Microwave-induced combustion coupled to flame furnace atomic absorption spectrometry for determination of cadmium and lead in botanical samples.

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.