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Liquid chromatography (LC) is a powerful tool in trace metal analysisl-3, especially in cases where the available quantity of samples is strictly limited, e.g. clinical examination, air pollution monitoring, and quality control in the electronics industry. Although the current sensitivity is high, it is often limited by peak broadening due to the large elution volume used and slow mass-transfer kinetics. In fact, the LC column is an effective dilution device.4 A powerful alternative seems to be the micellar electrokinetic capillary chromatography (MECC) system in which the electroosmotic delivery of a mobile aqueous phase with a micellar pseudo-stationary phase is utilized; this system was first described by Terabe and coworkers.5-' In this type chromatography, an almost ideal plug-flow velocity profile of electroosmotic fluids and a micellar pseudo-stationary phase of colloidal dimension dispersed in a bulk aqueous phase provide extremely high theoretical plate numbers (more than 2X105 plates/60 cm, HETP=(2 4) μm).56 Excellent success of the MECC system has been demonstrated for the separation of phenols5, amino acids', B6 vitamers9, oligonucleotides10, and metal chelates11, as well as a theoretical bases for the separation processes presented.6,12,13 Although such extremely high efficiency of the MECC (sharpness of peaks) can undoubtedly afford an improvement of the spectrophotometric detection limits (D.L.), there is a possible disadvantage associated with the minute detector volume and short light path length. In the case of the oncolumn absorbance detection mode, the detector light path is as long as the diameter of the capillary used (typically 0.05 mm), which is by a factor of 1/200 shorter than that of ordinary 10 mm cells. Nonetheless, indeed, the very low detection limit on a mass basis (1.4 fmol f or the 4-(2-pyridylazo)resorcinolatoCr(III) chelate) has been suggested.ll An investigation has thus been conducted to assess the attainable D.L. of metals with the MECC-spectrophotometric detection system using water-soluble porphines as precolumn labeling agents, since they have enormous great molar absorption coefficients (E~ 7X105 cm 1 M-1) at the Soret absorption bands.14 Among the porphine analogs examined, aj3,y,S-tetrakis(4carboxyphenyl)porphine (TCPP) was found to be one of the most promising reagents for MECC application using a sodium dodecyl sulfate (SDS) micellar solution. The present work describes the first access to the subfemtomole detection of metal chelates in solution with a spectrophotometric means coupled with the MECC separation scheme without any preconcentration processes.

Micellar Electrokinetic Capillary Chromatography of Porphinato Chelates as a Spectrophotometric Approach to Sub-Femtomole Detection of Metal Chelates