Study of chemical states of lanthanoid nitrate in solution by electrospray ionization and fast atom bombardment mass spectrometry

Abstract Lanthanoids (Ln) are used in batteries, magnets and various industrial materials. Due to wide applications and few resources, efficient methods for the recovery of Lns are required. In this study, the soluble states of Ln in aqueous and organic phases were directly observed by electrospray ionization mass spectrometry (ESI-MS). We used La(NO 3 ) 3 , Pr(NO 3 ) 3 , and Tb(NO 3 ) 3 as representatives of Ln in our studies. When La(NO 3 ) 3, and Tb(NO 3 ) 3 was dissolved in water at pH 4.7, [La 2 (NO 3 ) 3 (H 2 O) n ] 3+ ( n  = 0, 3) or [La 2 (NO 3 )(OH) 2 (H 2 O) m ] + (m = 9, 10), were observed. When La(NO 3 ) 3, Pr(NO 3 ) 3, and Tb(NO 3 ) 3 were dissolved at pH 1.8, [La 2 (NO 3 ) 3 (H 2 O) n ] 3+ ( n  = 0, 3, 6, 9), [Pr 2 (NO 3 )(OH) 2 (H2O) 7 ] 3+ , [Tb 2 (NO 3 )(OH) 2 (H 2 O) n ] 3+ ( n  = 6, 9, 12, 15, 18) were mainly observed. Particularly, in the Pr and Tb solutions, monomers generated were identified. By fast atom bombardment mass spectrometry, monomer of Ln was not observed but dimer with glycerin was observed. This indicated that monomer was sufficiently hydrated to be ionized by fast atomic bombardment mass spectrometry (FAB-MS). But dimer with glycerin was ionized due to less hydration by FAB-MS. On the other hand, when La, Pr, and Tb were extracted with TOPO in hexane solution at pH 1.8, [Ln(NO 3 ) 2 -3TOPO] + , [Ln(NO 3 ) 2 -4TOPO] + , and the monomers and dimers of TOPO (Ln = La, Pr, and Tb) were observed. This ESI-MS method could be useful for identifying chemical species in both aqueous and organic solutions.