Lens-coupled liquid core waveguide for ultraviolet-visible absorption spectroscopy

We have developed and characterized a modular liquid core waveguide (LCW) assembly for use in a commercial spectrophotometer to measure very low light absorbance values for dilute aqueous solutions in both the ultraviolet and visible wavelengths. The sample cell in this assembly is composed of a ∼1m, pure Teflon® AF 2400 tube that is coupled to the spectrophotometer light path with a quartz lens and windows. Spectrophotometric absorbance measurements of test solutions (e.g., dilute sodium nitrate and hydrogen peroxide) produce clear and distinct spectra that exhibit a lower limit of detection of 3mAU between 240 and 640nm. At absorbances above 10mAU our LCW system produces spectra from multiple independent injections that have a relative standard deviation of less than 10% and average absorbances within 5% of calculated values based on published molar absorptivities.