DEVELOPMENT OF A NEW DEVICE BASED ON MONOMODE MICROWAVE FOR SOLID SAMPLE INTRODUCTION IN FLAME FURNACE ATOMIC ABSORPTION SPECTROMETRY

Flame atomic absorption spectrometry (F AAS) is a widespread technique used for elemental determination. The robustness and relative low cost makes F AAS attractive for routine analysis. However, it presents some limitations especially regarding to sensitivity and limit of detection (LOD), being a limitation of this technique when looking for trace analysis. Microwave-induced combustion (MIC) was proposed and successfully applied for decomposition of many kinds of samples for both metals and nonmetals determination. In previous works, MIC method was coupled to flame furnace atomic absorption spectrometry (MIC-FF-AAS). With this combination direct analysis of solid samples was performed, making not necessary a sample preparation step previously to the analysis, and thus improving the LODs. However, a domestic microwave oven was used, which was not well designed for laboratory routine. In order to overcome this and other limitations, in the present work a new device based on monomode microwave applicator was developed and applied for direct analysis of solid samples by MIC-FF-AAS. This system consists of a quartz tube located inside of a metallic waveguide placed immediately in front of the spectrometer atomizer. With this modification, the path of the gaseous products originated during sample combustion was reduced, minimizing the risks of analyte loss due condensation. As an example, cadmium was determined in polymers samples in order to demonstrate the potential of the proposed system. Samples were weighed directly on a quartz boat, containing a small piece of filter paper wetted with 6 mol/L ammonium nitrate solution, and it was introduced into the microwave system for inducing sample combustion. Oxygen was continuously introduced into the quartz tube to as an aid for the sample combustion, as well as to carry combustion products to the atomizer. Microwave radiation was kept on until the sample ignition. After that, microwave radiation was stopped and atomic absorption signals were recorded. The calibration using aqueous reference solutions and some operational conditions such as igniter volume, oxygen flow rate, FF tube design, flame stoichiometry, and sample mass were evaluated. The proposed combustion system is portable and might be easily adapted to any conventional atomic absorption spectrometer, increasing the range of applications of this well-known technique.