Immobilized Activated Carbon as Sorbent in Solid Phase Extraction with Cold Vapor Atomic Absorption Spectrometry for the Preconcentration and Determination of Mercury Species in Water and Freshwater Fish Samples.

A new preconcentration method using solid phase extraction (SPE) was developed by immobilizing dithizone (DZ) and 1,4-diphenylsemicarbazide (DPC) on oxidative activated carbon and then using this for the speciation and preconcentration of mercury species (Hg(II) and MeHg(I)) by flow injection cold vapor atomic absorption spectrometry (FI-CVAAS). The SPE experimental conditions were investigated including pH, amount of adsorbent and flow rate. The elution parameters and effect of foreign ions were also elucidated. Under the optimized conditions, the calibration graph was linear in the ranges of 0.015 - 3.0 µg L-1 of Hg(II), with a detection limit (LOD) of 0.0155 µg L-1, corresponding to three times the standard deviation (3SD, n = 20). The precision of the method, defined as percentage relative standard deviation (%RSD) for mercury was 1.25 - 3.79% at concentrations of 0.1 - 1.0 µg L-1, for which a preconcentration factor of 20 was obtained for Hg(II). The proposed method was validated by determining the mercury concentration in standard reference materials, and successfully applied to the speciation of mercury in several water and freshwater fish samples.

Speciation of mercury in water and freshwater fish samples by a two-step solidified floating organic drop microextraction with electrothermal atomic absorption spectrometry.

A new and simple two-step SFODME using 4-nitro-o-phenylenediamine (4-NOPD) as a chelating agent was developed for mercury speciation in water and fish samples by ETAAS. For the first step, methylmercury was extracted into 1-undecanol and for the second step, the Hg(II) remaining in the sample solution was complexed with 4-NOPD and then extracted into 1-undecanol. Under the optimized conditions, the calibration graphs of Hg(II) and methylmercury were linear in the range of 0.83-8.0 µg L-1 and 0.78-8.0 µg L-1, with the LOD of 0.25 µg L-1 and 0.24 µg L-1 and the enrichment factor were 25.7 and 32.2, respectively. The %RSDs was in the range of 2.0-4.4% at concentrations of 0.5 and 4.0 µg L-1 (n = 5). The proposed method was successfully applied to mercury speciation in water and fish samples. The accuracy of method, tested by the analysis of SRM 1566b and DORM-4 was in good agreement with the certified values.

Surfactant-assisted emulsification dispersive liquid-liquid microextraction using 2-thenoyltrifluoroacetone as a chelating agent coupled with electrothermal atomic absorption spectrometry for the speciation of chromium in water and rice samples.

A novel method was developed by SAE-DLLME for chromium speciation in water and rice samples using 2-thenoyltrifluoroacetone (TTA) as a chelating reagent by ETAAS. The speciation of Cr(III) and Cr(VI) was achieved by complexation of Cr(III)-TTA and the total Cr was measured after reduction of Cr(VI) to Cr. The calibration graph was linear in the range of 0.02-2.50 µg L-1, with a detection limit of 0.0052 µg L-1. The %RSD was in range of 2.90-3.30% at 0.5, 1.5 and 2.5 µg L-1 of Cr(III), n = 5 and the EF was 54.47. The method was applied to chromium speciation and total chromium determination in real samples and gave recoveries in the range of 96.2-103.5% and 97.1-102.7% for Cr(III) and Cr(VI) in water samples and 93.7-103.5% of total Cr in rice samples. The accuracy of the method was evaluated by analysis of SRM 1573a with good agreement compared to the certified value.

Determination of cadmium in herbs by SFODME with ETAAS detection.

A method for the determination of cadmium in herb samples based on solidified floating organic drop microextraction (SFODME) using 1-(2-Pyridylazo)-2-naphthol (PAN) as a chelating reagent and detection by electrothermal atomic absorption spectrometry (ETAAS) was developed in the present work. The effects of pH, extraction solvent, extraction time, stirring rate, and extraction temperature were investigated. Under the optimized conditions, the calibration graph was linear in the range of 0.017-3.0µgL-1, with a detection limit (LOD) of 0.0052µgL-1. The relative standard deviation (%RSD) for 6 replicate measurements of 1.0µgL-1 cadmium was ±2.67%. The method was applied to the analysis of 10 types of Thai herb samples. Percentage recoveries were in the range 94.5-110.2%. It was found that cadmium concentrations in all Thai herb samples were less than the maximum residue level.