Calcium isotope fractionation in liquid chromatography with crown ether resin in methanol medium

Abstract

Breakthrough mode liquid chromatography was employed to investigate calcium (Ca) isotope fractionation in methanol medium. Highly porous silica beads, the inner pores of which were embedded with a benzo-18-crown-6 ether resin, were used as column packing material. Enrichment of heavier isotopes of Ca was observed in the frontal part of the respective Ca chromatograms. The values of the isotope fractionation coefficient (ϵ) were in the order of 10(-3) at 25 °C. Use of methanol as solvent has little advantage over the aqueous system as far as the values of ϵ are concerned. However, a substantial improvement was observed concerning the adsorption capacity of the crown ether resin for Ca ions. Molecular orbital calculations supported the present isotopic results in a qualitative fashion.

Calcium isotope fractionation in liquid chromatography with benzo-18-crown-6 resin in aqueous hydrobromic acid medium

“…The findings in Table 2 and Figures 2-5 may be summarized as follows: were obtained with the B18C6 resin; they are on the same order as those of the previous studies with the same resin [17][18][19][20], and larger than those of the studies with ion exchange resins [3,4] and with the B15C5 resin (benzo-15-crown-5 ether resin synthesized in the inner pores of highly porous silica beads [11]) [19]. (3) The ε value seems, admittedly roughly, nearly proportional to the isotopic mass difference, M. In other words, the ε/ M value is nearly constant in a given run.…”

“…The smallness of the deviation of the experimental slope from the theoretical one supports that the isotope effects in the present systems are normal mass-dependent ones. We note, however, that in some experiments of our present and previous papers [19,20], the ε/ M value is found to be larger for the 43 Ca/ 40 Ca isotopic pair than for the other pairs beyond experimental uncertainties. .…”

“…The B18C6 resin, embedded in the inner pores of highly porous silica beads (diameter: 40-60 μm), is a copolymer of phenol and monobenzo-18-crown-6 [17]. In our previous papers [19,20], we examined the Ca isotope effects in breakthrough-mode liquid chromatography with the B18C6 resin in aqueous and methanol hydrochloric acid (HCl) media. We found that (1) the lighter isotopes of Ca are preferentially fractionated to the B18C6 resin phase rather than the solution phase; (2) a higher concentration of HCl resulted in smaller Ca isotope effects; (3) observed isotope effects 642 T. Sato and T. Oi are mass-dependent; and (4) the use of methanol as solvent has little advantage over the aqueous system as far as the magnitude of Ca isotope effects is concerned, but a substantial improvement was observed concerning the adsorption capacity of the resin for Ca 2 + ions.…”

Sol–Gel Derived Benzo-Crown Ether-Functionalized Silica Gel for Selective Adsorption of Ca2+ Ions

“…Lauth and Gramain reported that the performance of the cation separation strongly depends on the chemical structure of the bound crown ether, and on the preparation process and the choice of the silica support . Recently, a porous silica bead embedded with benzo-18-crown-6 ether was used for the selective separation of Ca 2+ ions. , …”

In-situ sampling of available calcium using diffusive gradients in thin-films technique based on benzo-crown ether-functionalised silica as the binding agent

“…Crown ethers are a class of compound that can form very stable molecular ensembles or complexes with alkaline and alkaline earth metals (Pedersen 1967;Stover 1984;Høiland et al 1979). The previous literature has reported that benzo-18crown-6 ether has been successfully used for the selective separation of Ca 2þ relative to other alkali metal cations (Capel-Cuevas et al 2009;Okumura et al 2015;Nemoto et al 2013). The PES membrane is an excellent performance material for membrane separation due to its superior mechanical and chemical properties (Liu et al 2011).…”