Transition-metal ion analyses have been one of the most important research themes in the fields of not only analytical chemistry, but also environmental science and medicine. Absorption spectrophotometry, atomic absorption spectrophotometry, and inductivity coupled plasma are commonly used for detecting metal ions. Chemiluminescence (CL) has also received much attention as a detection method for metal ions, because CL detection features high sensitivity, a wide determinable range, inexpensive reagent and apparatus, and easy and rapid measurements. FIA, HPLC, and capillary electrophoresis (CE) equipped with CL detection have been shown to be useful analytical methods for metal ions.
1,2Recently, investigations for a micro total analysis system (µ-TAS) have given rise to significant analytical challenges. For example, CE integrated on a microchip (microchip CE) has been much studied. While many researchers have reported microchip CE using laser-induced fluorescence detection, we have developed microchip CE with CL detection. 3 Because CL detection does not require any light sourse or spectroscopes, the system is comparatively simple. We successfully analyzed a mixture of dansyl amino acids by the microchip CE-CL detection using a peroxyoxalate reagent.To the best of our knowledge, there has been no report concerning metal-ion analyses by means of microchip CE, except for Kutters' report. 4 They examined two model compounds, magnesium and calcium ions, by microchip CE using UV laser-induced fluorescence following complexation with 8-hydroxyquinoline-5-sulfonic acid. In the present study, we applied, for the first time, microchip CE-CL detection to the separation and detection of transition-metal ions. We used luminol reagent and the same microchip as previously reported.
ExperimentalA schematic layout of the microchip is illustrated in Fig. 1. 3 The microchip, made of quartz, was fabricated at Technology Research Laboratory of Shimadzu Corporation. It had the simplest design: four reservoirs (R1 -R4), only two main channels (sample load channel (from R1 to R2) and separation channel (from R3 to R4), and a cross-shaped injector. The channels were 20 mm deep and 50 mm wide, except for the large part. The channel length from the intersection to R4 (which corresponded to the effective separation length) was 33.0 mm.All chemicals were of analytical grade and were used without further purification. Ion-exchanged water was distilled before use. A 25-mM CH3COOH-CH3COONa (pH 4.5) buffer solution including 6 mM 2-hydroxyisobutyric acid was prepared. Metal ions (Co(II), Cu(II), Ni(II), and Fe(III); chlorides) were dissolved with the buffer solution to give sample solutions. A solution prepared by dissolving luminol (1 mM) in the buffer solution was used as a migration buffer. A H2O2 solution (0.05 mM H2O2 and pH 11.4) was prepared by mixing 0.5 mM H2O2, 25 mM CH3COOH, and 25 mM NaOH solutions with a volume ratio of 1:8:1. After the channels on the microchip were filled with the migration buffer, the sample solution was place...