Microwave digestion unit

Mn(II) and Fe(II) were determined by differential pulse voltammetry (9, 30). The determinations were carried out within a few hours after sampling. Total dissolved and particulate Fe and Mn (after digestion of the particulate matter in a microwave digestion unit with HN03-HC1) were measured by flame or graphite furnace atomic absorption spectrometry. 

The particulate material from the sediment traps was digested in aqua regia in a microwave digestion unit. Fe, Mn, Zn, Ca, Cr, and Cu were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) P was determined by the molybdate spectrophotometric method (28). A sediment standard (NBS No. 1645) was used regularly to check the accuracy of the sediment digestion procedure. 

Total elemental concentrations-Total concentration of each metal in an unfiltered sample was determined after digestion. The unfiltered sample was carefully mixed, and a known amount (approximately 10 g) was weighed into the Teflon bomb of the microwave digestion system. Five milliliters of concentrated ( 36N) trace-metal grade nitric acid were added to each sample and the mixture was digested at high temperature and pressure in a microwave digestion unit... 

Figure 8. Photograph of the fully automated total Tc analyzer instrument in the laboratory. The labeled components are (A) robotic autosampler (B) microwave digestion unit (C) fluid handling components for sample injection, automated standard addition, sample acidification/digestion (D) separation fluidics including syringe pumps, flow reversal, and diversion valves (E) separation column (F) flow scintillation detector and (G) control computer with automation software. Reproduced with permission from the Handbook of Radioactivity Analysis, Second Edition Chapter 14, page 1152. Copyright...

According to the location of the digestion unit in the system, there are two types of manifolds described in the literature to date before and after the injection unit. In the former arrangement, the sample is introduced into the microwave oven in a continuous flow [104] or stopped flow mode [105] after decomposition, the injected sample flows to the microwave oven unit together with the reagent(s) to be decomposed, and is then cooled and degassed prior to its delivery to the detector... 

Paschal DC, Ting BG, Morrow JC et al (1998) Trace metals in urine of United States residents reference range concentrations. Environ Res 76(l) 53-59 Poon R, Chu I (2000) Effects of trivalent antimony on human erythrocyte glutathione-S-transferases. J Biochem Mol Toxicol 14(3) 169-176 Poon R, Chu I, Lecavalier P et al (1998) Effects of antimony on rats following 90-day exposure via drinking water. Food Chem Toxicol 36(l) 21-35 Rahman L, Corns WT, Bryce DW et al (2000) Determination of mercury, selenium, bismuth, arsenic and antimony in human hair by microwave digestion atomic fluorescence spectrometry. Talanta 52(5) 833-843... 

Acid digestion is performed using a small volume (5 to 10 mL) of nitric acid alone or in conjunction with one of the previously mentioned acids on a hot plate. Alternatively, a laboratory-grade microwave unit, specifically designed for hot acid digestion, can be used. When the sample is boiled with acid, the latter should not be allowed to dry. The acid extract after boiling and cooling is diluted with water to a measured final volume for analysis. 

In general, organic extraction and acid digestion use different types of microwave apparatus, as these two processes require different reagents and different experimental conditions. A new commercial system, Mars X (CEM Corp., Matthews, NC) offers a duel unit that can perform both proce-... 

As stated in Section 5.3, there are two main types of microwave units, namely closed-vessel systems, which use pressurized containers, and open-vessel systems, which use focused microwaves at atmospheric pressure. Both types of system have been used to digest solid samples and each has its own advantages and disadvantages, so it is impossible to recommend either as the more suitable overall. 

United States Environmental Protection Agency, Microwave assisted acid digestion of sediments, sludges, soils and oils , EPA Method 3051, National Technical Information Service, Springfield, VA, 1994. 

Approximately 1 g of sample is weired into the digestion vessel, and 10 mL of nitric acid are added. The microwave unit is set to 30 W to cause a gentle reflux of the nitric acid. After about one hour or when the sample is nearly decomposed, the drop-wise addition of perchloric acid will typically complete the digestion. Perchloric acid is an extremely strong oxidizer that may react violently with organic material. Experienced personnel only should use it with utmost caution. The sample is heated until about 5 mL of solution remain in the vessel. The contents are washed into a 50-mL volumetric flask and brou t up to volume with water. 

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