Microwave-Induced Combustion in Disposable Vessels: A Novel Perspective for Sample Digestion

Abstract

A novel system for sample digestion was proposed based on microwave-induced combustion in disposable vessels (MIC-DV) for trace elements determination by inductively coupled plasma optical emission spectrometry (ICP-OES). As a proof of concept, botanical samples were digested by MIC-DV for further determination of Al, Cr, Cu, Fe, Mn, Sr, and Zn. The system consists of a quartz holder (a modified version of conventional MIC) placed inside disposable polypropylene (PP) vessels. The quartz holder was carefully designed to avoid excessive heating and damaging of the vessel walls. For the combustion, the PP vessels containing the quartz holder and sample were placed in a specially designed metallic rotor that prevents the heating of absorbing solution and allows the use of a domestic microwave oven for sample ignition. After combustion, the digestion vessel was shaken to ensure the analytes’ absorption. The single-vessel principle was fulfilled, since no further dilution or liquid transfer was required and the same PP vessel used for digestion allowed solution storage until element determination. The influences of absorbing solution (diluted HNO3 and water) and sample mass (10 to 30 mg) were evaluated. By using the proposed MIC-DV system, low volumes of diluted absorbing solutions (5 mL of 1 mol L–1 HNO3) were possible, allowing the use of low reagent amounts and low energy consumption, since microwave irradiation is used only for sample ignition. The agreement with certified values ranged from 92 to 108% for all analytes, whereas the precision was below 15%. All of these advantages, combined with the use of low-cost disposable vessels and instrumentation, make MIC-DV suitable to be used for research and routine analysis.

High-Resolution Detection of Rock-Forming Minerals by Permittivity Measurements with a Near-Field Scanning Microwave Microscope

“…From the petrographic analysis shown in Figure 6 a, it was possible to correlate the rock’s mineral composition with the measured permittivity. First, we found a large quantity of quartz mineral, a material commonly employed as a microwave inert element for microwave processing applications [ 75 ]. In these areas, the dielectric constant was around 4 with loss factor values below 10 −2 , which indicated the low capacity of quartz to absorb microwave energy as exhibited in the heating experiments reported in [ 76 ] and in other related reports [ 70 ].…”