Optical photothermal detection in HPLC

A mode-mismatched parallel dual-beam thermal lens spectrometer with a far-field single-channel detector system was used as a detector in HPLC. An expert estimation of the measurement results was applied to optimize the optical-scheme configuration of the spectrometer to achieve the longest linear calibration range and highest repeatability under chromatographic flow conditions. Chelates with 4-(2-pyridylazo)resorcinol were separated and determined with the limits of detection of n × 10−8–n × 10−7 mol L−1; the relative standard deviation of measurements was 46%. Xylenol Orange, 4-(2-thiazolylazo)resorcinol, and dithizone were studied as post-column reagents in thermal lens detection in ion chromatography. The limits of detection were n × 10−8–n × 10−7 mol L−1; the linear calibration ranges were about three orders; the relative standard deviation of measurements was 3–7%. A combined photothermal–refractometric detector for HPLC based on a polarization interferometer is proposed. Metal complexes as 4-(pyridylazo)resorcinol chelates (limits of detection of n × 10−8–n × 10−7 mol L−1) and sugars (limits of detection of 10–20 ng L−1) were investigated as model substances. Obtained results were compared with results for traditional detectors, which show that photothermal detection has higher sensitivity than photometric and other absorption detectors.