Determination of Halogens in Coal after Digestion Using the Microwave-Induced Combustion Technique

Abstract

The microwave-induced combustion (MIC) technique was applied for coal digestion and further determination of bromide, chloride, fluoride, and iodide by ion chromatography (IC). Samples (up to 500 mg) were combusted at 2 MPa of oxygen. Combustion was complete in less than 50 s, and analytes were absorbed in water or (NH(4))(2)CO(3) solution. A reflux step was applied to improve analyte absorption. Accuracy was evaluated for Br, Cl, and F using certified reference coal and spiked samples for I. For Br, Cl, and F, the agreement was between 96 and 103% using 50 mmol L(-1) (NH(4))(2)CO(3) as the absorbing solution and 5 min of reflux. With the use of the same conditions, the recoveries for I were better than 97%. Br, Cl, and I were also determined in MIC digests by inductively coupled plasma mass spectrometry, inductively coupled plasma optical emission spectrometry, and F was determined by an ion-selective electrode with agreement better than 95% to the values obtained using IC. Temperature during combustion was higher than 1350 degrees C, and the residual carbon content was lower than 1%. With the use of the MIC technique, up to eight samples could be processed simultaneously, and a single absorbing solution was suitable for all analytes and determination techniques (limit of detection by IC was better than 3 microg g(-1) for all halogens).

Feasibility of ultra-trace determination of bromine and iodine in honey by ICP-MS using high sample mass in microwave-induced combustion

“…In this work, Br and I absorption experiments were evaluated using 25, 50, 75, 100, and 150 mmol L −1 (NH 4 ) 2 CO 3 or NH 4 OH because these solutions were recommended for halogen absorption after decomposition by MIC [38,39]. Experiments were carried out by adding the equivalent of 0.3 and 0.045 μg of Br and I, respectively, to honey sample (1000 mg), prior to the combustion.…”

“…Microwave-induced combustion (MIC) has been successfully applied for the decomposition of organic samples for further determination of halogens owing to the high efficiency of matrix oxidation and the possibility of using alkaline solutions for analyte absorption [17][18][19][20][21][22][23][24][25][26][27]. In this method, solid samples are generally prepared as pellets and positioned on a quartz holder, and combustion is performed inside a quartz vessel pressurized with oxygen, using microwave radiation and ammonium nitrate solution for the ignition step.…”

Spatial variation in natural formation of chloroform in the soils of four coniferous forests

“…The conditions during the MICprocedure were as follows: Triplicate soil samples (about 200 mg) were pressed as pellets using a hydraulic press set at 3 ton for 1 min for further digestion by MIC. Conditions were chosen according to previous work (Flores et al 2008) using 6 mL of 50 mM (NH 4 ) 2 CO 3 as absorbing solution. The heating program was 1400 W for 10 min (reflux step) and 0 W for 20 min for cooling.…”

Analytical methods for the determination of halogens in bioanalytical sciences: a review

“…A few microliters of ammonium nitrate is added to the filter paper to aid combustion [58,118]. MIC has been applied for many analytes and matrices such as food [58,111,120,121], botanical samples [83,86,122,123], soil [124], and petroleum-related matrices [125][126][127][128][129][130][131]. Dilute alkaline solutions are required to ensure quantitative recoveries for halogens when using MIC and to avoid losses, especially for bromine and iodine [58,91].…”