Analysis of the optical properties of bile

Invasive bile determination is very useful in the diagnosis of many gastric pathologies. Al the moment, this measurement is performed with Bilitec 200 0, an optical fiber sensor, that is based on absorption by bilirubin. Never theless, erroneous evaluations are possible, due to the different configura tions which the bilirubin molecule can adopt. The optical behavior of human samples of pure bile and bile+gastric juice has been examined using an opt ical fiber spectrophotometer and two suitably modified Bilitec 2000 units. A protocol has been established for the treatment of biological fluids, in order to make it possible to study the behavior of their optical properties as a function of pH and concentration without causing any alteration in th e samples. The analysis of pH dependence evidenced the presence of differen t calibration curves at different pH values: the self-aggregation of the bi lirubin molecules observed in pure bile samples was almost totally absent i n the gastric samples. Measurements carried out on Bilitec 2000 showed that the most appropriate wavelength for bilirubin detection in the stomach sho uld be 470 nm. (C) 2000 Society of Photo-Optical instrumentation Engineers. [S1083-3668(00)00403-2].