Sealed vessel digestion

Figure 1.6 A commercial anal3ftical microwave digestion system for sealed vessel digestion of multiple samples. Courtesy of CEM Corporation, Matthews, NC (www.cem.com).

Closed vessel microwave digestion for bones, teeth, hair, and soil Specially designed closed pressurized Teflon vessels may be used for microwave digestion. Teflon is transparent to microwaves, which enhances the effect of the acids by raising the temperature and pressure within the vessel. In addition the closed vessels will retain any volatile components (e.g., Si) in solution. It must, however, be emphasized that any sealed vessels must only be heated if they have been designed for the purpose. Examples of applications include Kingston and Walter (1992), Baldwin et al. (1994), Sheppard et al. (1994), and Tamba et al. (1994). 

Digestion is conveniently carried out in a Teflon-lined bomb (a sealed vessel) heated in a microwave oven.11 The vessel in Figure 28-8 has a volume of 23 mL and digests up to 1 g of inorganic material in up to 15 mL of concentrated acid or digests 0.1 g of organic material,... 

Similar to the CEM equipment, Milestone offers the modular MicroSYNTH platform, which is based on the ETHOS digestion instrument [40]. The diversity of different rotor and vessel systems enables reactions from 3 to 500 mL under open and sealed vessel conditions in batch/parallel manner up to 50 bar of pressure. The START package offers simple laboratory glassware for reactions at atmospheric pressure under reflux conditions (Fig. 6). A protective... 

It would be faster using a microwave oven (consider the domestic micro-wave oven and a conventional electric or gas cooker), particularly if the digestion is carried out in sealed vessels (pressure and temperature effects). 

Microwave digestion Method of digesting an organic matrix to liberate metal content using acid at elevated temperatures (and pressures) based on microwave radiation. Can be carried out in either open or sealed vessels. 

Open systems use focussed microwaves, which are guided on to the sample. Since pressure is not required to achieve high temperatures, non-sealed vessels can be used, with the benefit of being able to digest large amount of sample using a large volume of acid as indicated in the ISO standard (ISO 11466). 

A second approach also using high pressure and temperature is that of microwave assisted extraction. The sample is heated with the extraction solvent in a sealed vessel by microwave energy, as was described for microwave digestion. The temperature can be raised to about 150°C with the already described advantages of high temperature and... 

The mode of sample pretreatment depends on the analytical method used. If a mineralization of the specimen is required, the high volatility of mercury must always be kept in mind. If necessary, acid digestion at elevated temperatures should only be performed in sealed vessels (e.g., Teflon-or quartz-lined pressure bombs) and never in open vials. A digestion of blood or tissues with hydrochloric acid at room temperature for 15 hr extracts all mercury species sufficiently from the matrix. The supernatant is, for example, suitable for the flow injection technique of cold vapor atomic absorption spectrometry (CV-AAS) [111]. Furthermore, this cold digestion does not destroy organomercury compounds. Therefore the supernatant is suitable for a speciation [110]. 

Aoid digestion (i) In open vessels with convection or microwave heating (ii) In sealed vessels to increase the reaction pressure... 

Reactions were performed in sealed thick-walled glass tubes or in Teflon acid-digestion vessels, in domestic microwave ovens [13]. Teflon vessels can be used at pressures up to 14 atm, at temperatures below 250 °C, and are resistant to most commonly used chemicals, although they deform at temperatures >250 °C. 

Fig. 14.8 Simplified schematic diagram of a high-pressure digestion vessel with an EDL. A. plug and seal, B. quartz pressure reaction vessel with a sample solution, C. EDL with an antenna, D. vessel jacket with a screw cap, E. airflow. Adapted from Ref. [44],...

Acid digestion with a mixture of nitric, perchloric and hydrofluoric acids in sealed Teflon vessels, as described by McLaren et al. [136]. 

All four dissolution procedures studied were found to be suitable for arsenic determinations in biological marine samples, but only one (potassium hydroxide fusion) yielded accurate results for antimony in marine sediments and only two (sodium hydroxide fusion or a nitricperchloric-hydrofluoric acid digestion in sealed Teflon vessels) were appropriate for determination of selenium in marine sediments. Thus, the development of a single procedure for the simultaneous determination of arsenic, antimony and selenium (and perhaps other hydride-forming elements) in marine materials by hydride generation inductively coupled plasma atomic emission spectrometry requires careful consideration not only of the oxidation-reduction chemistry of these elements and its influence on the hydride generation process but also of the chemistry of dissolution of these elements. 

More recently, microwave ovens have been used for sample dissolution. The sample is sealed in a Teflon bottle or a specially designed microwave digestion vessel with a mixture of suitable acids. The high-frequency microwave, temperature (ca. 100-250°C) and increased pressure have a role to play in the success of this technique. An added advantage is the significant reduction in sample dissolution time [25, 26],... 

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