Microfluidic flow-injection thermal-lens microscopy for high-throughput and sensitive analysis of sub-mu L samples

摘要

An analytical method combining microfluidic flow-injection analysis (mu FIA) with thermal-lens microscopy (TLM) was developed for high-throughput and sensitive analysis of sub-mL samples. The performance of mu FIA-TLM was validated for detection of hexavalent chromium [Cr(VI)] in water samples. At different sample injection volumes, detection positions, and flow rates, the influence of the reaction time and the diffusion of Cr-diphenylcarbazone (DPCO) complexes on the mu FIA-TLM signal were investigated. Photodegradation of the Cr-DPCO complex was clearly observed when the absorbed photons per Cr-DPCO molecule were above 1600. After optimization of TLM with respect to rapid flows (up to 10 cm s(-1)), we achieved a limit of detection of 0.6 ng mL(-1) for Cr(VI) in a 50 mm deep channel. The impacts of interfering ions [V(V), Mo(VI), and Fe(III)] on Cr(VI) determination were found to be small. Cr(VI) contents in real samples from a cement factory were determined and found to be in good agreement with the results of spectrophotometry. This mu FIA-TLM shows advantages over its conventional counterpart, such as eliminating additional sample conditioning, reducing by over 100 times the sample consumption to sub-mL volumes, and reducing by over 10 times the time required for one sample injection to a few seconds (up to 20 samples per min). The optimized mu FIA-TLM setup can be applied for fast and sensitive analysis of nonfluorescent sub-mL samples in rapidly flowing mediums.