Literature study of microwave-assisted digestion using electrothermal atomic absorption spectrometry

Pressurized liquid extraction as a novel sample pre-treatment for trace element leaching from biological material

Pressurized liquid extraction (PLE), commonly used for organic compounds extraction, has been applied for trace element leaching from marine biological material in order to determine major and trace elements (Al, As, Cd, Co, Cu, Fe, Hg, Li, Mn, Pb, Se, Sr, V and Zn). The released elements by formic acid PLE have been evaluated by inductively coupled plasma-optical emission spectrometry (ICP-OES). Different variables, such as formic acid concentration, extraction temperature, static time, extraction steps, pressure, mean particle size and diatomaceous earth (DE) mass/sample mass ratio were simultaneously studied by applying an experimental design approach (Plackett-Burman design (PBD) and central composite design (CCD)). Results showed that the extraction temperature was statistically significant (confidence interval of 95%) for most of the elements (high metal releasing was achieved at high temperatures). In addition, formic acid concentration was also statistically significant (confidence interval of 95%) for metals such as Cd and Cu. Most of the metals can be extracted using the same PLE operating conditions (formic acid concentration of 1.0 M, extraction temperature at 125 degrees C, static time of 5 min, one extraction step, extraction pressure at 500 psi and DE mass/sample mass ratio of 2). Taking in mind PLE requirements at the optimised operating conditions (125 degrees C), a time of 6 min is needed to pre-heat the cell. Therefore, the PLE assisted multi-element leaching is completed after 12 min. Analytical performances, such as limits of detection and quantification, repeatability of the over-all procedure and accuracy, by analysing GBW-08571, DORM-2, DOLT-3 and TORT-2 certified reference materials, were finally assessed.

Preconcentration and separation of copper, zinc and cadmium by the use of 6-mercapto purinylazo resin and their application in microwave digested certified biological samples followed by AAS determination of the metal ions

6-Mercapto purinylazo resin has been used as solid phase extractor. Based on solid phase extraction, the present work describes the preconcentration and determination of copper, zinc and cadmium in certified biological samples after microwave-assisted digestion. The exchange capacity of the resin, the sorption and desorption of metal ions, and the effect of diverse ions have also been determined. The results show that the resin is highly selective for determination of these biologically significant metals. The method is simple, rapid and free from interferences and can be used routinely.

Application of focused-microwave wet digestion to the determination of trace metals in human gallstones by ICP/AES

We propose an analytical digestion method for trace metal determination (Co, Cr, Cu, Fe, Mn, Ni and Zn) in gallstones, in an attempt to facilitate detection of their origin. The method consists of sample digestion with HNO3 and H2O2 by means of focused microwave. Metals are quantified by inductively coupled plasma atomic emission spectroscopy. The effect of calcium concentration in the analytical solutions was studied. Cu, Fe, Mn and Zn were detected in all the samples analysed and the highest concentrations were obtained for Cu and Fe, especially in black-pigmented gallstones. The reproducibility in terms of %RSD, determined in the gallstones with the lowest metal content, was below 5% for Cu, between 10% and 15% for Mn and Zn and up to 25% for Fe.

Experimental designs in the optimisation of ultrasonic bath-acid-leaching procedures for the determination of trace elements in human hair samples by atomic absorption spectrometry

Experimental designs were used for the optimisation of acid-leaching procedures assisted by ultrasonic energy for the extraction of Ca, Cu, Fe, Mg, Mn and Zn from human hair samples. A Plackett-Burman 2(7) x 3/32 design for seven factors ([HNO3], [HCl], [H2O2], acid/oxidant solution volume, exposure time to ultrasounds, temperature of the ultrasonic bath and hair particle size) was used in order to choose the variables affecting the acid-leaching process. The variables [HNO3], [HCl] and temperature of the ultrasonic bath were found to be the most important parameters for the acid-leaching procedure, and these variables were optimised by a response surface design (central composite design 2(3) + star) which involved 16 experiments. Optimum values in the 3.7-4.2 M range were found for [HNO3], while optimum values between 3.0 and 3.5 M were found for [HCl]. The optimum temperature of the ultrasonic bath was between 80 and 90 degrees C. An acid digestion induced by microwave energy (details given) was used to obtain the total metal concentration and also for comparative purposes. Ca, Cu, Fe, Mg and Zn were measured by flame atomic absorption spectrometry (FAAS) using a conventional air/acetylene flame, while Mn was determined by electrothermal atomic absorption spectrometry (ETAAS) under optimised conditions. Two different reference materials, IAEA-085 International Atomic Energy Agency, Monaco) and NIES No. 13 (National Institute for Environmental Studies, Japan), with certified metal contents for some of the elements investigated, were used in order to verify the accuracy of the methods.