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This work presents new chemical sensing devices called "membraneless gas-separation microfluidic paper-based analytical devices" (MBL-GS μPADs). MBL-GS μPADs were designed to make fabrication of the devices simple and user-friendly. MBL-GS μPADs offer direct quantitative analysis of volatile and nonvolatile compounds. Porous hydrophobic membrane is not needed for gas-separation, which makes fabrication of the device simple, rapid and low-cost. A MBL-GS μPAD consists of three layers: "donor layer", "spacer layer", and "acceptor layer". The donor and acceptor layers are made of filter paper with a printed pattern. The donor and acceptor layers are mounted together with a spacer layer in between. This spacer is a two-sided mounting tape, 0.8 mm thick, with a small disc cut out for the gas from the donor zone to diffuse to the acceptor zone. Photographic image of the color that is formed by the reagent in the acceptor layer is analyzed using the ImageJ program for quantitation. Proof of concept of the MBL-GS μPADs was demonstrated by analyzing standard solutions of ethanol, sulfide, and ammonium. Optimization of the MBL-GS μPADs was carried out for direct determination of ammonium in wastewaters and fertilizers to demonstrate the applicability of the system to real samples.

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This work presents a simple and innovative protocol employing a microfluidic paper-based analytical device (µPAD) for equipment-free determination of mercury. In this method, mercury (II) forms an ionic-association complex of tetraiodomercurate (II) ion (HgI42−(aq)) using a known excess amount of iodide. The residual iodide flows by capillary action into a second region of the paper where it is converted to iodine by pre-deposited iodate to liberate I2(g) under acidic condition. Iodine vapor diffuses across the spacer region of the µPAD to form a purple colored of tri-iodide starch complex in a detection zone located in a separate layer of the µPAD. The digital image of the complex is analyzed using ImageJ software. The method has a linear calibration range of 50–350 mg L−1 Hg with the detection limit of 20 mg L−1. The method was successfully applied to the determination of mercury in contaminated soil and water samples which the results agreed well with the ICP-MS method. Three soil samples were highly contaminated with mercury above the acceptable WHO limits (0.05 mg kg−1). To the best of our knowledge, this is the first colorimetric µPAD method that is applicable for soil samples including mercury contaminated soils from gold mining areas.

This work describes development of a new spectrophotometric flow analysis technique suitable for monitoring of ethanol content in gasohol fuel. In this technique, the concept of membraneless gas-diffusion (MBL-GD) was applied with one-step aqueous extraction of gasohol (1:2 gasohol:water). Segments of aqueous extract and color developing reagent were allowed to flow into two separate channels in the MBL-GD device. Inside the device, ethanol vapor can diffuse across a small headspace between the two channels (donor and acceptor). Introduction of an air-segment behind the zone of acceptor reagent to stop dispersion of the colored zone has greatly improved the rapidity of analysis using this MBL-GD technique. Two methods were developed for quality control of gasohol by measuring ethanol content. Method I is suitable for direct calibration of E5 and E10. Method II is recommended for E20. These methods have high accuracy with good precision (% RSD: 1 to 4.9, n=45) and have a sample throughput of 26 samples h -1 . E10 samples were compared with analysis using a standard GC method.

This work presents the first flow system for direct analysis of iodide and creatinine suitable for screening of human urine samples. The system had a mini-column packed with strong anion exchange resin for on-line extraction of iodide. After injection of a sample on the column the unretained urine sample was analyzed for creatinine in one section of the flow system using the Jaffe's reaction with spectrometric detection at 520 nm. Iodide was eluted off with 1.42 mL 5 M NaNO 3 . A 150 mL fraction of the eluate was analyzed in another section of the same flow system for iodide using the kinetic-spectrometric Sandell-Kolthoff reaction. At the optimum condition, the sample throughput was 12 samples per h. The linear working range covered the normal levels of iodide and creatinine in human urine: 0-200 mg I L À1 and 50-1200 mg creatinine L À1 , respectively. Recoveries tested in 10 samples were 87-104% for iodide and 89-104% for creatinine.Bland-Altman plots (n ¼ 50) showed that the scatter of the differences between values obtained by this method and those of reference methods, for both iodide and creatinine, was within mean AE 2SD.