Microwave acid digestion method methods

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. 

Sample Preparation Using Microwave Acid Digestion Method... 

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. 

The correct choice of sample preparation and analysis will give excellent confidence in the reported results. Microwave acid digestion methods can be used to prepare almost all... 

While additive analysis of polyamides is usually carried out by dissolution in HFIP and hydrolysis in 6N HC1, polyphthalamides (PPAs) are quite insoluble in many solvents and very resistant to hydrolysis. The highly thermally stable PPAs can be adequately hydrolysed by means of high pressure microwave acid digestion (at 140-180 °C) in 10 mL Teflon vessels. This procedure allows simultaneous analysis of polymer composition and additives [643]. Also the polymer, oligomer and additive composition of polycarbonates can be examined after hydrolysis. However, it is necessary to optimise the reaction conditions in order to avoid degradation of bisphenol A. In the procedures for the analysis of dialkyltin stabilisers in PVC, described by Udris [644], in some instances the methods can be put on a quantitative basis, e.g. the GC determination of alcohols produced by hydrolysis of ester groups. 

Method for Microwave Acid Digesting of Polyurethane, Polyphenylene Sulphite, Polysulphone and HDPE. Sample preparation for analysis of polyurethane, polypropylene terephthalate, polyphenylene sulphite, polysulphone, HDPE, PVC, polyethers, cellulose acetate, and natural wools for metal content is as for nylon with an additional step involving charring the sample prior to digestion. 

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. 

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 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...

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. 

Microwave acid digestion of the tissue, blood, serum, etc., can be used to prepare samples for metal analysis. The ICP-OES method is useful for monitoring the distribution of platinum compounds in the body but the information alone is not sufficient to support rigorous pharmacokinetic studies required to fully understand the total functionality as a cancer killing drug. 

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