Application of capillary electrophoresis for trace ion analysis in rain water†

Solving the problem due to transition metals' comigration during electrokinetic injection, the transient isotachophoresis (ITP) procedure was developed to preconcentrate and focus transition metals during electrokinetic injection. It was found to provide a suitable method for trace metals' preconcentration from rainwater at sub-μg/L level from buffer system consisting of 30 mM hydroxylamine hydrochloride, 0.1 mM 1,10-phenanthroline, 1% methanol, 15 mM ammonium chloride, and 0.08 M urea at pH=3.7. Trace metals as Cd²⁺, Zn²⁺, Cu²⁺, Co²⁺, and Fe²⁺ (total Fe determined as Fe²⁺) are determined with working range from 0.5–80 μg/L, repeatability less than 7%, and detection limits from 0.1 to 0.5 μg/L under optimized operation conditions as follows: Injection at 3 kV for 40 s prior to CE run at +15 kV in buffer system developed and with 0.4 mM tetrabutyl ammonium bromide added to rain sample as terminating ion. Leading and terminating ion effect, buffer additive, and operation conditions on performance of ITP procedure were investigated. Procedure developed was applied for trace metals' determination in rain water collected in Hong Kong. It provides fast, efficient, and economic method determining transition metals in rain sample down to sub-μg/L level, reducing sample pretreatment time and eliminating off-column preconcentration steps often leading to contamination problems for transition metals determination at μg/L level. © 2000 John Wiley & Sons, Inc. J Micro Sep 12: 337–344, 2000