Pressure Dissolution Technique

Two main methods have been used to digest polymer samples before the determination of metals (i) pressure dissolution in sealed Teflon lined steel bombs or (ii) dissolution in sealed bombs in a microwave oven. 

Once the sample is in solution in the acid and the digest made up to a standard volume, the determination of metals is completed by standard procedures such as AAS and ICP-OES. 

Microwave ovens have also been used for polymer dissolution. The sample is sealed in a Teflon bottle or a specially designed microwave digestion vessel with a mixture of suitable acids such as nitric acid, and aqua regia and, occasionally, hydrofluoric acid. Perchloric acid must not be used in these bombs due to the risk of explosion. The high-frequency microwave temperature ( 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 [67, 68]. 

Element (a) in HN03 H20 (1 1) (b) in HN03 H202(5 3) Certified value (%) 

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G.J. DeMenna and W.J. Edison, Novel Sample Preparation Techniques for Chemical Analysis - Microwave and Pressure, Dissolution, Chemical Analysis of Metals, ASTM STP 994 (F.T. Coyle, ed.), American Society for Testing and Materials, Philadelphia, PA (1987), p. 45. 

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]. 

Reverz, R. and Hasty, E. (1987) Recovery study using an elevated pressure temperature microwave dissolution technique. Paper presented at the Pittsberg Conference and Exposition on Analytical Chemistry and Applied Spectroscopy, March 1987. 

Two additional hydrofluoric acid methods have been reported (1,2), and are similar to that described above. The method of Hughes et al. has also been the subject of two comparative studies relevant to the analysis of ceramics (2,31). Techniques that retain silicon have been discussed (1,2) and involve either fusion with lithium metaborate [or sodium carbonate (2)] or high pressure dissolution in a PTFE bomb. An alternative high pressure method, developed by Price and Whiteside (32), was evaluated in the course of this investigation but was found to be unreliable for stained glass of medieval composition in many experiments dissolution was incomplete. Attempts to modify the procedure by varying the prescribed dissolution parameters produced insufficiently consistent results although superior conditions were established (Table I). 

High temperatures are required to melt the crystalline domains in the high-EW samples and promote dissolution. Martin et have recently found that Nafions with EWs of 1100 and 1200 dissolve in both 50 50 propanol-water and 50 50 ethanol-water, at 250°C and elevated pressure, because the crystallites of the materials are eliminated. McCain and Covitch have also reported a similar dissolution technique. The ionic membrane was chemically converted into the nonionic precursor (sulfonyl fluoride) form prior to the dissolution process. Due to the nonionic nature of the precursor, it dissolves under relatively mild conditions. These dissolution techniques for Nafion polymers provide an important means for preparation of chemically modified electrodes and membranes of any desired geometry. ... 

Pressure Dissolution. Pressure dissolution is essentially a wet digestion procedure which is carried out under pressure. Advantages of this technique are (i) The pressure dissolution is much faster than conventional wet digestion (ii) The procedure eliminates losses of volatile components e.g. Hg or SiF4) (iii) The decomposition of more difficult samples is possible. 

Alternatives to pressure dissolution of air have been tried during the development of the process technique. These methods of bubble generation include ... 

Electroflotation is not economical in the treatment of wastewater and generally pressure dissolution of air (dissolved air flotation) is the most widefy used method and it is this technique that is discussed in detail below. The objective of the process is to remove by flotation the flne-sized difficult to settle particles firom a su ision. In wastewater treatm t the suspmsion is usually dilute and the operation is clarification the method can also be readily used to thickm and concentrate snspenaons as in an activated sludge process. 

R. Reverz and E. Hasty, Recovery Study Using an Elevated Pressure Temperature Microwave Dissolution Technique, Pittsburgh Conference and Exposition of Analytical Chemistry and Applied Spectroscopy, 1987. 

For the purpose of the identification and quantification of additives (broadly defined) in polymeric materials extraction and dissolution methods are favoured (Sections 3.3-3.7). However, additives are also made accessible analytically by digestion of the sample matrix (cf. Section 8.2). Such wet chemical techniques, that remove the sample matrix first, are often limited to mg amounts because of pressure build-up in destruction vessels. Another reactive extraction approach to facilitate additive analysis is depolymerisation by acid hydrolysis or saponification, sometimes under pressure. This is then frequently followed by chemical methods such as titrimetry or photometry for final identification and quantification. 

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