Microwave-Induced Combustion Coupled to Flame Furnace Atomic Absorption Spectrometry for Determination of Cadmium and Lead in Botanical Samples Juliano S. Barin, Fabiane R. Bartz, Valderi L. Dressler, Jose ´ N. G. Paniz, and E ´ rico M. M. Flores* Departamento de Quı ´mica, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS, Brazil A procedure based on microwave-induced combustion coupled to flame furnace (FF) atomic absorption spec- trometry (FF-AAS) was used for analysis of solid samples. Botanical samples were prepared as pellets and intro- duced 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 micro- wave radiation using a small piece of paper wetted with NH 4 NO 3 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 botani- cal 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 μgg -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 per- formed using standard solutions. The combustion device could be easily adapted to conventional atomic absorption spectrometers. Flame atomic absorption spectrometry (FAAS) is a widespread analytical technique that has been successfully applied to the determination of many elements in several kinds of samples. The robustness and relatively low cost made FAAS very attractive, and a great number of laboratories have currently used this technique for routine analysis. However, FAAS presents some limitations especially regarding the sensitivity and limit of detection (LOD) for some elements that make this technique unsuitable for trace analysis in many matrixes. One of main drawbacks is that samples should be introduced, preferentially as liquids by nebulization. In this process, the larger drops are drained off while the smaller ones are carried out up to the flame. Thus, the efficiency of conventional nebulization systems is poor and contributes to the low sensitivity observed because, in general, less than 10% of the solution reaches the atomizer. In addition, the analyte dilution with the flame gases also contributes for the relatively high LOD for FAAS. 1-3 Recently, a new method using a metallic tube heated by air/ acetylene flame was proposed to improve the sensitivity of FAAS. 4-6 In this system, called thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS), the liquid sample was transported through a flame-heated ceramic capillary producing a thermospray that was immediately introduced into a metallic tube (FF) positioned above an air/acetylene burner. The introduc- tion of the whole sample and the increase of analyte density in the optical path resulted in a significant improvement of LOD for many elements. 5 This procedure has been successfully applied for many samples and analytes. 7-11 However, despite the better LODs, the application for solid samples requires a previous off- line digestion or at least a dissolution step. Thus, some disadvan- tages related to the sample preparation step remain as analyte dilution, risks of losses/contamination, and low throughput. On the other hand, if solid samples could be directly analyzed or the analyte could be totally introduced into the FF, these disadvan- tages would be minimized and an increase in the sensitivity and also better LODs would be expected. Although flames are not particularly suitable for solid sample introduction, some attempts have been carried out to overcome * To whom correspondence should be addressed. Fax: + 55 55 3220 9445. E-mail: flores@quimica.ufsm.br. 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Chim. Acta 2004, 512, 329–337. Anal. Chem. 2008, 80, 9369–9374 10.1021/ac8015714 CCC: $40.75  2008 American Chemical Society 9369 Analytical Chemistry, Vol. 80, No. 23, December 1, 2008 Published on Web 11/01/2008