Silver-doped hydroxyapatite for formaldehyde determination by digital-image colorimetry

Silver-hydroxyapatite material (Ag-HAP) was first proposed as material for trace-level formaldehyde detection based on Tollens' reaction on the material surface. By using this Ag-HAP material, the chemical reduction caused by formaldehyde occurred directly on the solid surface. The material color changed from off-white to the yellow or brown of silver nanoparticles depending on the formaldehyde concentration. The color intensity of the materials was measured from their smartphone digital images using Image-J software. The effect of silver ion concentration, sodium hydroxide concentration, contact time, and sample volume on formaldehyde detection were investigated. Under optimized conditions, the working range for formaldehyde detection was determined to be 15 to 200 μg L^-1. The method was successfully applied to detect trace formaldehyde in water samples and a recovery of 86 to 111%, with an RSD of 3 to 8%, was observed. With a lowest concentration for the detection of 15 μg L^-1 and good accuracy and precision, the method showed promise for formaldehyde determination.