, is discussed in terms of membraneless dialysis and described by Donnan equilibria, and compared with the distribution between cation exchanger and milk, artificial milk serum, or pectin solutions. When going from pectin with a degree of esterification D.E.=93.2 to 61.4, the distribution of strontium decreases for about 40% in favor of pectin phase and this was explained by a relatively lower degree of dissociation of free carboxyle groups of pectin. The low-molecular fraction of added strontium in milk was assessed from Dowex 50×8 sorption data to be 31%, and that of cesium and europium 58% and 40%, respectively. However, distribution ratio of strontium and europium in milk/pectin system is much higher than it would correspond to the ion exchanger adsorption data.
Authors:P. Rajec, P. Gerhart, F. Macášek, I. Shaban, and P. Bartoš
The high-performance size-exclusion chromatography (HPSEC) and radiochromatography (HPSERC) was used for the identification
of radiocesium and radiostrontium interaction with humic acid. It was found that the behavior of humic acid on size-exclusion
chromatography is sensitive to the salt concentration and pH of the mobile phase. At lower ionic strength and in acidic region
of pH, the Aldrich humic acid exhibited three main fraction within the ranges >760 kDa, 25–100 kDa and <5 kDa. Radiocesium
was found in the low-molecular fractions (<1 kDa) of humic acids but radiostrontium interacts preferably with the fractions
of humic acid of molecular weight within the range 2–5 kDa.
Authors:F. Macášek, P. Gerhart, A. Malovíková, and A. Čelková
Partition of native sodium, potassium, magnesium, calcium and radioisotopes of cesium, strontium and curopium was investigated in the aqueous liquid-liquid systems formed after agitation of fresh pasteurized skim bovine milk with 4% w/w water solution of pectin of various degree of esterification (60–93%). The partition of the ions in the membraneless dialysis was described by Donnan equilibria and ion-exchange in the macro- and microheterogenous systems and, within uncertainty of results, does not depend on the degree of esterification. Strong negative non-ideality of Sr and Eu in milk phase is attributed to binding with proteins, casein particles in particular, and complexation with low molecular ligands. Separation factor =D(Sr)/D(Ca) is 0.70±0.06, in favor of strontium concentration in pectin phase. While >96% of cesium is diffusible to pectin phase, only 43–56% (depending on physico-chemical model of dialysis) of strontium behaves in that way, and in original milk phase the percent of strontium cationic form may be as low as 13%.