An analytical technique of rare-earth elements (REE) in rock samples using a high-performance ion chromatography (HPIC) is described. The REE in rock samples were separated from other elements using a conventional ion-exchange column, and then measured by the HPIC. α-hydroxyisobutyric acid and Arsenazo III were used for eluants and a post-column reagent for the HPIC, respectively. The use of a high-resolution HPIC column enabled to analyze all fourteen REE without any interference from Y and other transition metals. The REE concentrations determined for twelve Geological Survey of Japan rock reference samples, having varied major element compositions, showed good agreement with the recommended values and the values recently obtained by inductively coupled plasma-mass spectrometry (ICP-MS). This HPIC technique provides an inexpensive means to obtain high-quality data of all fourteen REE in rock samples as small as <50 mg, and potential for wide geochemical applications as an alternative to ICP-MS. cisely and rapidly. However, the REE analysis using all these methods requires significantly large instrumental, running and maintenance costs. In addition, ICP-AES requires relatively large sample size (500 to 1000 mg) for precise REE determination and has difficulties in analyzing low levels of Pr, Tb and Tm (Walsh et al., 1981). INAA needs access to a nuclear reactor facilities for REE analysis, and is also generally unsuitable for the determination of Pr, Gd, Dy, Ho and Er (Barnes and Gorton, 1984). ID-TIMS is the most precise and accurate method for REE analysis, but not applicable to the determination of monoisotopic REE (Pr, Tb, Ho and Tm). Therefore the development of an alternative method that is capable of analyzing all REE in small amount of rock samples at a reasonable cost still has great signifi-
