Near field thermal lens detector for gradient elution liquid chromatography

Reversed phase liquid chromatography (RP-LC) was applied to the separation of pesticides. The components were detected by a collinear near field thermal lens (NFTL) device. Two sample cells for different directions of liquid flow and interaction lengths were applied. Additionally a transversal near field thermal lensing device was used. A continuous wave argon ion laser was taken as excitation light source at a wavelength of 364 nm. The sensitivity of the NFTL devices were compared with a conventional UV-detector at the same wavelength. The limits of detection (LOD) for the pesticides with the isocratic separation is one order of magnitude better for the collinear NFTL than for the UV-detector. Not only isocratic but also gradient elutions were performed. Small changes of the eluent composition were obtained with linear gradients and large changes with step wise gradients. Using the gradient separation technique, the detection limits of the collinear NFTL are 2–3 times better than for the UV-detector.