Microwave Acid Digestion Bomb

Decomposition in closed Teflon vessels at high pressure (up to 85 bar) with microwave heating. (Microwave Acid Digestion Bomb, Parr Instrument Company, USA.)... 

S.R. Grobler, A.J. Louw, A new microwave acid digestion bomb method for the determination of total fluorine. Caries Res. 32 (1998) 378-384. 

Nicholson, J.R.P., Savory, M.G., Savory, J., Wills, M.R. Micro-quantity tissue digestion for metal measurements by use of a microwave acid-digestion bomb. Clin. Chem. 35, 488 90 (1989)... 

Fish (total) Digestion of samples with nitric acid in a microwave acid digestion bomb, reduction to elemental mercury CVAAS 0.195 ng/mL >95 Navarro et al. 1992... 

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. 

Total decomposition of the sample, the purpose of which is to release fluorine from inorganic or organic matrixes and convert it to fluoride ions, is usually a prerequisite for determining the amount of total fluorine. Commonly used procedures involve oxygen bomb combustion in a closed bomb [176,180], open ashing [181,182], alkali hydroxide or alkali carbonate fusion [151,183-187], pyrohydroly-sis [187-191], acid extraction [192,193] and microwave acid digestion [194-196]. 

Table 4.10 Results of analysis of selected plastic materials for listed metals by ICP-AES after microwave acid digestion (A), dry eishing to 650°C with PTSA (B) or high pressure oxygen bomb combustion (C)...

Dry ashing of cmde oils can cause serious loss of ash or elements through volatility of some metals, even in the presence of metal-retaining compounds. The methods using microwave acid digestion or bomb combustion are suitable for sample preparation for most trace metal analysis because they are retained in solution. This includes those that are volatile. Unfortunately, these methods are time-consuming and can be erroneous, and require experience skilled operators, but are necessary because they are precise, accurate and quantitative. 

The concentration of metals that are detrimental to catalysts added can vary between 20.0 ppm for Fe to 100 ppm for Ni and lOOOppm for V. The presence of these metals necessitates the need for analysis of these metals to determine their concentrations prior to the cracking process. The best method to analyse these oil samples needs to be rapid and accurate. Careful selection of the method either from experience or by trial and error may be applied depending on the metal and the concentration. Sample dissolution in a solvent or solvent mixture is considered the easiest but may not be suitable for low limits of detection. Destructive sample preparation methods, i.e. oxygen bomb combustion, microwave acid digestion followed by pre-concentrating may be required for trace analysis and/or with the aid of a hyphenated system, e.g. ultrasonic nebuliser. Samples prepared by destmctive methods are dissolved in aqueous solutions that have very low matrix and spectral interferences. 

Results. The results obtained by this experiment were between 95 and 109% which is indicative of a good recovery for the listed elements using the ashing method. The metals Pb and Sn were included to test for their volatility in this type of sample (Table 5.13). The method works well for some metals but not for volatile metals. These samples can also be prepared using microwave acid digestion or bomb combustion methods. 

Comparative Study of Analysis of Trace Levels of Toxic Metals Using Microwave Acid Digestion and Oxygen Bomb Combustion... 

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. 

Table 5.18 Results of comparative study of analysis of 250 ggkg-1 of spiked toxic metals after sample preparation using microwave acid digestion and oxygen bomb combustion. Results in brackets are percentage recovery...

To monitor these concentrations of stabilisers for precise, accurate measurements a method must be available that must detect levels as low as 600 ngg-1 and as high as 5000 ngg-1. The allowed tolerance can vary between 20% for low levels to 10% for higher levels without affecting the performance of the product. The lower concentration would be expected to cure faster than those containing higher concentrations of stabiliser. The different level of stabiliser is dictated by the application of these adhesives and must be formulated under very controlled conditions. ICP-OES is an ideal tool to monitor the metal type stabilisers using sample dilution, bomb combustion or microwave acid digestion methods. 

Cyanoacrylate adhesives can be prepared for metal analysis using destructive techniques e.g. dry ashing, microwave acid digestion or oxygen bomb combustion. It is a matter of... 

Table 6.27 Results of analysis of polyurethane (PU) adhesives spiked with 0.1 % organometallic catalysts using destructive methods ashing, microwave acid digestion and bomb combustion methods of sample preparation...

Mercury salts that are present in the formulations in Table 7.8 are used in low and controlled concentrations and must be analysed for their concentration prior to use. Therefore, sample preparation is usually carried out in closed vessels such as microwave acid digestion or bomb combustion and diluted in deionised water to a known volume. 

MAD, microwave acid digestion BC, bomb combustion Chelex 100, chelator extraction by column or separating funnel. 

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