Colorimetric Determination of Lead Using Gold Nanoparticles

A combined homogeneous assay and colorimetric determination method using gold nanoparticles was developed for rapid determination of lead(II) in contaminated natural waters. The presence of lead(II) in the colloidal gold suspension causes a change in the absorbance of the suspension. An increase in the absorption property at 595nm is accompanied by a change in the size of the gold nanoparticles. High concentrations of lead cause aggregation of the gold colloids. Colloidal gold nanoparticles were synthesized using tannic acid as the reducing agent; this reagent allowed selective determination of lead in 10 mu L of water, with a detection limit of 310ngmL(-1) with an analysis time of 5min. The coefficient of variation for lead(II) within the working range of the assay (520ngmL(-1)-13 mu gmL(-1)) varied from 1.3% to 9.2%. The limit of detection using this method with a sample volume of 50 mu L was 60ngmL(-1). The coefficient of variation for lead over the working range of the determined concentrations (80ngmL(-1)-25 mu gmL(-1)) varied from 0.2% to 9.3%, while the values for the inter-day assay (n=8) were less than 10%. The method was employed for the analysis of river, lake, marsh, and spring water; the recovery of lead was determined to be 72.5%-130% for 10 mu L of water and 93.6%-114.7% for 50 mu L.