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.

Disposable Microchamber with a Microfluidic Paper-Based Lid for Generation and Membrane Separation of SO2 Gas Employing an In Situ Electrochemical Gas Sensor for Quantifying Sulfite in Wine.

This work presents a fully disposable microchamber for gas generation of a sample solution. The microchamber consists of a cylindrical well-reactor and a paper-based microfluidic lid (µFluidic lid), which also serves as the reagent loading and dispensing unit. The base of the reactor consists of a hydrophobic membrane covering an in-house graphene electrochemical gas sensor. Fabrication of the gas sensor and the three-layer µFluidic lid is described. The µFluidic lid is designed to provide a steady addition of the acid reagent into the sample solution instead of liquid drops from a disposable syringe. There are three steps in the procedure: (i) acidification of the sample in the reactor to generate SO2 gas by the slow dispensing of the acid reagent from the µFluidic lid, (ii) diffusion of the liberated SO2 gas through the hydrophobic membrane at the base of the reactor, and (iii) in situ detection of SO2 by cathodic reduction at the graphene electrode. The device was demonstrated for quantitation of the sulfite preservative in wine without heating or stirring. The selectivity of the analysis is ensured by the combination of the gas-diffusion membrane and the selectivity of the electrochemical sensor. The linear working range is 2-60 mg L-1 SO2, with a limit of detection (3SD of intercept/slope) of 1.5 mg L-1 SO2. This in situ method has the shortest analysis time (8 min per sample) among all voltammetric methods that detect SO2(g) via membrane gas diffusion.

Simplified fabrication of laminated paper-based analytical device (LPAD) with color-palette mobile app for analysis of salicylic acid in pharmaceutical products.

In this work, we present for the first time, a simplified fabrication of a laminated paper-based analytical device (LPAD) with a free-mobile app, Palette Cam, for image analysis. A filter paper is cut in a rectangular shape (9 × 3 cm) and placed between a top laminating sheet with punched holes and a bottom laminating sheet. The holes allow accessibility of liquid on the paper. Thermal lamination is then employed to complete the fabrication of LPAD. Our simplified design reduces a tedious alignment of small pieces of paper to the holes. We demonstrated the LPAD with an analysis of salicylic acid in pharmaceutical products. Each 4 µL of ferric reagent and sample was dispensed on the LPAD. Smartphone was used to capture images. The RGB (red green blue) color intensity from the Palette Cam was converted into a logarithm color ratio. Our LPAD is simplified, cost-effective and able to be a portable device.

Simple gunshot residue analyses for estimating firing distance: Investigation with four types of fabrics.

This work presents two simple methods for estimating the firing distance from the gunshot residues (GSRs) on fabric targets. Four types of fabric targets, namely twill weave denim cotton-polyester (80/20), jersey knitting 100% cotton, plain weave cotton-polyester (80/20) and plain weave cotton-polyester (60/40), were employed. The firing tests were carried out using these white fabrics as targets at distances of 5-100 cm, respectively. In the first method, digital images of the black GSRs on fabric materials were recorded inside an illuminated box and the inverted gray intensity values were plotted against the firing distances. Since the plots of all fabrics are not significantly different, the estimation of firing distance employs the same exponential curve for all test fabrics. Although simple, the imaging method is not suitable for dark-colored materials. A chemical-based method was therefore developed as an alternative method. In the second method, a small disposable microfluidic paper-based analytical device (µPAD) was employed for detecting Pb(II) extracted from the GSRs. The µPAD method uses the measurement of the length of a narrow band of a pink color resulting from reaction between rhodizonate reagent and the Pb(II) extract. The plots indicated that the data of thick denim material are significantly different to other test fabrics which are much thinner. These three fabrics share the same estimation curve. However, it is recommended that the separate estimation curve for denim materials must be used. Both methods are suitable for short range firing distance, no further than 60 cm, since at greater distances the inverted gray intensity and the 'band-length' methods are unable to detect the GSRs.

WinMLR program for the determination of sorbic and benzoic acids in food samples.

The program WinMLR has been developed to quantify sorbic and benzoic acids in soft drinks, fruit juices, and soy sauce by making a multilinear regression treatment of experimental data to a linear combination of standard signals. The spectra of sorbic and benzoic acid and samples were obtained from a conventional spectrophotometer, which has been saved in an ASCII file to be applied with the WinMLR program. Before to determine sorbic and benzoic acids in samples, the wavelength validation and calibration parameters were studied. Standard solutions of sorbic and benzoic acids were used for the calibration parameters to measure the individual analyte. If the sample has simultaneously both compounds, it is better to choose the synthetic mixture for the calibration parameters. This technique provides a good recovery in the range of 80.4-104.8% without a complicated and expensive instrument.

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.

Development of a microfluidic membraneless vaporization flow system for trace analysis of arsenic.

A new design of a membraneless vaporization (MBL-VP) unit coupled with a specific flow system is presented for the determination of arsenic at trace levels using a hydride generation process. The MBL-VP unit contains two concentric conical reservoirs, with the outer cone selected as the donor reservoir. The volume of the outer donor reservoir is thereby greater than the acceptor volume, necessary for holding sufficient sample and reagents for the generation of arsine gas by reaction between As(iii) and sodium borohydride under acidic conditions. The arsine gas diffuses into the narrow headspace and is absorbed by an aliquot of 150 µL of mercuric chloride acceptor solution. The resulting reaction produces hydronium ions which is monitored by the absorbance change at 530 nm of the methyl orange indicator added in the acceptor solution. To decrease the detection limit, the aspiration and removal of the donor plug, comprising the sample, borohydride and acid, into and out of the donor cone are repeated several times, while the acceptor solution is kept unchanged. As a result, analysis of arsenic was achieved in the range of 10 to 100 µg L-1 with a detection limit of 8 µg L-1. Application to surface water was investigated. Percent recoveries of spiked surface water samples were in the range of 94-110%. For comparison of total arsenic (As(iii) and As(v)), the results obtained from the developed method are not statistically different from the ICP-OES method.

Dual-Purpose Photometric-Conductivity Detector for Simultaneous and Sequential Measurements in Flow Analysis.

This work presents a new dual-purpose detector for photometric and conductivity measurements in flow-based analysis. The photometric detector is a paired emitter-detector diode (PEDD) device, whilst the conductivity detection employs a capacitively coupled contactless conductivity detector (C4D). The flow-through detection cell is a rectangular acrylic block (ca. 2 × 2 × 1.5 cm) with cylindrical channels in Z-configuration. For the PEDD detector, the LED light source and detector are installed inside the acrylic block. The two electrodes of the C4D are silver conducting ink painted on the PEEK inlet and outlet tubing of the Z-flow cell. The dual-purpose detector is coupled with a sequential injection analysis (SIA) system for simultaneous detection of the absorbance of the orange dye and conductivity of the dissolved oral rehydration salt powder. The detector was also used for sequential measurements of creatinine and the conductivity of human urine samples. The creatinine analysis is based on colorimetric detection of the Jaffé reaction using the PEDD detector, and the conductivity of the urine, as measured by the C4D detector, is expressed in millisiemens (mS cm-1).

Simple Flow-Based System with an In-Line Membrane Gas-liquid Separation Unit and a Contactless Conductivity Detector for the Direct Determination of Sulfite in Clear and Turbid Food Samples.

This study presents a simple flow-based system for the determination of the preservative agent sulfite in food and beverages. The standard method of conversion of sulfite ions into SO2 gas by acidification is employed to separate the sulfite from sample matrices. The sample is aspirated into a donor stream of sulfuric acid. A membrane gas-liquid separation unit, also called a 'gas-diffusion (GD)' unit, incorporating a polytetrafluoroethylene (PTFE) hydrophobic membrane allows the generated gas to diffuse into a stream of deionized water in the acceptor line. The dissolution of the SO2 gas leads to a change in the conductivity of water which is monitored by an in-line capacitively coupled contactless conductivity detector (C4D). The conductivity change is proportional to the concentration of sulfite in the sample. In this work, both clear (wine) and turbid (fruit juice and extracts of dried fruit) were selected to demonstrate the versatility of the developed method. The method can tolerate turbidity up to 60 Nephelometric Turbidity Units (NTUs). The linear range is 5-25 mg L-1 SO32- with precision < 2% RSD. The flow system employs a peristaltic pump for propelling all liquid lines. Quantitative results of sulfite were statistically comparable to those obtained from iodimetric titration for the wine samples.

Green analytical method for simultaneous determination of salinity, carbonate and ammoniacal nitrogen in waters using flow injection coupled dual-channel C4D.

A flow injection analysis system (FIA) for the simultaneous determination of salinity, carbonate and ammoniacal nitrogen has been developed and reported in this paper. FIA incorporating membrane units was used, not only for the separation of the gaseous carbon dioxide and ammonia, but also for on-line dilution in the salinity measurement. The sample was injected via a 10-port valve with two sample loops. One loop was used for salinity and carbonate measurements and the second loop for ammoniacal nitrogen determination. A dual-channel capacitively coupled contactless conductivity detector was assembled in a single shielding box. Input voltage from the same AC power supply was fed to the input electrodes of both C4D cells. One channel of the C4D was used to monitor the change in conductivity of an acceptor stream that carried a zone of the water sample that has passed through the on-line dilution unit. Conductivity of this zone relates directly to the salinity of the sample. The same sample zone was next acidified to generate carbon dioxide gas that diffused through a hydrophobic membrane of the first gas diffusion (GD) unit. The zone of dissolved carbon dioxide in acceptor stream of water flowed into the same C4D cell as for the salinity measurement, but arriving at a later time. Concurrently, the second channel of the C4D monitored the change in conductivity of the acceptor stream in the second GD unit due to the diffusion of ammonia gas generated by the reaction of base with the sample injected from the second sample loop. The change in conductivity at this second C4D cell correlates with the concentration of ammoniacal nitrogen present in the sample. The proposed method is low cost, simple, rapid and sensitive. The limit of quantitation for salinity, carbonate and ammoniacal nitrogen are 0.31mmolL-1, 1.85 µmol L-1, respectively. Throughput of 20 samples h-1 for simultaneous analysis can be achieved with RSD of less than 3.8%. The system had been applied to the determination of salinity, carbonate and ammoniacal nitrogen in 15 water samples, with results in agreement with those obtained using comparison methods.

Microfluidic Paper-based Analytical Device for Quantification of Lead Using Reaction Band-length for Identification of Bullet Hole and Its Potential for Estimating Firing Distance.

A low-cost and user-friendly microfluidic paper-based analytical device (µPAD) was developed for identification of bullet hole from gunshot residue (GSR) on cotton fabric target. The device (25 × 82 mm) is made of filter paper with a printed pattern consisting of a circular sample loading reservoir (6 mm i.d.), a circular waste reservoir (4 mm i.d.) and a straight flow channel (3 mm wide and 60 mm long). A sticker with a ruler scale in millimeters was mounted alongside the channel. The straight channel is first impregnated with rhodizonate and dried at ambient temperature. Tartrate extract of the target fabric is loaded on the sample reservoir. If Pb(II) ions are present in the extract, pink streak of Pb(II)-rhodizonate precipitate is formed as the sample solution flows from the reservoir along the channel. The length of the pink strip is employed to estimate the firing distance.

Simple in-house flow-injection capillary electrophoresis with capacitively coupled contactless conductivity method for the determination of colistin.

An in-house flow-injection capillary electrophoresis with capacitively coupled contactless conductivity detection method was developed for the direct measurement of colistin in pharmaceutical samples. The flow injection and capillary electrophoresis systems are connected by an acrylic interface. Capillary electrophoresis separation is achieved within 2 min using a background electrolyte solution of 5 mM 2-morpholinoethanesulfonic acid and 5 mM histidine (pH 6). The flow-injection section allows for convenient filling of the capillary and sample introduction without the use of a pressure/vacuum manifold. Capacitively coupled contactless conductivity detection is employed since colistin has no chromophore but is cationic at pH 6. Calibration curve is linear from 20 to 150 mg/L, with a correlation coefficient (r(2) ) of 0.997. The limit of quantitation is 20 mg/L. The developed method provides precision, simplicity, and short analysis time.

Cross injection analysis: concept and operation for simultaneous injection of sample and reagents in flow analysis.

This work presents a new flow injection strategy, called 'cross injection analysis' or CIA, an alternative cost-effective approach in flow analysis. The flow platform is made from a rectangular acrylic block, approximately 5×3×1.5 cm (x×y×z), with crossing cylindrical channels drilled out along the x- and y-axis of the block. The outlet from the single x-axis channel is connected to a detector flow cell. This channel is filled with the carrier solution. The flow in the x-axis channel is driven by a computer controlled single-channel peristaltic pump. The multiple y-axis channels, running perpendicular to the x-channel, are connected to a multi-channel peristaltic pump. These channels contain the sample and reagent solutions that flow across the intersection zones of the channels. To mix the sample and reagent with subsequent detection of the reaction zone, flow is applied along the x-axis channel, while flow in the y-axis channels is stopped. We successfully demonstrated the validity of the CIA technique by the spectrometric determination of Fe(II) using 1,10-phenanthroline and the speciation of Fe(II) and Fe(III). To place the CIA technique within the context of flow analysis, a brief overview of the evolution of flow injection analysis and its later innovative development is included.

Direct injection of human serum and pharmaceutical formulations for glucosamine determination by CE-C(4)D method.

A simple CE-C(4)D method has been developed for the determination of glucosamine by direct injection of human serum and pharmaceutical samples. Glucosamine was electrokinetically injected and analysed in its protonated form using 20mM MES/His (pH 6) as background electrolyte in order to separate it from the matrix and to provide a better response to the C(4)D detector. Separation of glucosamine in human serum and pharmaceutical samples was performed in 3 min without the need for protein precipitation or matrix removal. Good precision in terms of %RSD for the migration time and peak area were less than 1.91% (n = 10). The conductivity signal was linear with glucosamine concentration in the range 0.10-2.50mg/mL, with a detection limit of 0.03 mg/mL. Recoveries of glucosamine in serum and pharmaceutical samples were 86.5-104.78%. The method was successfully applied for the determination of the glucosamine content in pharmaceutical formulations and validated with high performance liquid chromatography (HPLC). Good agreements were observed between the developed method, label values and the HPLC method. Glucosamine could be detected in spiked serum sample by direct injection. This was not possible by HPLC due to co-eluting interferences.

A low-cost method for determination of calcium carbonate in cement by membraneless vaporization with capacitively coupled contactless conductivity detection.

This work presents a flow analysis method for direct quantitation of calcium carbonate in cement without pretreatment of the sample. The method is based on online vaporization of CO(2) gas following acidification of the sample inside a small chamber that has a flow of acceptor solution passing around it. Solubilization of the CO(2) gas into the acceptor stream changes the conductivity of the acceptor solution causing an increase of signal at the capacitively coupled contactless conductivity detection (C(4)D) placed at the outlet of the vaporization chamber. This chamber is an adaption from previous work reported on 'membraneless vaporization' (MBL-VP). The method can be used in the quality control of production of mixed cement. These cement materials usually have calcium carbonate contents at high concentration range (e.g., 33-99% (w/w) CaCO(3)). Analysis of samples by this method is direct and convenient as it requires no sample pretreatment. The method is low-cost with satisfactory accuracy and acceptable precision.

Novel oxidation reaction of prochlorperazine with bromate in the presence of synergistic activators and its application to trace determination by flow injection/spectrophotometric method.

A simple and fast flow injection spectrophotometric method for the determination of bromate in water samples was developed. The detection system is based on the oxidation of prochlorperazine (PCP) with bromate in strongly acidic medium. Large amounts of chloride and bromide was found, for the first time, to act as an activator, and to enhance the sensitivity for bromate detection. The oxidation product of PCP gives pink color, which can be used to monitor the reaction spectrophotometrically at 525 nm. Under the optimal conditions, the method is selective; only nitrite, chlorite and hypochlorite can interfere with the determination of bromate. The elimination of these three ions is discussed. The calibration graph for bromate determination was linear in the range of 10-130 microg L(-1) with a detection limit of 2.3 microg L(-1). The repeatability was satisfactory, with the relative standard deviation of 1.1% (25 microg L(-1), n=10). The sample throughput was 44 h(-1). The proposed method was found to be highly reliable for screening drinking waters containing bromate, which is above or below legislation limit of 10 microg L(-1).

Kinetic-spectrophotometric method for the determination of trace amounts of bromide in seawater.

A novel simple, sensitive and rapid kinetic-spectrophotometric method is proposed for the determination of trace amounts of bromide. The method is based on its catalytic effect on the oxidation of methylene blue (MB) by hydrogen peroxide in strongly acidic solution. The oxidation reaction is activated by large amounts of chloride and can be monitored spectrophotometrically by measuring the decrease in the absorbance of MB at 746 nm. The determination of bromide is performed by a fixed-time method at the first 100 s from the initiation of the reaction. Unlike other kinetic-spectrophotometric methods for the determination of bromide, the proposed method does not require heating the solution. Bromide can be determined in the range from 80 to 960 microg l(-1) with the detection limit of 35 microg l(-1). The relative standard deviation of ten replicate determination of 480 microg l(-1) bromide was 1.4%. The influence of potential interfering ions was studied. The proposed method was satisfactorily applied to the determination of bromide in seawater without interfering effect from chloride ion.