The use of single and multiple capillaries for the separation and analysis of complex chemical mixtures

The use of capillary array electrokinetic methods is developed for the separation of complex chemical mixtures. Various chromatographic conditions and capillary formats are explored for the purpose of achieving optimal separation information by taking advantage of the diverse selectivities of the different capillary columns, conditions, and formats.; Particular attention was devoted to the separation of a mixture of polycyclic aromatic hydrocarbons (PAHs) that have similar chemical structures. At first, the potential of capillary electrochromatography (CEC) was explored for the analysis of the neutral PAHs. An intracavity-doubled argon ion laser operating at 257 nm was used for laser-induced fluorescence (LIF) detection. This CEC-LIF approach combined the good selectivity of high performance liquid chromatography (HPLC) with the high efficiency of capillary electrophoresis (CE). All 16 PAHs could be resolved with detection limits ranging from 10−17 to 10−20 moles. Complete resolution, however, required multiple operating conditions. This fact brought up the needs of developing and implementing capillary separations in parallel—the concept of capillary array analysis.; The capillary array CEC separation of mixture of PAHs, nitrogen-containing aromatic compounds (NCAC) and extracts of creosote-contaminated soil samples was investigated. The CEC columns were all packed with the identical stationary phase but various mobile phase compositions were used. Multiple electrochromatograms were generated simultaneously with each capillary operating condition chosen to give unique information about the sample of interest. This approach led to a significant increase in chromatographic information as well as a significant reduction in analysis time. In essence, this approach takes the place of running a gradient separation by using a number of simultaneous isocratic separations. A computer-controlled scanning LIF experimental setup was utilized to perform high-sensitivity detection on each of the capillaries used.; The parallel capillary array approach was further improved to achieve additional chromatographic diversity by varying pseudostationary conditions in addition to mobile phase conditions. Its use was illustrated by applying it to separate and analyze the mixture of amino acids that had been derivatized with naphthalene-2,3-dicarboxaldehyde (NDA) so that they were fluorescent. The complete separation profile for 17 NDA-amino acids was obtained within 6 minutes by combining separation information available from different channels.