Calcium isotope fractionation in liquid chromatography with crown ether resins

Figures & data

Table 1. Experimental conditions and results other than isotopic data.

Run No.	Resin	Temp./°C	HCl concn. mol dm^−3	Ca^2 + ion concn. of the feed/mol dm^−3	Resin column height/cm	Flow rate/cm^3 h^−1	V 1/2/cm^3	Q/mmol	Q/Vr /mmol cm^−3
Ca18-1	B18C6	50	0.0	0.0513	193.0	6.2	83.8	0	0
Ca18-2		50	9.0	0.0480	193.0	6.0	131.0	2.27	0.172
Ca18-3		50	10.5	0.0476	193.0	5.7	161.4	3.70	0.280
Ca18-4		50	12.0	0.0466	193.0	6.0	217.8	6.24	0.473
Ca18-5		40	9.0	0.0468	193.0	6.0	140.1	2.59	0.196
Ca18-6		25	9.0	0.0478	193.0	6.0	150.4	3.18	0.242
Ca18-7		10	9.0	0.0481	193.0	5.9	160.2	3.67	0.279
Ca18-8		50	9.0	0.0474	488.5	5.9	331.2	5.65	0.169
Ca18-9		40	9.0	0.0470	488.5	5.9	348.1	6.39	0.192
Ca18-10		25	9.0	0.0476	488.5	6.0	379.0	7.94	0.238
Ca15-1	B15C5	50	4.5	0.0475	492.8	6.2	196.6	0	0
Ca15-2		50	10.5	0.0484	491.0	5.9	218.8	1.73	0.033
Ca15-3		50	12.0	0.0490	495.8	5.8	237.6	2.13	0.039

Figure 1. Plots of K _d as a function of HCl concentration in the feed solution at Ca²⁺ ion concentration of 0.05 mol dm⁻³. □, B18C6 resin at 25°C; ▪, B18C6 resin at 40°C; ○, B15C5 resin at 25°C; •, B15C5 resin at 40°C.

Figure 2. Plots of K _d as a function of Ca²⁺ ion concentration in the feed solution at a given HCl concentration at 25°C. □, B18C6 resin at HCl concentration of 9 mol dm⁻³; ▪, B18C6 resin at HCl concentration of 12 mol dm⁻³; ○, B15C5 resin at HCl concentration of 9 mol dm⁻³; •, B15C5 resin at HCl concentration of 12 mol dm⁻³.

Figure 3. Chromatograms with the benzo-18-crown-6 ether (B18C6) resin with varying HCl concentration. —□—, Run Ca18-1; —•—, Run Ca18-2; —○—, Run Ca18-3; —▴—, Run Ca18-4.

Figure 4. Chromatograms with the benzo-18-crown-6 ether (B18C6) resin at different temperatures and at different resin bed heights. —▵—, Run Ca18-2; —•—, Run Ca18-5; —□—, Run Ca18-6; —▾—, Run Ca18-7; —▴ — Run Ca18-8; —○—; Run Ca18-9; —▪—, Run Ca18-10.

Figure 5. Chromatograms with the benzo-15-crown-5 ether(B15C5) resin. —□—, Run Ca15-1; —○—, Run Ca15-2; —▴—, Run Ca15-3.

Figure 6. Chromatogram and LEF profiles of Run Ca18-8. ▪, ⁴²Ca/⁴⁰Ca isotopic pair; ○, ⁴³Ca/⁴⁰Ca isotopic pair; □, ⁴⁴Ca/⁴⁰Ca isotopic pair; •, ⁴⁸Ca/⁴⁰Ca isotopic pair.

Figure 9. Chromatogram and LEF profiles of Run Ca15-2. ▪, ⁴²Ca/⁴⁰Ca isotopic pair; ○, ⁴³Ca/⁴⁰Ca isotopic pair; □, ⁴⁴Ca/⁴⁰Ca isotopic pair; •, ⁴⁸Ca/⁴⁰Ca isotopic pair.

Figure 8. Chromatogram and LEF profiles of Run Ca18-10. ▪, ⁴²Ca/⁴⁰Ca isotopic pair; ○, ⁴³Ca/⁴⁰Ca isotopic pair; □, ⁴⁴Ca/⁴⁰Ca isotopic pair; •, ⁴⁸Ca/⁴⁰Ca isotopic pair.

Figure 7. Chromatogram and LEF profiles of Run Ca18-9. ▪, ⁴²Ca/⁴⁰Ca isotopic pair; ○, ⁴³Ca/⁴⁰Ca isotopic pair; □, ⁴⁴Ca/⁴⁰Ca isotopic pair; •, ⁴⁸Ca/⁴⁰Ca isotopic pair.

Table 2. Fractionation coefficients obtained in this work and in some previous chromatographic works.

Adsorbent	Resin type	Run No.	Temp./°C	HCl concn./mol dm^−3	ε/10^−3				ε/ΔM/10^−3				References
					^42Ca/^40Ca	^43Ca/^40Ca	^44Ca/^40Ca	^48Ca/^40Ca	^42Ca/^40Ca	^43Ca/^40Ca	^44Ca/^40Ca	^48Ca/^40Ca
Crown ether	B18C6	Ca18-2	50	9	0.9 ± 0.2	3.2 ± 1.5	2.7 ± 0.3	3.6 ± 1.2	0.43	1.04	0.68	0.45	This work
		Ca18-3	50	10.5	1.2 ± 0.6	2.4 ± 0.1	1.9 ± 0.5	4.3 ± 0.3	0.61	0.79	0.47	0.54
		Ca18-4	50	12	0.9 ± 0.2	1.1 ± 0.2	1.6 ± 0.2	2.8 ± 0.2	0.47	0.38	0.40	0.35
		Ca18-5	40	9	1.3 ± 0.5	3.0 ± 0.9	2.4 ± 0.3	6.0 ± 1.0	0.68	0.99	0.61	0.76
		Ca18-6	25	9	1.1 ± 0.2	2.4 ± 0.7	2.4 ± 0.2	4.3 ± 0.5	0.57	0.80	0.60	0.54
		Ca18-7	10	9	1.3 ± 0.1	1.9 ± 0.4	2.6 ± 0.2	4.4 ± 0.5	0.67	0.64	0.66	0.55
		Ca18-8	50	9	1.4 ± 0.5	1.3 ± 0.1	2.6 ± 0.3	4.0 ± 0.1	0.69	0.45	0.64	0.50
		Ca18-9	40	9	1.3 ± 0.1	2.2 ± 0.4	2.1 ± 0.6	4.0 ± 1.0	0.63	0.75	0.54	0.50
		Ca18-10	25	9	1.4 ± 0.1	2.1 ± 0.4	2.2 ± 0.2	4.2 ± 0.9	0.68	0.69	0.56	0.53
	B15C5	Ca15-2	50	10.5	0.26 ± 0.23	–	0.81 ± 0.38	–	0.13	–	0.20	–
		Ca15-3	50	12	0.18 ± 0.38	0.20 ± 0.21	0.40 ± 0.22	0.72 ± 0.26	0.088	0.066	0.099	0.089
	B18C6		35	9				3.1					[12]
	B18C6		27	9				1.9					[11]
	18-crown-6		20				1.7–2.5						[10]
Cryptand	[2B.2.2]		20				5.7–7.5	10.4–12.9					[7,8]
Ion exchanger	Strongly acidic		25		0.041	0.047	0.08	0.18					[5]
	(−SO3 ^−H^+)		25		0.11	0.16	0.21	0.37
			25		0.05	0.067	0.096	0.16
	(−SO3 ^−H^+)						1.1	1.8					[6]

Table 3. Comparison of energies of Ca species.

Entry	Ca species	Energy/kJ mol^−1	Difference
			Entry	Energy/kJ mol^−1
1	[Ca^2+(H2O)6](H2O)	−3182205.5	1–2	−17.9
2	[Ca^2+(H2O)7]	−3182187.5
3	[Ca^2+(H2O)6Cl^−]	−4190773.2	3–4	−12.2
4	[Ca^2+(H2O)5Cl^−](H2O)	−4190761.0
5	[B18C6 + CaCl2] (I)	−7018529.1	5–6	54.8
6	[B18C6 + CaCl2] (II)	−7018583.9
7	[B15C5 + CaCl2] (I)	−6614801.7	7–8	−8.6
8	[B15C5 + CaCl2] (II)	−6614793.1

Figure 10. Three-isotope plot of Run Ca18-8. ○, x = 43; □, x = 44; •, x = 48.

Figure 11. The optimized structures of (a) [Ca²⁺(H₂O)₆] and (b) [Ca²⁺(H₂O)₆Cl⁻].

Figure 12. The optimized structures of (a) [B18C6 + CaCl₂], (b) [B18C6 + CaCl₂ + HCl] and (c) [B18C6 + CaCl₂ + 2HCl].

Figure 13. The optimized structures of (a) [B15C5 + CaCl₂], (b) [B15C5 + CaCl₂ + HCl] and (c) [B15C5 + CaCl₂ + 2HCl].

Table 4. The values of the reduced partition function ratios for the ⁴⁸Ca/⁴⁰Ca isotopic pair at 50°C.

Phase	Species	rpfr for ^48Ca/^40Ca
Solution	Ca^2+(H 2 O)6	1.02522
	Ca^2+(H 2 O)7	1.02417
	Ca^2+(H 2 O)6Cl^−	1.02325
Crown ether (B18C6)	B18C6 + CaCl2	1.01751
	B18C6 + CaCl2 + H2O	1.01706
	B18C6 + CaCl2 + HCl	1.01713
	B18C6 + CaCl2 + 2HCl	1.01691
Crown ether (B15C5)	B15C5 + CaCl2	1.01816
	B15C5 + CaCl2 + HCl	1.01845
	B15C5 + CaCl2 + 2HCl	1.01925
	B15C5 + CaCl2 + 2HCl + H2O	1.01888

Fujii , Y. , Nomura , M. , Kaneshiki , T. , Sakuma , Y. , Suzuki , T. , Umehara , S. and Kishimoto , T. 2010 . Mass dependence of calcium isotope fractionations in crown-ether resin chromatography . Isotopes Environ. Health Stud , 46 : 233 – 241 .

 PubMed Web of Science ®Google Scholar

Hayasaka , K. , Kaneshiki , T. , Nomura , M. , Suzuki , T. and Fujii , Y. 2008 . Calcium ion selectivity and isotope effects studied by using bwnzo–18-crown-6 resins . Prog. Nucl. Energy , 50 : 510 – 513 .

 Web of Science ®Google Scholar

Jepson , B.E. 1992 . Calcium isotope separation by chemical exchange with polymer-bound crown compound . Bull. Res. Lab. Nucl. Reactors Special Issue , 1 : 307 – 312 .

 Google Scholar

Heumann , K.G. and Schiefer , H. 1980 . Calcium isotope separation on an exchange resin having cryptand anchor groups . Angew. Chem. Int. Ed. Engl , 19 : 406 – 407 .

 Web of Science ®Google Scholar

Heumann , K.G. , Schiefer , H.P. and Spiess , W. 1982 . “ Enrichment of heavy calcium isotopes by ion exchanger resins with cyclopolyethers as anchor groups, in ” . In Stable Isotopes Edited by: Schmidt , H.-L. , Förstel , H. and Heinzinger , K. 711 – 718 . Elsevier , , Amsterdam

 Google Scholar

Oi , T. , Morioka , N. , Ogino , H. , Kakihana , H. and Hosoe , M. 1993 . Fractionation of calcium isotopes in cation-exchange chromatography . Sep. Sci. Technol , 28 : 1971 – 1983 .

 Web of Science ®Google Scholar

Jepson , B.E. and Shochey , G.C. 1984 . Calcium hydroxide isotope effects in calcium isotope enrichment by ion exchange . Sep. Sci. Technol , 19 : 173 – 181 .

 Web of Science ®Google Scholar