This paper presents a study involving the development of a new mini polytetrafluoroethylene (PTFE) vessel project for biological sample preparation in micro scale in closed system with microwave radiation for subsequent determination of Cd, K, Mg and Na by atomic spectrometry techniques. All experiments were carried out in micro quantities of samples (up to 20 mg) and reagents (300 µL of HNO3) for 5 min at 350 W. Certified reference materials of biological samples (bovine muscle and liver) were used to evaluate the accuracy of the proposed system and the results obtained were in agreement with the certified value at 95% of confidence (t -test). Relative standard deviations (RSD) were lower than 8.0% for all elements. The proposed method is not only easy and fast, but it is also based on the use of an inexpensive system for sample digestion.

In the first part of this paper, two acid decomposition procedures for the determination of Al, Ca, Fe, Mg, Mn and Zn contents in yerba mate samples by inductively coupled plasma optical emission spectrometry (ICP OES) were compared. Using a reflux system, the samples were treated with a mixture of HNO3 and H2O2 for 3 hours at 220 °C in the digester block. The results from five commercial yerba mate samples were compared with the results obtained from microwave digestion. Good agreement between the procedures at a 95% confidence level was obtained with relative standard deviation (RSD) values lower than 10.0%. The accuracy was evaluated using addition and recovery experiments (80.5 to 112.8%). In the second part, Ca, Cd, Cr, Cu, Fe, K, Mg, Na, Pb and Zn concentrations were evaluated in the yerba mate infusion. The results showed that elements such as Na, K, Mg and Zn are easily transferred to the hot water used for the infusion. For Pb and Cd, the concentrations found in the analyzed samples were lower than the values established by Brazilian legislation.

This paper describes the evaluation of a method for determination of Cd and Pb in xanthan gum samples by Graphite Furnace Atomic Absorption Spectrometry (GF AAS) using NH4H2PO4 as the chemical modifier. The sample preparation was performed using a reflux system adapted in the digestion tubes. With this system it was possible to increase the temperature of the digester block above the boiling point of the reaction medium, preventing loss of analyte and excessive evaporation of acids during heating. Samples were digested with HNO3 for 3 h in a digester block at 220 ºC. The limits of detection for Cd and Pb were 2.2 and 33.8 ng g-1, respectively. The RSDs for both analytes were, on average, lower than 5.0% and accuracy was verified by recovery tests, yielding values in the 83-100% range.