Application of Newton’s Zero Order Caustic for Analysis and Measurement: Part-I Absorbance

When light is incident upon a liquid solution droplet containing a light absorbing solute and it is formed into a spheroid shape, absorbance can be measured and related to concentration of the light absorbing species in a manner analogous to standard spectrophotometry. However, the spheroid sample acts as a focusing lens through the method of Newton’s zero order caustic resulting in a higher intensity of light within the sample and light that reaches the detector. As a result, linearity of the Beer-Lambert law can be observed without stray light correction at values of absorbance greater than 1. Also, fluorescence can be observed using lower excitation energy than what would normally be required. In order to illustrate measurement and detection, using Newton’s zero order caustic, solutions of two food dyes (Brilliant Blue FCF and tartrazine) were studied using matching red (660 nm) and blue (430 nm) photodiodes.