Ultra-trace determination of cadmium in water and food samples by a thin-film microextraction using a supported liquid membrane combined with smartphone-based colorimetric detection.

A mixture of n-octanol and dithizone was introduced as an effective and novel extraction agent in a thin-film microextraction technique for the pre-concentration of cadmium ions. The extraction agent was immobilized on small pieces of porous polypropylene flat membrane as a supported liquid membrane. The analyte extraction was performed by immersing the modified film in the sample solution, and via a complex formation between the immobilized dithizone on the film and cadmium ions. After the thin-film microextraction process, the colored cadmium-dithizone complex was directly measured by a smartphone colorimetric analysis. Under optimized conditions, the linear dynamic range, the limit of detection, and the limit of quantification were 0.5-300.0, 0.1, and 0.4 µg L-1, respectively. The developed technique was successfully employed to quantify cadmium ions in water and food samples. The high relative recovery values (95.0-103.0%) along with relative standard deviations of less than 2.5% were obtained for the spiked samples.

Plasma jet desorption atomization-atomic fluorescence spectrometry and its application to mercury speciation by coupling with thin layer chromatography.

A novel plasma jet desorption atomization (PJDA) source was developed for atomic fluorescence spectrometry (AFS) and coupled on line with thin layer chromatography (TLC) for mercury speciation. An argon dielectric barrier discharge plasma jet, which is generated inside a 300 µm quartz capillary, interacts directly with the sample being analyzed and is found to desorb and atomize surface mercury species rapidly. The effectiveness of this PJDA surface sampling technique was demonstrated by measuring AFS signals of inorganic Hg(2+), methylmercury (MeHg), and phenylmercury (PhHg) deposited directly on TLC plate. The detection limits of the proposed PJDA-AFS method for inorganic Hg(2+), MeHg, and PhHg were 0.51, 0.29, and 0.34 pg, respectively, and repeatability was 4.7%, 2.2%, and 4.3% for 10 pg Hg(2+), MeHg, and PhHg. The proposed PJDA-AFS was also successfully coupled to TLC for mercury speciation. Under optimized conditions, the measurements of mercury dithizonate (Hg-D), methylmercury dithizonate (MeHg-D), and phenylmercury dithizonate (PhHg-D) could be achieved within 3 min with detection limits as low as 8.7 pg. The combination of TLC with PJDA-AFS provides a simple, cost-effective, relatively high-throughput way for mercury speciation.

Screening for mercury in aqueous environmental samples and urine samples using thin layer chromatography.

A method for screening based on thin layer chromatography (TLC) comprising silica gel 'G' as a stationary phase and benzene as a mobile phase was found to be most suitable for the detection of mercury in aqueous samples and spiked human urine, without digesting the samples. A broad range for the detection of mercury, from 20 microg/L (20 ppb) to 1000 mg/L (1000 ppm), was established, by optimizing the experimental conditions. In urine samples, mercury could be detected also, at levels as low as 50 microg/L (50 ppb) or above. Mercury was detected by complexation with dithizone followed by TLC, also in the presence of other heavy metals, including arsenic, cadmium, lead, copper, iron, zinc, and nickel. The method is simple, cheap, and has no interference of the matrix present in the natural water and aqueous industrial effluent samples obtained from the field. Further, no sophisticated instrument is needed for the detection of mercury.

Improved signals ratio resolution method by optimization of resolution function--simultaneous determination of Cu(II) and Cd(II) in water samples.

From an ecological and economical point of view, it is important to design analytical procedures for monitoring heavy metals in the environment and industrial processes in a way to minimize the use of hazardous reagents and reduce the analysis time. In this paper, a well-known dithizonate extraction-based method for the determination of many metal ions was improved by using chemometrical selectivity of the strongly overlapped spectra of copper and cadmium dithizonates in CCl4 for their simultaneous determination from a single extraction at pH 10. The individual absorption spectra, having absorption maxima difference of only 20 nm, were separated, and the metal ions were quantified by using an improved procedure for optimizing the resolving function in a recently proposed signals ratio method. The procedure consists of using many different resolving functions and plotting the difference of the mean of absolute and nonabsolute mean values of pseudosignals [PDMMV (PS)] against analyte concentrations obtained with each of the resolving functions, thus obtaining 2 straight lines having intersections that give a unique and reliable value of the unknown concentration of the individual analyte in mixture giving strongly overlapped spectra. In this way, the main drawback of the signals ratio resolution method, that is, the visual estimation of optimal resolving function, is eliminated. The proposed parameter, PDMMV (PS), was tested by using both simulated and experimental spectra. Copper was determined in the mixture with ca 20-fold excess of cadmium, and cadmium was determined in ca 10-fold excess of copper at submicromolar concentration levels.

Generalized theory for two-phase ion-pair and complexometric titrations. II. Two-phase titrations with side reactions.

For the two-phase titration based on ion-pair and metal-complex formation full attention is given to side reactions in both phases. Their significance for the applicability of this type of titration is evaluated. Side reactions in the aqueous phase diminish and in the organic phase promote the 'titratability'. Equations for the calculation of the side reaction coefficients, the titration curve and the selection of the optimal pH and minimal side reaction interference (in the aqueous phase) are presented. Finally a full description is given of the two-phase titration including all parameters determining the 'titratability'. The merits of the developed theory are illustrated by literature examples.

Agua potable. Determinación del mercurio por el método de la ditizona / Drinking water. Determination of the mercury by the method of the ditizona

Esta norma tiene por objeto la determinación del mercurio en agua potable por el método de la ditizona,es aplicable a aguas en general.

Agua potable. Determinación del plomo por el método de la ditizona / Drinking water. Determination of the lead by the method of the ditizona

Esta Norma establece el método para la determinación del plomo por extracción con ditizona, es aplicable a aguas potables como también para aguas negras y aguas de desechos industriales.

Agua potable. Determinación del zinc por el método de la ditizona / Drinking water. Zinc determination by the method of the ditizona

Esta norma establece el método para la determinación del Zn (cinc) por el método de la Ditizona, es aplicable a aguas en general.

Decomposition of thimerosal in aqueous solution and its determination by high-performance liquid chromatography.

Studies on the decomposition of thimerosal in aqueous solution have confirmed that thiosalicylic acid and ethylmercuric hydroxide are the initial products. On prolonged reaction, thiosalicylic acid was oxidized to 2,2'-dithiosalicylic acid, while ethylmercuric hydroxide was reduced to elemental mercury. As a result, a specific, reverse-phase high-performance liquid chromatographic assay has been developed for thimerosal in the presence of its decomposition products. By comparison, an existing colorimetric assay procedure employing dithizone was shown to be not fully specific. The presence of sodium chloride in the solution accelerated the decomposition of thimerosal. There was evidence that thimerosal was sorbed onto plastic containers on storage.