The Possibility of Signal Enhancement in Liquid Absorption Spectrometry with a Long Capillary Cell Utilizing Successive Total Reflection at the Outer Cell Surface

A new type of long capillary cell (LCC) for liquid absorption spectrometry, in which incident light is transmitted with successive total reflection at the outer cell surface, has been proposed. An uncoated and uncovered capillary tubing of borosilicate glass showed much better light trans-missivity in aqueous solution as a LCC than did one with mirrored walls, and it could be used in coiled form without attenuation of light. An effective pathlength of 85 cm (at A_{1 cm} = 9 × 10⁻⁵) and a baseline stability of 3 × 10⁻⁶ AU were obtained with a 90-cm LCC (i.d. 260 μm, o.d. 400 μm, coiled into 14-cm-diameter coil). The calibration curve was nonlinear because of its nature as a multipath cell. The distribution of light energy inside the LCC was estimated by using a simple statistical model based on the Markov chain.