For determination of copper, the bicinchoninate reagent is added to a neutral buffered sample containing copper. The reaction between copper and the reagent causes a purple colored complex to form; the greater the concentration, the deeper the color. A color comparator cube is included for an accurate, side-by-side, visual analysis to determine copper concentration. These reagents are designed to be used with samples that have an expected range of 0.0 to 2.5 mg/L (ppm) copper.