A multilayer optical test strip for copper determination in human plasma

A new procedure to determine copper has been proposed using an irreversible and disposable multilayer optical test strip. Two layers form the sensing zone: a copper sensitive and a dialysis layer. The test strip is characterised to be a disposable polyester sheet contained in a circular film 6 mm in diameter and 25 mum in thickness, with all reagents necessary to produce a selective response. The sensing zone was formed by Nafion as polymer, bathocuproine as a chromogenic reagent and p-anisidine as reducer. When it is applied to determination of copper in plasma samples, another layer of hydrogel D-6 is put on this membrane to eliminate the interference of proteins. When the test strip was introduced for 60 min into a plasma sample an orange colour developed. The absorbance at 475 nm was used as the analytical signal. The test strip responded linearly in the range 0.05-1.00 mg L-1. The reproducibility in the measurement of copper at 3.0 mg L-1, was 7.8%. The procedure was applied to the determination of copper in different samples of plasma validating results against a reference method used in clinical laboratory. The method is simple, inexpensive, selective and sensitive.