Detector cell based on plastic liquid-core waveguides suitable for aqueous solutions: one-to-two decades improved detection limits in conventional-size column liquid chromatography with absorption detection

Abstract

A new type of detector cell is presented, which is designed to improve concentration detection limits in conventional-size reversed-phase column liquid chromatography (LC) with ultraviolet (UV)–visible absorption detection. It is based on a recently developed plastic liquid-core waveguide (LCW), suitable for light guidance through aqueous solutions since the refractive index of the plastic perfluorinated polymeric material (denoted as Teflon AF2400) is 1.29, i.e., smaller than that of water (1.33). An LCW of 90 cm length (280 μm I.D.) was brought into a standard UV–Vis absorption detector and a 1.0 m long quartz optical fibre was installed in the reference channel. This LCW detector cell combines an optical pathlength of about 90 cm with an internal volume of 55 μl. An LC separation of three test analytes – the pesticides atrazine, diuron and linuron, which were detected at 250 nm – provided detection limits of 0.3–0.5 μg/l. This is 30- to 50-fold better than obtained with the standard detector cell. The linear range extended up to about 1 mg/l. As an application 1 ml of tap water spiked with the test analytes at the 0.2 μg/l level was analysed; the results indicated that such a volume is sufficient to reach the 0.1 μg/l threshold value of the European Union directive without using analyte preconcentration.