Speciation and detection of arsenic in aqueous samples: a review of recent progress in non-atomic spectrometric methods.

Arsenic contamination of drinking water is a major global problem, with contamination in Bangladesh deemed most serious. Although the current World Health Organisation (WHO) maximum contamination limit (MCL) for arsenic in drinking water is 10 μg L−1, due to practical and economic constraints, the standard limit in Bangladesh and many other developing nations is 50 μg L−1. We propose that an ideal arsenic sensor, designed for routine monitoring, will have five essential qualities: sensitivity and selectivity for arsenic; speed and reliability; portability and robustness; reduced health and environmental risks; and affordability and ease of use for local technicians. It is our opinion that many of these characteristics can be accentuated by microfluidic systems. We describe candidate colorimetric, electrochemical, biological, electrophoretic, surface-sensing, and spectroscopic methods for arsenic detection; and comment on their potential for portable microfluidic adaptation. We also describe existing developments in the literature towards the ultimate creation of microfluidic total analysis systems (μTASs) for arsenic detection. The fundamental purpose of this review is to highlight the need for better portable arsenic contamination detection, and describe how microfluidic technology may be developed to address this need.

Detection of trace arsenic in drinking water: challenges and opportunities for microfluidics

Nano-Enabled sensors for detection of arsenic in water

Arsenic, a common contaminant of groundwater, affects human health adversely. According to the World Health Organization (WHO), the maximum recommended contamination level of arsenic in drinking water is 10 μg/L. The purpose of this research was to develop user-friendly kits for detection of arsenic to measure at least up to 10 μg/L in drinking water, so that a preventive measure could be taken. Two different kits for detection of total arsenic in water are reported here. First, the arsenic in drinking water was converted to arsine gas by a strong reducing agent. The arsine produced was then detected by paper strips via generation of color due to reaction with either mercuric bromide (KIT-1) or silver nitrate (KIT-2). These were previously immobilized on the detector strip. The first one gave a yellow color and the second one grey. Both of these kits could detect arsenic contamination within a range of 10 μg/L-250 μg/L. The detection time for both the kits was only 7 min. The kits exhibited excellent performance compared to other kits available in the market with respect to detection time, ease of operation, cost and could be easily handled by a layman. The field trials with these kits gave very satisfactory results. A study on interference revealed that these kits could be used in the presence of 24 common ions present in the arsenic contaminated water. Though the kits were meant for qualitative assay, the results with unknown concentrations of real samples, when compared with atomic absorption spectrophotometer (AAS) were in good agreement as revealed by the t-test.

Low-cost field test kits for arsenic detection in water

The present work reports on a polymer hydrogel-based cost effective colorimetric dipstick sensor for arsenic(V). The method was based on the formation of a blue colored antimonyl–arseno–molybdate complex in the presence of ammonium molybdate, potassium antimonyl tartrate and ascorbic acid. All these reagents were encapsulated in a polymer hydrogel made of polyvinyl alcohol, acrylamide and glutaraldehyde. Plastic detector strips were dip coated with this hydrogel. Scanning electron microscopy (SEM) depicted the highly porous structure of the polymer hydrogel permitting adsorption of As(V) confirmed by energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) analysis. The advantages were low sample volume (10 ml), low detection limit (10 μg L−1 by the naked eye), good stability (4 months), low cost (0.03$ per test for visual detection), and high reproducibility. The sensor strips displayed selectivity in the presence of <100 μg L−1 of phosphate (arsenate structural analog) and 3 mg L−1 of iron. Changes in the RGB (red, green, and blue) values of color spots on the As(V) colorimetric dipstick sensor with various concentrations of As(V) created a pattern. The dominance of B (blue) values was revealed in low concentration range of As(V) while the R (red) values dominated in higher concentrations. The same strip could be used for detection of total arsenic in case the sample contained As(III). Phosphate interference could also be detected by a simple modification of the procedure. When applied to real groundwater arsenic contaminated samples, the results were in good agreement with the atomic absorption spectrophotometry (AAS) results as visualized by statistical analysis.

A new dipstick colorimetric sensor for detection of arsenate in drinking water

A method for determination of arsenic is described. The sensor was constructed by immobilizing reagents on TLC (thin layer chromatography) paper. The reaction is based on chromogenic reaction of arsenic with a coupling complex of sulfanilic acid and N-(1-naphthyl) ethylene diamine dihydrochloride (NEDA) and formation of purple to magenta spots followed by scanner based detection. Changes in RGB values of color spots on TLC strips create a pattern. The obtained pattern was analyzed using MATLAB software. The proposed sensor is linear in the range 1–10 and 25–100 μg mL −1. The minimum detection limit found was 0.018 μg mL−1of arsenic.

MATLAB assisted disposable sensors for quantitative determination of arsenic

The proposed method describes the use of paptode for determination of diphenylamine. The method describes chemo sensors developed for the determination of diphenylamine. The method is based on the reaction of diphenylamine with ninhydrin gives an iminium salt, on heating which formed orange color dye in acidic medium. The color system formed particular pattern on an inert support. Scanner detects the product on TLC strips and obtained pattern analyzed with program written in visual basic 6.0 (VB6). The proposed sensor is linear in concentration range 0.3- 5.1 μg/ml. All the analytical parameters and optimum reaction conditions was evaluated. The sensors are used to detect diphenylamine in real sample i.e. fruits and milk.

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Disposable sensors for the determination of diphenylamine with ninhydrin as a choromogenic reagent

A new optical analytical method, "digital RGB Analysis" is proposed based on MATLAB image processing tool instead of the conventional optical method, "spectrophotometry". MATLAB image processing tool can transform the color information into digital RGB values that can be treated as analytical information. Image processing tool can simulate the optimum color variations by optimization of visual color sensor with computer assistance and thus make colorimetry (semi quantitative analysis) as an accurate determination method. The optode was constructed by immobilizing ninhydrin on TLC (thin layer chromatographic) paper. The reaction is based on complexation of ninhydrin with cadmium to result into a light purple to magenta colored spot followed by scanner based detection. Changes in RGB values of color spots on TLCstrips create a pattern. The obtained pattern was analyzed using image processing tool of MATLAB software to determine cadmium. All parameters affecting intensity on optode have been optimized. The proposed sensor was linear in the range 0.018-0.54µg mL -1 (R 2 =0.996) for G values and can sense up to 3ng mL -1 .SEM investigation of dye has also been done.The proportionality in intensity of the spot color on the optodes loaded with varying amounts of cadmium suggests its potential applications for determination of it in various samples. The paper optode can be used for pollutant check and even health check at home. Thus the paper optode has great potential for this purpose.

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Cadmium Ion Sensing Paptode Based On Digital RGB Color Analysis

Determination of arsenic through a new reagent system has been described here. The method is based on reduction of sulfanilic acid by arsenic and subsequent coupling with N-(1-naphthyl) Ethylene diamine dihydrochloride (NEDA) in aqueous medium. The dye formed shows maximum absorbance at 550nm. The detection limit of arsenic is 0.015ppm, the method obeys BeerÂÂs Law in the range 0.1-0.6ppm. The molar absorptivity was found to be 2.53x104Lmol-1cm-1. SandellÂÂs sensitivity, standard deviation and relative standard deviation were found 5.24x10-4, 0.023 and 1.48 % respectively. The method is free from most of the interferences. The method was successfully applied for the determination of arsenic in various environmental samples, plant, pharmaceutical tablet and biological samples. The method is utilized for developing sensing devices for detection of arsenic.

Sulbha Amlathe

Papers

MATLAB assisted disposable sensors for quantitative determination of arsenic

Disposable sensors for the determination of diphenylamine with ninhydrin as a choromogenic reagent

Cadmium Ion Sensing Paptode Based On Digital RGB Color Analysis

Quantitative determination and development of sensing devices via a new reagent system for arsenic