Abstract: A method for detecting and measuring a metal ion in an aqueous medium includes derivatizing a solid phase extraction material with a reactive material that undergoes a chemical reaction when contacted with the metal ion. The solid phase extraction material and the reactive material are positioned in an aqueous medium containing the metal ion, such that the metal ion contacts the reactive material and causes it to chemically react. The reaction of the reactive material is detected by optical spectroscopy to detect and measure the metal ion.