Image-based luminescence detection for quantitative determinations in continuous flow analysis microsystems

Abstract

The use of an ordinary webcam to detect luminescence in continuous flow analysis microsystems is described, as well as evaluation of the proposed strategy for determining acetaminophen in tablets and to assess the hardness of mineral waters. Lab-made microfluidic devices were arranged in a box to avoid external light influence and the camera was fixed to the top of the box, aligned to flow cells, in which RGB detection was performed at pre-selected pixels of real time images. For determining acetaminophen in tablets, the merging zones principle was used to mix the samples or drug standard solutions (0.10–0.50 mg mL⁻¹) with OCl⁻¹ solution (0.05% (m/v)) prior to the confluence with luminol (2.0 mmol L⁻¹) and chemiluminescence readings. The analytical curve based on the quenching of the blue color response showed a linear relationship (R² = 0.996) and the LOD was estimated to be 0.03 mg mL⁻¹. In addition, no significant differences were found on comparison of the contents of drugs determined by the proposed method with those on medicine labels. Fluorometric determination of mineral waters' hardness was performed using a blue LED and optical fibers as an excitation source. Sample or standard solutions (0.12–0.62 mmol L⁻¹ in Ca²⁺) were merged with 0.4 g L⁻¹ calcein solution and propelled to the detection zone. The response to green color showed a linear relationship (R² = 0.994) with the studied concentrations, and an LOD of 0.08 mmol L⁻¹ was estimated for the method. Also, the water hardness determined by the proposed method offered no significant difference at the 95% confidence level when compared with results obtained with complexometric titrations.