Microwave assisted digestion

Finally, other salient uses of microwaves for treating solid samples such as microwave-assisted drying, distillation and protein hydrolysis are also briefly described. 

Sample digestion methods must efficiently decompose the sample matrix so that the target analytes can be thoroughly released from it and solubilized in a form compatible with the determination method of choice. 

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. 

The usual aim of digesting biological samples is the subsequent determination of metal traces potentially acting as nutrients or toxins, or even causing diseases such 

Biological (zoological, botanical, food) samples are primarily composed of three basic constituents, namely carbohydrates, proteins and lipids. Carbohydrates are the first constituents to decompose, at approximately 140°C, followed by proteins at ca. 150°C and lipids at about 160°C [14,150]. At each of these temperatures, significant increases in pressure are generated in the vessel with virtually no increase in temperature. Thus, for safety reasons and for determining the most efficient decomposition temperature, the analyst should have some knowledge of the constituents of the sample matrix. 

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In view of insufficient safety precautions for chemical operations, these systems are generally not recommended for microwave-assisted digestions of polymeric material. 

J. Gomez-Ariza, M.-A. Caro-de-la-Torre, I. Giraldez and E. Morales, Speciation analysis of selenium compounds in yeasts using pressurized liquid extraction and liquid chromatography-microwave-assisted digestion-hydride generation-atomic fluorescence spectrometry. Anal. Chim. Acta, 524(1-2), 2004, 305-314. 

P. Navarro, J. Raposo, G. Arana and N. Etxebarria, Optimisation of microwave assisted digestion of sediments and determination of Sn and Hg, Anal. Chim. Acta, 566(1), 2006, 37M4. 

Sturgeon et al. [343] have demonstrated that a continuous flow microwave-assisted digestion of soil samples gave an average of 90% recovery of trace elements with good precision. 

Microwave-assisted digestion procedures are used for total metal analysis in aqueous samples (EPA Method 3015) and for solid or oily samples (EPA Method 3051). These procedures allow for a rapid sample digestion with nitric acid under high pressure and temperature conditions the addition of hydrochloric acid is optional. Samples... 

Microwave-Assisted Digestion Procedures for Water Samples... 

Niemela, M., H. Kola, P. Peramaki, J. Piispanen, and J. Poikolainen. 2005. Comparison of microwave-assisted digestion methods and selection of internal standards for the determination of Rh, Pd and Pt in dust samples by ICP-MS. Microchim. Acta 150 211-217. 

Boch, K., M. Schuster, G. Risse, and M. Schwarzer. 2002. Microwave-assisted digestion procedure for the determination of palladium in road dust. Anal. Chim. Acta 459 257-265. 

It should be noted that microwave-assisted extraction (MAE) discussed in this chapter is different from microwave-assisted acid digestion. The former uses organic solvents to extract organic compounds from solids, while the latter uses acids to dissolve the sample for elemental analysis with the organic contents being destroyed. Microwave-assisted digestion of metals is covered in Chapter 5. 

This laboratory experiment describes the preparation of a vegetation sample (e.g., grass) for radiochemical analysis. The sample is dried and ashed. In Part 12A, the ash is fused with sodium hydroxide and sodium carbonate to bring it into solution. An alternative method in Part 12B uses a microwave-assisted digestion technique with nitric and hydrofluoric acid. The prepared sample is suitable for radionuclide analysis, notably for radio-strontium or plutonium. 

Step 4a. For microwave-assisted, digestion, follow the procedure developed for the microwave system in the laboratory. Note that total dissolution of the solid is required for radioanalytical chemistry, whereas partial dissolution is acceptable for other analytical processes if the method has been tested for fractional recovery. Several references are given below that may be helpful in developing or using this method. 

C. Lima, F. Barbosa, J. Krug, Comparison of ultrasound-assisted extraction, slurry sampling and microwave-assisted digestion for cadmium, copper and lead, J. Anal. Atom Spectrom., 15 (2000), 995-1000. 

C. Gerbersmann, M. Heisterkamp, F. C. Adams, J. A. C. Broekaert, Two methods for the speciation analysis of mercury in t>sh involving microwave-assisted digestion and gas chromatography-atomic emission spectrometry, Anal. Chim. Acta, 350 (1997), 273 D285. 

G. C. L. Araujo, M. H. Gonzalez, A. G. Ferreira, A. R. A. Noggueira, J. A. Nobrega, Effect of acid concentration on closed-vessel microwave-assisted digestion of plant materials, Spectrochim. Acta, 57B (2002), 2121-2132. 

M. A. Z. Arruda, M. Gallego, M. Valcarcel, Semi-on-line microwave assisted digestion of shellfish tissue for the determination of selenium by electrothermal atomic absorption spectrometry, J. Anal. Atom. Spectrom., 11 (1996), 169-173. 

Trace and ultratrace impurities (Ti, Zn, Ga, Nb, Sn, Sb, Te, several lanthanides, Ta, Ir, Pt, Pb, Bi and U) in the xgg range and below in wet digested steel samples (with aqua regia in a microwave oven) have been determined by ICP-ToFMS. For Ca determination in steel, an analytical procedure was introduced with microwave assisted digestion and matrix separation by flow injection ICP-MS to solve the interference problem ( C 02 and Si °0 on analyte ion " " Ca+) after treatment with H2SO4 and HF, and a detection limit of 0.6(xgg was obtained. The determination of trace and ultratrace impurities in high purity (4N) copper samples, after digestion... 

The capsule concept was reviewed in detail by Legere and Salin [90, 91]. The sample is handled in an encapsulated form until it is in the digestion solvent. Operation of the capsule-based microwave-assisted digestion system proceeds in several steps, during which temperature and pressure are monitored. 

Chakraborty, R., Das, A.K., Cervera, M.L., de la Guardia, M. Literature study of microwave-assisted digestion using electrothermal atomic absorption spectrometry. Fresenius 1. Anal. Chem. 355, 99-111 (1996)... 

Burguera, M., Burguera, J., Alarcon, O.M. Determination of zinc and cadmium in small amounts of biological tissues by microwave-assisted digestion and flow injection atomic absorption spectrometry. Anal. Chim. Acta 214, 421 27 (1988)... 

Sturgeon, R.E., Willie, S.N., Methven, B.A., Lam, W.H., Matusiewicz, H. Continuous-flow microwave-assisted digestion of environmental samples using atomic spectrometric detection. J. Anal. At. Spectrom. 10, 981-986 (1995)... 

CarriUio, E.N.V.M., Nogueira, A.R.A., Nobrega, J.A., de Souza, G.B., Cruz, G.M. An attempt to correlate fat and protein content of biological samples with residual carbon after microwave-assisted digestion. Eresenius J. Anal. Chem. 371, 536—540 (2001)... 

Matusiewicz, H. Critical evaluation of the effectiveness of nitric acid oxidizing systems pressurized microwave-assisted digestion procedures. Chem. Anal. (Warsaw) 46, 897-905 (2001)... 

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