A composable module-type cyanide microfluidic sensor based on polydimethylsiloxane membrane pervaporative sampling with sodium bicarbonate internal-pressure regulation and dual fluorescence/potentiometric monitoring

This paper demonstrates a reliable and safe microfluidic sensor on the monitoring of weak-acid dis-sociable cyanide (WAD-CN-) from environmental waters. The sensor chip consists of three parts: a pervaporative membrane sampling module, a fluorescence labelling/detection module and a cyanide ion selective-electrode (CN--ISE) potential detection module. Cyanide pervaporation was achieved by in situ sample acidification to produce hydrogen cyanide (HCN) through a gas-diffusing polydimethyl-siloxane (PDMS, 4-5 mu m thickness) membrane. HCN was recovered using a lye solution and subsequently split into two streams for the dual fluorescence/potentiometric monitoring. Dual fluorescence and CN--ISE potential monitoring were performed by applying two indispensable treatment to the split streams with naphthalene-2,3-dicarboxaldehyde (NDA)-glycine (Gly) and total-ionic-strength-adjustment buffer solution (TISAB), respectively. The parameters in the pervaporation process and both detections were optimized. To increase the sensitivity at low concentrations, a sodium bicarbonate solution was introduced into the sample stream as a chemical pressure regulator, which maintained a constant pressure in the channel by continuously producing CO2. To prevent the loss of produced gas, the channels, except for the membrane, were coated by a polyvinylsilazane (PVSZ) polymer solution and cured. Under an HCl donor stream (0.5 mol L-1; 15 mu L min(-1)) and a sodium hydroxide acceptor stream (0.1 mol L-1; 20 mu m/min), 65.7% of transmission rate (RSD = 0.86%; n = 3 for 0.1 mg L-1 CN-) was achieved. The pervaporative sampling method effectively minimized the interferences (except organic thiols) from the environmental matrices during the detection of cyanide in both detection modules. The validity and quality of the assay were assessed in terms of the linearity 5-500 mu g L-1 (R-2 = 0.9992) and limit of detection (c(L)) 0.015 mu g L-1 with the fluorescence method and those are 2.6-1000 mu g L-1 (R-2 = 0.998), and 1.1 mu g L-1 with the CN--ISE potentiometric detection. The cyanide levels in waste waters were determined using the standard addition method and verified using the EPA method OIA-1677. Furthermore, a microchip electrophoresis (MCE) analysis was performed to investigate the systemic errors from the mercapto-interferences of the samples. The developed microfluidic sensor was applied to monitor WAD-CN in waste waters. The sensor is a flexible, extensible, and environmentally friendly alternative for WAD-CN- monitoring. (c) 2017 Elsevier B.V. All rights reserved.