Toward a Fully Integrated Positive-Pressure Driven Microfabricated Liquid Analyzer

A versatile integrated analyzer with a flow-programmed injection strategy and multiwavelength detection is described with applications toward sampling, flow injection analysis, and capillary separations. Continuous near-real-time sampling is a major benefit of the flow-programmed injection technique. Injection volumes ranging from 250 pL to several microliters were made without electrophoretic flow. Multiwavelength grating light reflection spectroscopy (GLRS) and transmission absorbance spectroscopy were performed simultaneously in a detection volume of 150 pL. The utility of these detection methods for refractive index (RI) and absorbance detection in capillary channels is demonstrated through analysis of salt, indicator, and dyes. GLRS is a unique, selective, and path-length-independent technique for probing RI, absorbance, and other optical properties. A limit of detection (LOD) of 170 microM was achieved for GLRS interferometric detection of FD&C Red #3, which corresponded to 2.6 fmol of analyte in the 150-pL detection volume. A LOD of 2 mM for phosphate buffer, or 3 fmol in the 150-pL detection volume will also be demonstrated. A siloxane coating on the GLRS grating was employed as a sensing layer to probe interactions between the sample and stationary phase. The combined GLRS interferometric response provided insight into both optical and chromatographic properties of samples. Open tubular capillary liquid chromatography with multidimensional multiwavelength detection is demonstrated for the analysis of three food dyes. Separation efficiency, N, of 16,000 was achieved for an unretained dye peak eluting at 12 min. Integration of novel sampling and detection schemes makes this a broadly applicable liquid analyzer.