Anal. Chem. 1996, 68, 1517-1520
Ion Chromatographic Separation of Rare-Earth Elements Using a Nitrilotriacetate-Type Chelating Resin as the Stationary Phase Yoshinori Inoue, Hiroki Kumagai,* and Yoshiko Shimomura
R&D, Yokogawa Analytical Systems Inc., 2-11-19 Naka-cho, Musashino-shi, Tokyo, 180 Japan Toshiro Yokoyama and Toshishige M. Suzuki
Tohoku National Industrial Research Institute, 4-2-1 Nigatake, Miyagino-ku, Sendai, 983 Japan
The chromatographic retention behavior of rare-earth elements (REEs) on a chelating resin having a nitrilotriacetate group (NTA gel) was evaluated. The capacity factors for a series of REEs on the NTA gel were in fairly good agreement (R2 ) 0.978) with the stability constants of the corresponding NTA complexes. The NTA gel was applied to the column stationary phase for the ion chromatographic separation of REE. A favorable separation of a series of REEs was achieved within 15 min using a gradient elution of nitric acid. The separated REE ions were detected using the postcolumn derivatization method with chlorophosphonazo III as a colorization reagent. The present chromatographic system, interfaced with inductively coupled plasma mass spectrometry, was applied for the simultaneous determination of 14 REEs.
Ion chromatography (IC) is an attractive procedures for the analysis of rare-earth elements (REEs). Typically, low-capacity cation exchange resins with sulfonic acid or carboxylic acid are used as the stationary phases, with aqueous solutions of complexing agents as the mobile phases. The separated REEs are most commonly determined using the postcolumn derivatization method. Recently, ICP-AES and ICPMS interfaced with ion chromatography have been applied to simultaneous and multielement analytical techniques for the determination of REEs.1,2 However, a large amount of organic reagent used as the mobile phase may cause spectral interferences due to molecular bands such as CO, CN, OH, or NH. In addition, the concentrated salt solutions tend to influence the nebulization efficiency due to the high viscosity. In the case of using ICPMS, the interferences due to polyatomic ions cause a serious problem.3,4 In contrast, when a selective ion exchange resin is used as the column stationary phase, a simple mineral acid may be used as the mobile phase. (1) Yoshida, K.; Haraguchi, H. Anal. Chem. 1984, 56, 2580. (2) Kawabata, K.; Kishi, Y.; Kawaguchi, O.; Watanabe, Y.; Inoue, Y. Anal. Chem. 1991, 63, 2137. (3) Vaughan, M.; Horlick, G. Appl. Spectrosc. 1986, 40, 434. (4) Tan, S. H.; Horlick, G. Appl. Spectrosc. 1986, 40, 445. 0003-2700/96/0368-1517$12.00/0
© 1996 American Chemical Society
Recently, selective polymer resins, including chelating resins and reagent-impregnated resins, have been applied to the stationary phase for the chromatographic separation of REEs.5-9 The selectivity of a chelating resin is attributed mainly to the nature of the immobilized ligand on the base matrix. We have introduced a lysine-NR,NR-diacetic acid into a fine polystyrene gel. The metal binding site, which is structurally similar to nitrilotriacetic acid, is apart from the bulky polymer matrix.10,11 The selectivity order of the chelating resin (NTA gel) for a series of REEs was evaluated, and a good correlation was obtained between the distribution coefficients and the corresponding stability constants of the NTA complexes.11 This result indicates that simple mineral acid may be used as the mobile phase for separating REEs on a NTA gel. In this study, a fine-particle hydrophilic polymer-based NTA gel was synthesized, and the retention behavior for REEs was evaluated. Furthermore, a simultaneous determination of a series of REEs was examined using ion chromatography, followed by the postcolumn derivatization method, as well as ICPMS.
EXPERIMENTAL SECTION Synthesis of the NTA Gel. The cross-linked glycidyl methacrylate gel (GMA gel) was obtained from Hitachi Chemical Co., Ltd. (Tokyo, Japan) as the base matrix. The GMA gel is a macroporous-type hydrophilic resin with a diameter of 10 µm. The procedure for introducing NTA into the base matrix was based on previous reports.10,11 The synthesis scheme is shown in Figure 1. The polymer beads (5 g) were added to an aqueous solution (100 mL) containing lysine-NR,NR-diacetic acid (25 mM). The mixture was adjusted to pH 11 and was then kept at 50 °C for 24 (5) Takeda, K.; Akiyama, M.; Kawakami, F.; Sasaki, M. Bull. Chem. Soc. Jpn. 1986, 59, 2225. (6) Wakui, Y.; Matsunaga, H.; Suzuki, T. M. Anal. Sci. 1989, 4, 325. (7) Kanesato, M.; Yokoyama, T.; Suzuki, T. M. Bull. Chem. Soc. Jpn. 1989, 62, 3451. (8) Kanesato, M.; Kooptarnond, K.; Suzuki, T. M. Chem. Lett. 1991, 1839. (9) Kobayashi, S.; Wakui, Y.; Kanesato, M.; Matsunaga, M.; Suzuki, T. M. Anal. Chim. Acta 1992, 262, 161. (10) Yokoyama, T.; Kanesato, M.; Kimura, T.; Suzuki, T. M. Chem. Lett. 1990, 693. (11) Yokoyama, T.; Asami, S.; Kanesato, M.; Suzuki, T. M. Chem. Lett. 1993, 383.
Analytical Chemistry, Vol. 68, No. 9, May 1, 1996 1517
Figure 1. Synthesis scheme of the NTA gel. Table 1. ICPMS Operating Conditions instrument rf forward power rf reflected power plasma gas flow auxiliary gas flow carrier gas flow sampling depth dwell time no. of scans
Model HP 4500 1.3 kW
