Determination of Proteins in a Mesofluidic Lab-on-Valve System

The application of a mesofluidic lab-on-valve system to the spectrophotometric determination of protein was investigated. Protein species in the sample solution reacts rapidly with Congo red at pH 4.1, which forms a complex with a maximum absorption at 496 nm. A univariant approach was used for the optimization of the experimental parameters. A sample volume of 20 μl was used along with 4.0 μl of Congo red solution of 0.9 g l⁻¹, and a flow rate for the detection process of 20 μl s⁻¹ was used. Under optimal conditions, a linear calibration curve was obtained in the range of 12.5–200 μg ml⁻¹ of bovine serum album, along with a detection limit (3σ) of 5.6 μg ml⁻¹ and a sampling frequency of 60 per hour. Protein concentrations in human serums, urine, milk, and yoghourt were determined using this procedure, and satisfactory agreements were obtained with that achieved using the Coomassie brilliant blue method.