Sample digestion techniques bombs

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]. 

Analysis of major elements (except Si) and total phosphorus on bomb-digested samples was accomplished by inductively coupled plasma emission spectrometry (ICP, ARL model 34,000). Silicon was analyzed colorimetrically (14). Phosphorus in total digests was also determined colorimetrically by the method of Murphy and Riley (15), as modified by Erickson (16). To avoid interference from fluoride ion used in the digestion technique, sample volumes were restricted to <1.5 mL in the standard P analytical protocol. 

Digestion Techniques For nonvascularized or low-water-content tissues such as bone, cartilage, or hair, a mechanical technique may do little to disrupt cellular structure and extract analytes. Extreme measures such as digestion with strong acid (i.e., 12 N HC1) are routinely used for DNA or nucleic acids, which can tolerate the harsh conditions. Alternatively, certain enzymes can be used to digest tissue samples. Commercial devices are available which contain digestion bombs fabricated from material resistant to corrosive media. 

The benefit of sample preparation techniques using microwave acid digestion and bomb combustion is that the sample is totally enclosed during the decomposition. These methods remove matrix interference and generate aqueous solutions, which can be analysed using ICP-OES. Sub-trace concentrations can be detected when hyphenated attachments are used, e.g. ultrasonic nebuliser, hydride generation or continuous cold vapour method. These methods are essential where trace levels of toxic elements are present that need to be identified and quantified. 

Tissues. Lead has been quantified in a variety of tissues, including liver, kidney, brain, heart, lung, muscle, and testes. Techniques for measuring lead in tissues are similar to those used for blood and urine. When AAS, GFAAS, or ASV are used for analysis, the samples may be wet ashed, digested with acid, or bomb digested (Blakley and Archer 1982 Blakley et al. 1982 Ellen and Van Loon 1990 Exon et... 

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. 

The first step in analysing plastics for metals content in polymers by ICP-AES technique is that they must be prepared in solutions that are suitable for nebulization. There are four general methods applicable for sample preparation for metal analysis by ICP-AES and they are solvent dissolution of some plastics dry ashing using a muffle furnace acid digestion using a microwave oven and oxygen bomb combustion. 

Digestion of samples using high pressure oxygen bomb combustion is an excellent technique for sample preparation, particularly trace metal analysis. This technique can be applied to most plastics provided that small sample ( 0.25 g) of fine grain sizes of plastics are used. The solutions obtained are clean and easily analysed for metal content against standards prepared in the same solution added to bomb. 

The selectivity and sensitivity offered by atomic spectroscopy techniques can be used for direct and indirect determination of metals in a range of pharmaceutical preparations and compounds. Metals can be present in pharmaceutical preparations as a main ingredient, impurities, or as preservatives which can be prepared for analysis using non-destructive (direct or solvent dilution) or destructive methods (microwave acid digestion, bomb combustion, extraction, etc.) and the metal of interest measured against standards of the metal prepared in the same solvents as the sample. Methods associated with some pharmaceutical products are already described in the international pharmacopoeias and must be used in order to comply with regulations associated with these products, e.g titration techniques are carried out according to methods that are the same for all pharmaceutical products. 

From a safety perspective, it is critical that no more than 0.1 g of sample be used for this technique. The sample is weighed into the Teflon digestion vessel. Approximately 4 mL of nitric acid are added. The vessel is capped and placed into the microwave oven. Four vessels are simultaneously processed. The microwave is set at 125 W for 15 min. The oven then ramps up to 190 W for another 15 min. Care must be taken not to keep internal temperature and pressure within the capability of the vessels. Excessive heat and pressure will cause the digestion bombs to deform and potentially leak. After the cycle is finished, the vessels are placed into an ice bath for at least one hour to cool. The dissolved sample is washed into a 25-ml volumetric flask and brought to volume with water. 

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]. 

Flame and GFAAS techniques have adequate sensitivity for the determination of metals in polymer samples. In this technique up to 1 g of dry sample is digested in a microwave oven for a few minutes with 5 ml of aqua regia in a small polytetrafluoroethylene-lined bomb, and then the bomb washings are transferred to a 50 ml volumetric flask prior to analysis by flame AAS. Detection limits (mg/kg) achieved by this technique were 0.25 (cadmium, zinc) 0.5 (chromium, manganese) 1 (copper, nickel, iron) and 2.5 (lead). Application of this technique gave recoveries ranging between 85% (cadmium) and 101% (lead, nickel, iron) with an overall recovery of 95%. 

The acid digestion bomb is another powerful technique for solubilization of plastic samples, in which the digestive process is carried out in a sealed pressurized vessel called a digestion bomb and heated in a muffle furnace. The advantage of this approach is that the temperature of the process may reach well above the boiling point of the mixtures in the normal process, thus making possible the complete solubilization of some slow or incompletely dissolving components under open-vessel conditions. Volatilization of some of the analytes as well as sample contamination from airborne particulates can be also minimized. 

An improved procedure has been described for atmospheric-pressure combustion of samples from high-purity metals [74]. High-pressure digestion with nitric and hydrofluoric acids 75], [76] and combustion techniques have both been shown to be suitable for the decomposition of samples of silicate-containing materials and fuels. Combustion in this case is carried out either in a stream of oxygen [77] or, to provide a closed system, in an oxygen bomb [78]. Mercury can be satisfactorily determined after prior Wickbold ashing [79]. 

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]. 

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