Development of a micro-fluidic manifold for copper monitoring utilising chemiluminescence detection

Abstract

The progressive development of a micro-fluidic manifold for the chemiluminescent detection of copper in water samples, based on the measurement of light emitted from the Cu(II) catalysed oxidation of 1,10-phenanthroline by hydrogen peroxide, is reported. Micro-fluidic manifolds were designed and manufactured from polymethylmethacrylate (PMMA) using three micro-fabrication techniques, namely hot embossing, laser ablation and direct micro-milling. The final laser ablated design incorporated a reagent mixing channel of dimensions 7.3 cm in length and 250 × 250 µm in width and depth (triangular cross section), and a detection channel of 2.1 cm in length and 250 × 250 µm in width and depth (total approx. volume of between 16 to 22 µL). Optimised reagents conditions were found to be 0.07 mM 1,10-phenanthroline, containing 0.10 mM cetyltrimethylammonium bromide and 0.075 M sodium hydroxide (reagent 1 delivered at 0.025 mL min⁻¹) and 5% hydrogen peroxide (reagent 2 delivered at 0.025 mL min⁻¹). The sample stream was mixed with reagent 1 in the mixing channel and subsequently mixed with reagent 2 at the start of the detection channel. The laser ablated manifold was found to give a linear response (R² = 0.998) over the concentration ranges 0–150 µg L⁻¹ and be reproducible (% RSD = 3.4 for five repeat injections of a 75 µg L⁻¹ std). Detection limits for Cu(II) were found to be 20 µg L⁻¹. Selectivity was investigated using a copper selective mini-chelating column, which showed common cations found in drinking waters did not cause interference with the detection of Cu(II). Finally the optimised system was successfully used for trace Cu(II) determinations in a standard reference freshwater sample (SRM 1640).