Quantification of lanthanides in rocks using succinic acid-derivatized sorbents for on-line SPE-RP-ion-pair HPLC

The use of new poly(norbornene-block-7-oxanorborn-2-ene-5,6-dicarboxylic ac id)-coated silica-based sorbents as well as of beaded polymers based on pol y(norborn-2-ene-5, 6-dicarboxylic acid-co-1,4,4a,5,8,8a-hexahydro-1,4,5,8-e xo -endo-dimethanonaphthalene) for the on-line preconcentration of lanthani des from rock digests and their subsequent RP-ion-pair HPLC separation is d escribed. Block co-polymers of norborn-2-ene and 7-oxanorborn-2-ene-5,6-dic arboxylate used for coating were prepared by ring-opening metathesis polyme rization (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 wer e prepared by ring-opening metathesis precipitation polymerization. Both ty pes of sorbents exhibit an extraordinarily good pH stability, are hydrophil ic and therefore easily wetable by water alone, and show high extraction ef ficiencies 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 mu g/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 preco lumn 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-C-18 column was achieved using hydroxyi sobutyric acid (HIBA) and sodium octanesulfonate. Depending on the actual c oncentration of the lanthanides in the digests and in order to suppress int erfering cations, UV detection was carried out with two different post-deri vatization reagents, 4-(2-pyridylazo)resorcinol (PAR) and arsenate III. The high selectivity in enrichment as well as the complementary use of post-de rivatization reagents allows the fast, quantitative, and highly reproducibl e quantification of REEs present in rocks by complete removal or suppressio n of all other interfering components. Thus, recoveries were found to be wi thin a range of 97-103% for most REEs with relative standard deviations of 2-5%.