Determination of rare-earth elements in rocks by liquid chromatography

Abstract

A high-performance liquid chromatographic (HPLC) procedure has been developed and tested for the determination of rare-earth elements (REE) in rocks. The REE in a ∼50-mg rock sample were first separated as a group on a 3-ml bed of cation-exchange resin with a combination of oxalic and nitric acids, and then separated from one another by dynamic ion-exchange HPLC on a reversed-phase column. Eluted REE were monitored by visible spectrophotometry at 658 nm after an on-line postcolumn reaction with Arsenazo III. Detection limits for the HPLC procedure were in the range of 0.1–0.5 ng (∼0.01 μmg g −1 for a 50-mg rock sample) and repeatabilities were ±0.5–2.0% for samples with concentrations > 10 × detection limit. The REE results obtained for a series of rock standards showed good agreement with recommended values and values obtained by isotope-dilution techniques. For the nine rocks studied the concentrations of the REE covered the range of 0.09–470 μg g −1, and the average value of the ratio, (HPLC result)/(reference result), was 0.983. The average % r.s.d. value of this ratio for individual REE was 4.1, which is the value expected for the comparison of two analytical techniques each having a r.s.d. of 2.9%. Rocks used for this evaluation included the international rock standards BCR-1, W-2, DR-N and BR, and a granite, a komatiite, a mid-ocean ridge basalt (MORB) basalt, a Hawaii Kilauea basalt and a begalith.