Mid-IR Quantum Cascade Lasers as an Enabling Technology for Analytical Chemistry

After providing an overview on the state-of-the-art of measuring condensed phase samples by quantum cascade lasers (QCL), this presentation will focus on protein analysis. The qualitative analysis of mid-IR spectra of aqueous protein solutions provides information on the secondary structure elements present in the proteins under study. In this work an external cavity (EC)-QCL was used for performing transmission measurements of different aqueous protein solutions in a CaF2 flow cell with optical paths up to 75 mu m. The strong temperature dependence of the nu(2)-band of water overlapping the amide I absorption band (similar to 1650 cm(-1)) required a temperature stability of +/-0.005 degrees C. Successful determination of the secondary structures of albumin and beta-lacto-globulin was achieved in the low g/L concentration range.