A new spectrophotometric method was developed for the determination of low ppb levels of arsenic in water. We found that Ethyl Violet with molybdate-iodine tetrachloride complex forms nanoparticles under acidic conditions, which provide a sensitive probe for molybdoarsenate. The nanoparticles form stable particles with a diameter micrometers in size in the presence of heteropolyacid, and the resulting particles give a purple color to the apparently homogeneous solution, the intensity of which depends on the arsenic concentration. The nanoparticle itself is unstable due to conversion of the dye to a colorless carbinol species under acidic conditions without heteropolyacid. Although triphenylmethane dyes have been the subject of a number of investigations, there do not appear to be any reports on the dye particles for trace determination. The calibration curve is linear up to 20 microg L-1 arsenic, and the detection limit is 0.5 microg L-1 (6.6 x 10(-9) mol L-1). The coefficient of variation for spectrophotometry at 10 microg L-1 is 5.8% (n = 8). Furthermore, it is possible to detect concentrations as low as 1 microg L-1 arsenic visually using this method. The interferences from phosphorus and silica were eliminated using an anion exchange column and sodium fluoride as a masking agent, respectively. The proposed method has been successfully applied to water samples in abandoned mine water, groundwater, and river water. There was good agreement between the results obtained by the proposed method and those by hydride generation atomic absorption spectrometry. Since this method is specific for As(V), it is applicable to the speciation of arsenic oxidation states. Our method has enormous practical potential for simple and field detection of arsenic, requiring no complex apparatus or skilled laboratory support.
In this study, a simple and sensitive method for the determination of arsenic in water samples was developed. The method is based on the formation of micro particles of Ethyl Violet and molybdoarsenate, which gives an apparently homogeneous blue color to the solution. The absorption of the excess dye gradually decreases due to its conversion to a colorless carbinol species under strongly acidic conditions. Consequently, the sufficiently low reagent blank enables the spectrophotometric determination of arsenic with the detection limit of 4 μg l -1 . The coefficient of variation for the spectrophotometry at 50 μg l -1 was 3.5% (n = 5). Furthermore, it is possible to detect concentrations as low as 10 μg l -1 of arsenic visually. Our method will be useful as a simple, rapid, and cost-effective field test of arsenic, requiring no complex apparatus or skilled laboratory support.
By constructing a self-ordered nearly perfect ring system, a new type of visual test method has been developed. Poly(vinyl alcohol) forms a sharp ring–like solid phase (10.6 mm diameter) when a 100-μl drop of its aqueous solution was evaporated on a poly(vinyl chloride) plate. Aluminium ion of 1 – 30 ppb has been determined visually as a fluorescent 1:1 chelate of 2,2′-dihydroxyazobenzene concentrated into the ring.
An ion-pair reversed-phase partition high-performance liquid chromatography-spectrophotometric method is described for the determination of aluminum in human serum, based on its complexation with 2,2'-dihydroxyazobenzene. The chelate is separated on C18-bonded silica packing by using an aqueous methanol mobile phase containing tetrabutylammonium bromide and is detected with 0.005 AU full-scale at 510 nm. The proposed system offers a simple, sensitive, and selective method. The detection limits defined as twice the standard deviation of the blank signal, are 0.2 micrograms L-1 in pure solution and 6 micrograms L-1 in serum. The sample solution is prepared from 0.4 mL of serum after protein precipitation with hydrochloric acid and methanol. There was good agreement between the values obtained by this method and graphite furnace atomic absorption spectrophotometry. The aluminum concentrations in 121 patients on hemodialysis were 6-201 micrograms L-1.
The anionic chelate of iron(III)-2,2'-dihydroxyazobenzene (H2L), [FeL2]-, formed 1 : 1 ion-pair with crystal violet cation (CV +), CV + [FeL2]-, and was adsorbed on a surface of transparent polyvinyl chloride (PVC) film plasticized with di-n-octyl phthalate. Enrichment of the blue violet species of the ion-pair onto the transparent PVC film has enabled a highly sensitive and simple method for the determination ofiron(III). The detection limits are i x 10 -8 mol dm -3 (0.6 ppb) by spectrophotometry at 592 nm, and 4 x 10 -8 tool dm -3 (2 ppb) by visual colorimetry. The method has been successfully applied to the determination of iron in water samples and human serum. No preparatory procedures for the separation of serum protein and other coexisting substances are required, since ion-pair adsorption process provides a new method to prevent interference of serum matrix.
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