A novel digestion procedure based on sample combustion ignited by microwave radiation is proposed for organic samples. Certified samples of bovine liver, pig kidney, and skim milk were used as examples to demonstrate the performance of the proposed procedure. Cadmium and copper were determined in these samples by electrothermal atomic absorption spectrometry. Samples (between 50 and 250 mg) were wrapped with paper and placed on a homemade quartz holder that was positioned inside to quartz vessels used in a commercial microwave oven. Ammonium nitrate solution was added to the paper, and vessels were pressurized with oxygen to 15 bar. The rotor containing four vessels was placed inside the oven, and microwave radiation was applied for 20 s at 1400 W. Combustion was complete in few seconds, and an additional reflux step, which was optional, was applied. The agreement to the certified values was between 96 and 105% for both analytes. Only with the combustion step, the residual carbon (RC) was below 1.3%. The RC decreased to less than 0.4% when an additional reflux step with concentrated nitric acid was applied.

No abstract

No abstract

É proposto um método para a determinação de fluoreto em carvão mineral. O mesmo é baseado no emprego da pirohidrólise para a separação do fluoreto da amostra e posterior determinação do analito por potenciometria direta, com eletrodo íon seletivo. O sistema utilizado para a realização da pirohidrólise foi desenvolvido e a influência do V 2 O 5 como catalisador na reação de pirohidrólise foi investigada, sendo verificado que o mesmo não influencia sobre a liberação do fluoreto presente na amostra. Amostras certificadas e não certificadas de carvão mineral foram analisadas. Resultados precisos (desvio padrão relativo inferior a 7%) e exatos (recuperação do fluoreto de acordo com os valores certificados) foram obtidos. O limite de quantificação (LOQ) do método foi de 5,0 µgF/g de amostra, usando 20 mg de amostra e volume final de 10 mL. A freqüência de análise foi de 5 amostras h -1 .A method for the determination of fluoride in coal using pyrohydrolysis for sample decomposition is proposed. An apparatus was constructed, and the influence of vanadium pentoxide (V 2 O 5 ) as a catalyst for the pyrohydrolysis reaction was investigated. It was verified that V 2 O 5 does not influence the release of fluoride from coal. Certified and non-certified samples were analysed using an ion selective electrode (ISE) for analyte detection. Precise (RSD < 7%) and accurate (recovery in accordance with certified values) results were obtained. The limit of quantification (LOQ) of the method was 5.0 µgF/g of sample, using 20 mg of sample and a final dilution to 10 mL. The sample frequency was 5 samples h -1 .Keywords: coal, fluoride, pyrohydrolysis, ion electrode, vanadium pentoxide, catalyst IntroductionFluorine is one of several trace elements receiving much attention owing to its possible harmful ecological effects. This element is considered essential to both plant and animal life at low concentrations but is toxic at high concentrations. The potential toxicity of fluorine has been classified as "high" for terrestrial life and "low" for aquatic life. 1,2 Due to the high volatility of the element, the widespread world consumption of coal may result in significant fluorine emissions. 2 From this point of view, it is important to establish accurate, precise and rapid methods for determination of this element.With the exception of a few instrumental methods, 2,3 the determination of fluoride in coal is carried out after sample dissolution. Most published methods related to the determination of fluoride in solid samples thus involve distillation, pyrohydrolysis, alkaline fusion, combustion bomb or acid decomposition in a bomb, typically followed by spectrophotometric or potentiometric measurements. 3,4 In some instances, these methods are complex and time consuming (mainly methods based on distillation and fusion), may give incomplete breakdown of fluorinecontaining compounds, analyte losses during the depressurisation of the bomb (decomposition in a combustion bomb), or by volatilisation (alkaline fusion), if the fusion temperature is...

A procedure for sample digestion based on focused microwave-induced combustion (FMIC) is proposed. This system was developed using a commercial focused microwave oven with a lab-made quartz sample holder and a modified glass vessel. Oxygen flow was used to start and support the combustion. A botanical sample was used to evaluate the operational conditions for further Al, Ba, Ca, Fe, Mg, Mn, Sr, and Zn determination by inductively coupled plasma optical emission spectrometry. Pelletized samples were positioned on the quartz holder, and 50 microL of 6 mol L(-1) NH(4)NO(3) solution was added as igniter. Combustion was completed in less than 2 min, and the temperature was higher than 950 degrees C. The use of a reflux step, the position of sample holder inside the vessel, sample mass, ignition and combustion time, oxygen flow rate, and condenser type were evaluated. Results were compared with those obtained by focused microwave-assisted wet digestion and by high pressure microwave-assisted wet digestion. Agreement of 95-103% was obtained for certified reference materials digested by FMIC (reflux step with 10 mL of 4 mol L(-1) HNO(3)). With the proposed procedure, a complete sample decomposition (residual carbon content lower than 0.5%) was achieved with low consumption of reagents as only 10 mL of diluted nitric acid was necessary. Low relative standard deviation (lower than 3.8%) was observed and high amount of sample (up to 1500 mg) could be digested that allowed lower limits of detection.

In this work, sample preparation methods for polymer digestion based on microwave-induced combustion (MIC) and microwave-assisted acid digestion (MW-AD) were evaluated for further As, Bi,

A procedure based on microwave-induced combustion coupled to flame furnace (FF) atomic absorption spectrometry (FF-AAS) was used for analysis of solid samples. Botanical samples were prepared as pellets and introduced into a quartz holder device. This device was fitted to a glass chamber that was used for the combustion step. The complete device was coupled to the flame furnace by using poly(tetrafluoroethylene) and quartz tubes. The glass chamber was placed inside a microwave oven in a position previously set to receive the higher power of microwave radiation. Ignition was performed by microwave radiation using a small piece of paper wetted with NH4NO3 solution. An oxygen flow was used to assist the sample combustion and also to transport the combustion products up to the heated FF positioned above an air/ acetylene burner. Flame furnace temperature, oxygen flow rate, flame stoichiometry, and sample mass range were evaluated. Cadmium and lead were determined in botanical samples as examples to demonstrate the potential of the proposed procedure for trace analysis. Sample masses up to 60 mg could be used, allowing a limit of detection as low as 0.003 and 0.24 microg g(-1) for Cd and Pb, respectively. Integrated absorbance was used with an integration time of 30 s. Background signals were always low, and relative standard deviation (n = 5) was below 9% for Cd and 11% for Pb. The throughput was 20 determinations/h, including the weighing step. Accuracy was between 94 and 105%, and calibration was performed using standard solutions. The combustion device could be easily adapted to conventional atomic absorption spectrometers.

No abstract