Microfluidic paper-based analytical devices coupled with coprecipitation enrichment show improved trace analysis of copper ions in water samples.

The present study focused on improving sensitivity to trace levels of Cu(II) by subjecting microfluidic paper-based analytical devices (μ-PADs) to a preconcentration process via coprecipitation using aluminum hydroxide. The experimental conditions were optimized for the pH of the coprecipitation, centrifugation, and amounts of reagents that were deposited onto µ-PADs for the Cu(II) assay. The resultant limit of detection reached as low as 0.003 mg L-1 with a linear range of 0.01-2.00 mg L-1. The relative standard deviations for intra- and inter-day precision were 3.2 and 4.6%, respectively (n = 9). Spiked water samples were analyzed using the μ-PADs after coprecipitation preconcentration. The results were verified by comparing them with those of inductively coupled plasma-optical emission spectrometry (ICP-OES). Recoveries ranged from 97.1 to 104% and from 98.7 to 105% using the present method and ICP-OES, respectively. These results suggest that the simple, highly sensitive, and inexpensive proposed method would be helpful for analyzing trace levels of Cu(II) in water samples in poorly equipped laboratories.