Anal. Chem. 2000, 72, 2595-2602
Quantification of Lanthanides in Rocks Using Succinic Acid-Derivatized Sorbents for On-Line SPE-RP-Ion-Pair HPLC Michael R. Buchmeiser,*,† Gernot Seeber,† and Richard Tessadri‡ Contribution from the Institute of Analytical Chemistry and Radiochemistry, Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria
The use of new poly(norbornene-block-7-oxanorborn-2ene-5,6-dicarboxylic acid)-coated silica-based sorbents as well as of beaded polymers based on poly(norborn-2-ene5,6-dicarboxylic acid-co-1,4,4a,5,8,8a-hexahydro-1,4,5,8exo-endo-dimethanonaphthalene) for the on-line preconcentration of lanthanides from rock digests and their subsequent RP-ion-pair HPLC separation is described. Block co-polymers of norborn-2-ene and 7-oxanorborn2-ene-5,6-dicarboxylate used for coating were prepared by ring-opening metathesis polymerization (ROMP) and poly(norborn-2-ene-5,6-dicarboxylic acid-co-1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo-endo-dimethanonaphthalene)based polymer beads were prepared by ring-opening metathesis precipitation polymerization. Both types of sorbents exhibit an extraordinarily good pH stability, are hydrophilic and therefore easily wetable by water alone, and show high extraction efficiencies for lanthanides within a pH of 3.5-5.5. The rare earth element (REE) content in the investigated rocks varied over 3 orders of magnitude (0.19-108 µg/g). REE concentrations prior to enrichment were typically in the range of 1-25 ng/ mL; the total amount of each REE sorbed onto the precolumn was in the range of 8-270 ng. Extraction selectivities of the sorbent may be enhanced by adding 5-sulfosalicylic acid as a masking agent for iron and aluminum as well as methanol as an inhibitor for the precipitation of o-silicic acid. Gradient elution of the lanthanides from the precolumn and their subsequent separation on a RP-C18 column was achieved using hydroxyisobutyric acid (HIBA) and sodium octanesulfonate. Depending on the actual concentration of the lanthanides in the digests and in order to suppress interfering cations, UV detection was carried out with two different postderivatization reagents, 4-(2-pyridylazo)resorcinol (PAR) and arsenazo III. The high selectivity in enrichment as well as the complementary use of post-derivatization reagents allows the fast, quantitative, and highly reproducible quantification of REEs present in rocks by complete removal or suppression of all other interfering components. Thus, recoveries were found to be within a range of 97-103% for most REEs with relative standard deviations of 2-5%. Lanthanides are among the most important elements for elucidating igneous rock petrogenesis and for the interpretation 10.1021/ac991217i CCC: $19.00 Published on Web 04/29/2000
© 2000 American Chemical Society
of processes of metasomatism, ore formation, and rock alteration.1 In principle, rare earth elements (REEs) may be extracted from aqueous rock digests using solvent extraction. Xanthogenates2-4 or other designed ligands such as N,N′-dimethyl-N,N′-diphenyl3-oxapentanediamide,5 N,N′-bis(5-nitrosalicidene)-o-phenylenediamine,6 4-phenyl-4-benzoyl-5-isoxazolone,7 triphenylphosphine oxide,8 or 1-phenyl-3-methyl-4-benzoyl-5-pyrazone9 have been used. In the case of comparably low amounts of REEs (10 µg/g. In the case of GSR-1 granite, which possesses a Th content of 54 µg/g, it consequently influences the mean recovery value (112%) Analytical Chemistry, Vol. 72, No. 11, June 1, 2000
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as well as the relative standard deviations (RSDs ) 7%) for Ho (6). In GSR-3 basaltic rock, which shows a reduced Th content of only 6 µg/g, good recovery values of 98% with low RSDs (3%) were obtained for this element. Since Fe3+, Mn2+, Co2+, Ni2+, Zn2+, and Cu2+ do not react with arsenazo III, their influence on the recoveries of REEs may be ruled out by using this compound for post derivatization. CONCLUSIONS New and highly efficient sorbents based on poly(norborneneblock-7-oxanorborn-2-ene-5,6-dicarboxylic acid)-coated silica for the on-line SPE-HPLC of lanthanides have been developed. Extraction efficiencies are quantitative in a concentration range of at least 1-50 ng/mL. Generally, an extraction pH of 3.5-5.5 was found applicable. The materials are stable within a pH range of 0 to g12, and may be recycled many times. Recoveries for REEs were determined for two different types of rocks, which differed significantly both in their REE content and in the concentration of the major elements. While significant cocomplexation was observed for UO2+, Th4+, Al3+, Fe3+, and Cu2+, minor amounts of Mg2+, Ca2+, Ba2+, Mn2+, Cd2+, Co2+, Ni2+, and Zn2+ were sorbed onto the precolumn. Al3+ and Fe3+ may selectively be masked using 5-sulfosalicylic acid; Mg2+, Ca2+, and Ba2+ do not react with either of the two post-derivatization reagents employed. The influence of UO2+, Mn2+, Co2+, Cu2+, Ni2+, and Zn2+ may be eliminated using different post-derivatization reagents. Th4+ coelutes with Ho, leading to slightly elevated recovery and RSD values. The present system is the first that allows a fast, convenient, and highly reproducible quantification of REEs by a simple
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method. It is therefore believed to represent an attractive alternative to standard, time-consuming, preparative-scale ion-exchange off-line enrichment procedures. In the absence or in the presence of low concentrations (e5 µg/g rock) of interfering transition metal cations, the total analysis time for one run (including preconcentration) is less than 1 h. In the presence of higher concentrations of these transition metal ions, two runs with two different post-derivatization reagents have to be performed. Following the setup described in this contribution, the REE content of any granite or basaltic rock digest may accurately and conveniently be determined via on-line SPE-RP-ion-pair HPLC. ACKNOWLEDGMENT Financial support was provided by the Austrian National Science Foundation (FWF, Vienna, Austria, project number P-12963-GEN). SUPPORTING INFORMATION AVAILABLE Composition of GSR-1 granite and GSR-3 basalt. Complete data set for rock reference materials (IGGE Institute of Geophysical and Geochemical Prospecting, People’s Republic of China); data from lit.44 This material is available free of charge via the Internet at http://pubs.acs.org.
Received for review October 25, 1999. Accepted February 22, 2000. AC991217I
