Sample dissolution digestion

More recently, microwave ovens have been used for sample dissolution. The sample is sealed in a Teflon bottle or a specially designed microwave digestion vessel with a mixture of suitable acids. The high-frequency microwave, temperature (ca. 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 [25, 26],... 

Sample Dissolution — Sample introduction into most ICP systems, is by liquid nebuli-zation. This constraint partially limits the quality of the emission analysis to be dependent on the digestion, in the case of solid samples. The fact that several elements are easily monitored simultaneously places a greater demand on the care and choice of sample preparation. Also there are both advantages and disadvantages to the use of dissolved samples in analysis. Some disadvantages are ... 

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. 

A common result of the sample preparation is the dissolution of the entire sample, producing a clear solution. The digestion method must be selected to suit the type of sample, the metals being determined, and finally, the analytical method. Of the methods listed above, most require a liquid sample, except for x-ray fluorescence, which often is used on solid samples. Wet digestion in acid solution, dry ashing, and extraction of the analytes from... 

Table 5.1. Reagents Commonly Used in Sample Dissolution or Digestion...

Mineral samples such as rock, soil, and sediments require more aggressive digestion. Total sample dissolution may be done by several methods, and... 

The use of ICP-MS for trace analysis in sediments has recently been reviewed [326]. The advantages and disadvantages of acid digestion versus fusion-based sample dissolution were discussed. The problems involved in ICP-MS analysis of... 

The results confirmed that the ancillary materials used in an analytical procedures might contribute to blank values more than reagents themselves do, especially glassware and microwave digestion systems. Although the latter have been extensively employed to shorten the time required for sample dissolution, some problems have been ascribed to this procedure, as reported by Lima et al. [8],... 

Samples, as taken, are often unsuitable for direct analytical measurement. These samples will require some pre-treatment. Sample pre-treatment is a term used to encompass a variety of sample preparation procedures, including pre-concentration, clean up, extraction, dissolution, digestion and homogenisation. 

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. 

Decomposition involves the liberation of the analyte (metal) of interest from an interfering matrix by using a reagent (mineral/oxidizing acids or fusion flux) and/or heat. The utilization of reagents (acids) and external heat sources can in itself cause problems. In elemental analysis, these problems are particularly focused on the risk of contamination and loss of analytes. It should be borne in mind that complete digestion may not always be required as atomic spectroscopy frequently uses a hot source, e.g. flame or inductively coupled plasma, which provides a secondary method of sample destruction. Therefore, methods that allow sample dissolution may equally be as useful. 

Fe Multi-vitamin tablets UV irradiation for sample dissolution and thermal digestion using a 100 W tungsten lamp, HC1 and h2o2 UV-Vis 100—500 pg per tablet (1 g) Multi-commuted flow system in-line SPE for analyte separation/ concentration as chlorocomplex analogous flow system for the determination of Cu and Zn by FAAS [426]... 

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