An Improved Reflection Colorimeter Integrated with a Coaxial Optical-fiber Cable for Highly Sensitive Solid-phase Colorimetry Using a Membrane Filter

Highly sensitive solid-phase colorimetry for nickel ion was demonstrated using an improved reflection colorimeter equipped with a coaxial optical-fiber cable. The nickel complex with α-furil dioxime was collected on a small-size membrane filter embedded in a disposable syringe filter unit. The leading edge of the optical-fiber cable was connected to the syringe filter unit via a Luer-lock fitting, and the color intensity of the sample on the filter was evaluated accurately. The detection limit was 0.8 ng in 2.5 mL of the complex solution (0.3 μg L−1). This improved configuration is applicable to highly sensitive on-site analysis without expensive instruments nor high laboratory skills.