Dissolution and digestion

The automation of preliminary operations involving a solid sample or a liquid sample containing a suspended solid Is far from easy, so much so that the elimination of human intervention In this tedious stage Is, understandably, of great interest. The best alternative to the automation of solid sample treatment is the use of robots mimicking the operations carried out manually by an operator (see Chapter 9). 

Systems requiring only partial dissolution of the sample call for llxlvia-tlon rather than dissolution or digestion. Such systems are dealt with in Section 4.9, devoted to solid-liquid extraction. 

Different configurations described in this chapter illustrating the relationships established in Fig. 4.1 

Technlcon s SOLIDprep II module, described in Chapter 3, is a representative example of automatic sample dissolution systems where up to 20 samples held on a turntable can be treated sequentially. An aliquot of the resultant 

Similar to the SOLIDprep Is the automatic system developed by Jackson at al. [1] for the determination of metal traces In foodstuff. As can be seen from Fig. 4.2, it consists of the following operational units  

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Pressure dissolution and digestion bombs have been used to dissolve samples for which wet digestion is unsuitable. In this technique the sample is placed in a pressure dissolution vessel with a suitable mixture of acids and the combination of temperature and pressure effects dissolution of the sample. This technique is particularly useful for the analysis of volatile elements which may be lost in an open digestion [24]. 

Speed. For applications where a great number of analyses must be performed on a routine basis, speed is perhaps the most important criterion for a system. Analytical procedures which often take more time than the actual analysis itself include such sample pretreatment procedures as dissolution and digestion. If these pretreatment steps could be kept to a minimum, analysis time would be cut down considerably. Also, mimimum pretreatment reduces the chances of sample contamination by the reagents used, or the loss of volatile elements during pretreatment. Thus the ideal system would require no sample pretreatment at all real systems should strive for minimum sample pretreatment. 

V. Cerda, J.M. Estela, On-line sample pretreatment dissolution and digestion. Ch. 6, p. 129, in S.D. Kolev, I.D. McKelvie (Eds.), Advances in Flow Injection Analysis and Related Techniques, Wilson and Wilson s Comprehensive Analytical Chemistry, vol. 54, Elsevier, Amsterdam, 2008. 

The materials comprising polar molecules, and especially liquids, absorb microwave radiation. Therefore, they can be heated easily in the ovens and hence are employed in reaction acceleration for dissolution and digestion of samples. 

Occlusions are minimized by maintaining the precipitate in equilibrium with its supernatant solution for an extended time. This process is called digestion and may be carried out at room temperature or at an elevated temperature. During digestion, the dynamic nature of the solubility-precipitation equilibrium, in which the precipitate dissolves and re-forms, ensures that occluded material is eventually exposed to the supernatant solution. Since the rate of dissolution and reprecipitation are slow, the chance of forming new occlusions is minimal. 

ABSTRACT The results of a soil geochemical survey of the Canadian Maritime provinces and the northeast states of the United States are described. The data presented are for the <2-mm fraction of the surface layer (0-5 cm depth) and C horizons of the soil. Elemental determinations were made by ICP-MS following two digestions, aqua regia (partial dissolution) and a strong 4-acid mixture (near-total dissolution). The preliminary results show that Hg and Pb exhibit elevated abundances in the surface layer, while As and Ni exhibit abundances that can be attributed to the geological provenance of the soil parent materials. 

Another method of bomb dissolution involves placing the sample and digestion mixture in a sealed PTFE bomb and then encasing this in a stainless-steel jacket. This may then be placed in a conventional oven for a period of several hours. This technique, although cheaper, takes substantially longer. 

Dissolution and Reduction. The cake obtained by digestion is dissolved in cold water or in dilute acid recycled from the process. A low temperature must be maintained (< 85 °C) to avoid premature hydrolysis, especially with the product from ilmenite. Air is blown in to agitate the mixture during dissolution. With the ilmenite product, the Ti02 concentration of the solution is 8-12 wt%, and with the slag product between 13 and 18 wt%. 

For the sample digestion of sediments, Scancar et al. found that significantly lower results were obtained for chromium, nickel and cadmium when aqua regia digestion was employed, compared to total acid dissolution and acetic acid extraction methods [266]. 

Solubilization of lipid digestion products in intestinal mixed micelles enhances their dissolution and dramatically increases the GI lumen-enterocyte concentration gradient that drives absorption by means of passive diffusion. Micelles, however, are not absorbed intact [8, 9], and lipids are thought to be absorbed from a monomolecular intermicellar phase in equilibrium with the intestinal micellar phase [10], The dissociation of monomolecular lipid from the micellar phase appears to be stimulated by the presence of an acidic microclimate associated with the enterocyte surface [11,12], In addition to passive diffusion, growing evidence suggests that active uptake processes mediated by transport systems located in the enterocyte membrane are also involved in the absorption of (in particular) fatty acids into the enterocyte [4],... 

A 2 mL aliquot of 25% TMAF1 was added [17] to samples with MW heating to achieve dissolution. The digestion mixtures were pretreated for 30 min in an ultrasonic bath. The digestion temperature was varied between 60 and 200°C Samples were weighed into glass digester [18]... 

Dissolution and Extraction in General For the dissolution of fish tissues different procedures are reported. Acid or alkaline digestion or solvent extraction is usually used for the separation of Hg species from biological matrices [45, 46]. For the quantitative extraction of Hg, four methods were examined HC1 leaching, alkaline-methanol extraction with tetramethylammonium hydroxide (TMAH) and... 

The sample is brought into solution by wet digestion or dry ashing—acid dissolution, and vanadium is determined by FAAS using a nitrous oxide-acetylene flame, or by EAAS. 

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