Gold leaf electrochemical flow cell for determination of iodide in nuclear emergency tablets.

This work introduces an innovative gold-leaf flow cell for electrochemical detection in flow injection (FI) analysis. The flow cell incorporates a hammered custom gold leaf electrochemical sensor. Hammered gold leaves consist of pure gold and are readily available in Thailand at affordable prices (approximately $0.085 for a sheet measuring 40 mm × 40 mm). Four sensing devices can be made from a single sheet of this gold leaf, resulting in a production cost of approximately $0.19 per sensor. Each electrochemical sensor has the gold leaf as the working electrode, together with a printed carbon strip, and a printed silver/silver chloride strip as the counter and reference electrodes, respectively. Initial investigations using cyclic voltammetry of a standard 1000 µmol L⁻1 iodide solution in 60 mmol L⁻1 phosphate buffer (PB) solution at pH 5, demonstrated performance comparable to that of a commercial screen-printed gold electrode. The hammered gold leaf electrode was then installed in a commercial flow cell as part of an FI system. A sample or standard iodide solution (100 µL) is injected into the first carrier stream of phosphate buffer (PB) solution, which then merges to mix with the second stream of the same buffer solution before flowing into the flow cell for amperometric detection of iodide. The optimized operating conditions include a fixed potential of +0.39 V (vs Ag/AgCl), and a total flow rate of 3 mL min⁻1. A linear calibration is obtained in the concentration range of 1 to 1000 µmol L⁻1 I- with a typical equation of µA = (0.00299 ± 0.00004) × (µmol L-1 I-) + (0.021 ± 0.020), and R2 = 0.9994. Analysis of iodide using this gold leaf-FI system is rapid with sample throughput of 86 samples h⁻1 and %RSD of a sample of 100 µmol L⁻1 I⁻ of 1.2 (n = 29). The limit of detection, (calculated as 2.78 × SD of regression line/slope), is 27 µmol L⁻1 I-. This method was successfully applied to determine iodide in nuclear emergency tablets.

Green synthesis of silver nanoparticles using Coffea canephora fruit skin extract and its application for mercury detection in face cream samples.

Mercury is one of the most toxic heavy metals causing harmful effects on the human body; meanwhile, mercury is found in some face cream products to give a whitening effect. The upper limit concentration of mercury in skin-lightening products defined by the Food and Drug Administration (FDA) is under one mg/L as Hg2+. A new green analytical spectrophotometric method for mercury analysis has been developed by employing a biological reagent from fruit skin extract of robusta coffee (Coffea canephora) as a bioreductor for silver ions as well as a stabilizer for the AgNPs product. The detection principle of this method is based on the decrease of the color intensity of silver nanoparticles (AgNPs) after the addition of Hg2+ ions due to the re-oxidization of the AgNPs by Hg2+ ions to colorless Ag+ ions. To achieve the most significant sensitivity, linearity of measurement, and validity, the method was optimized toward the volume of AgNPs and reaction time. In this research, the synthesized AgNPs were also characterized by UV-Vis Spectrometry as well as a particle size analyzer (PSA) to determine the size of nanoparticles. The result showed that the optimum conditions were attained at 4 mL AgNPs solution and 3-min reaction resulting in a linear measurement of Hg2+ in the range of 0-15 mg/L with LOD and LOQ of 0.039 and 0.130 mg/L, respectively. This method is quite selective and has been validated by applying it to real face cream samples with satisfactory results supported by average recoveries of close to 100%.

An application study of membraneless-gas separation microfluidic paper-based analytical device for monitoring total ammonia in fish pond water using natural reagent.

The membraneless-gas separation microfluidic paper-based analytical device (ML-GS µPAD), consisting of donor, spacer, and acceptor layers, was developed to monitor total ammonia in fish pond water. The principle of the analysis involved the addition of sodium hydroxide solution to the sample zone in the donor layer containing ammonia/ammonium, and the produced ammonia gas diffuses through the spacer to the detection zone in the acceptor layer containing red rose extract to produce a color change from pink to blue corresponding to the ammonia/ammonium concentration. Under optimum conditions, the proposed method provided good linearity of ammonia in the range concentration of 0-100 mg L-1 (R2 = 0.9993) with LOD and LOQ of 2.25 and 7.51 mg L-1, respectively. This method was successfully applied to fish pond water samples without significant influence of interfering compounds with recoveries in the range of 103-110%, indicating good selectivity and accuracy of the proposed method.

Simple and Equipment-Free Paper-Based Device for Determination of Mercury in Contaminated Soil.

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.