Determination of protein content using a solid phase spectrophotometric procedure

We used a conditioned fiberglass paper to perform the reaction and to retain the reaction products of the Lowry method for protein content. The analytical parameter was obtained by measuring directly the absorbance of the support. Different influencing chemical, support related and instrumental variables were studied and optimized. The usual asymptotic behavior of the analytical function response was improved here by linearizing using a quadratic function. Using 10µl of sample, the applicable concentration range was between 25 and 200mgl-1, with a detection limit of 17mgl-1 and a R.S.D. around 5%. The method was applied to the determination of protein in eggwhite samples coming from different birds. The method proposed here for protein content shows higher sensitivity than solution methods, less dependence on protein nature and higher stability of the species fixed on the support.