Digestion open vessel

Minimal pretreatment such as pelletizing, briquetting, grinding Acid digestion/dissolution in open vessels (atmospheric pressure)... 

Open vessel digestion (HN03) for bones, teeth, hair, and soil This is a standard preparation for most organic samples. In the case of soils, nitric acid will not fully dissolve all of the sample, but this method is sufficient to examine the total available elements. 

Open vessel digestion (HF HC104) for ceramics, glass, rocks, and soil These acids should completely dissolve most materials. HF removes the silica (as volatile SiF4), which reduces the total dissolved solid content and therefore reduces interferences, and C104 produces perchlorates, which are soluble (but explosive if dried out). The use of hydrofluoric and perchloric acids therefore has considerable safety risks and requires specialized fume hoods, handling equipment, and safety equipment. The hydrofluoric and perchloric acids are removed by a later evaporation stage unless the analytical instmment and safety considerations have been specially adapted. 

Table 14.9 Element recovery for closed vessel microwave digestion versus open vessel hot plate digestion of EPA sludge sample (all values are pg g-1)... 

Two arguments can he put forward in favour of wet chemical decomposition methods in open vessels, firstly, price, and, secondly, sample throughput. A wet decomposition can, if necessary, be performed with a beaker and a heating plate, whereas apparatus for modem high performance decompositions can cost as much as 25 000. With respect to sample throughput, the automatic wet digestion device can be used for up to 1 SO samples per hour for some materials. Such throughput cannot be realized by any other method. Some special cases exist that necessitate decomposition in open vessels (for instance, when the sample needs to be treated with perchloric acid). 

Some of the key areas of application for focused open-vessel microwave digestion have been described by Grillo [53]. 

Solid samples are digested with suprapure sub-boiled HN03 to avoid contamination in an acid mixture using HF, HC1 or 4 (e.g., in an open vessel directly or in a closed vessel by microwave induced digestion). The sample digestion of difficult-to-dissolve sample material in closed vessels,... 

Two open-vessel wet digestion methods using mixtures of nitric and sulfuric acids and H2O2 were developed and optimised to determine metals in plants... 

Figure 28-11 High-pressure autoclave allows digestion up to 270°C without HjSO, in open vessels inside autoclave. [Adaped from B. Maichin. M. /ischka. and G. Knapp. "Pressurized Wei Digestion in Open Vessels" Anal. Bioanal. Chem. 2003, 376, 715.]...

Wet digestions can be carried out in open vessels or in closed systems. In open systems, increased consumption of reagents requires the use of especially pure reagents. Considerable progress in the purification of reagent chemicals has been made over the... 

Open vessel acid digestion, one of the oldest techniques, is undoubtedly the most common method of sample decomposition or dissolution of organic and inorganic sample material used in chemical laboratories. This very inexpensive technique is of inestimable value for routine analysis because it can easily be automated all the relevant parameters (time, temperature, introduction of decomposition reagents) lend themselves to straightforward control. 

Dynamic systems for high-pressure microwave treatment were developed much later than open-vessel systems. Operating under a high pressure reduces the flexibility afforded by working at atmospheric pressure. However, some recently developed devices allow microwave-assisted high-pressure digestion and extraction in a dynamic manner [33,34]. 

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. 

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