Bomb combustion method

The Determination of Selenium. The most difficult trace element to determine in coal by wet chemical methods is selenium. Two alternative dissolution techniques can be used—H. L. Rooks combustion method (7) and the oxygen bomb combustion method (4). Also, two alternative analytical methods can be used—the hydride evolution method (5) and the graphite furnace method. 

In both methods it is possible to lose some of the chlorine during combustion unless necessary precautions are taken. Thoroughly mixing the coal sample with Eschka mixture and covering this carefully with additional Eschka mixture minimizes the loss of chlorine. In bomb combustion methods, the ammonium and sodium carbonate solutions in the bomb are used to absorb the chlorine as it is released in the combustion. The 10- and 15-minute waiting periods and the slow release of pressure on the bomb help to prevent the loss of chlorine as well. 

A modification of the oxygen bomb combustion method (ASTM D-2361) for the determination of chlorine consisted of acidifying a solution of the adsorbed combustion products and titrating the chlorine potentiometrically. A potentio-metric titration was also tried for the determination of chlorine by the oxygen flask method. Combustion products, including chlorine, were absorbed in sodium hydroxide (NaOH), and the chloride was measured using silver-silver chloride electrodes. Although there was no statistical difference in results obtained from potentiometric titration and the Eschka procedure, the latter was more precise. 

Sample Preparation Using Oxygen Bomb Combustion Method... 

Sample preparation using the bombing combustion method has an advantage over the microwave digestion method in that it does not require very strong multi-acidic solutions... 

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. 

Both centrifuged and uncentrifuged samples were analysed by the bomb combustion method described in Section 5.10, as a comparison with results by the slurry method. 

Results. The slurry method of analysis of wear oils can give reproducible results when compared with the bomb combustion method (Table 5.19). The random selected metals analysed for this sample were used to show that this method could be used as an alternative provided that the particle sizes of insoluble suspensions in the oil are suitably small. This method may be an alternative to sample preparation by tedious destructive methods. 

Analysis of Epoxy Adhesives for Ge and B Content Using Oxygen Bomb Combustion Method... 

Table 6.20 Results of analysis of epoxy adhesives using the oxygen bomb combustion method...

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 three most widely used methods for sulfur determination are (1) the Eschka method, (2) the bomb combustion method, and (3) the high-temperature combustion method, and all are based on the combustion of the sulfur-containing material to produce sulfate, which can be measured either gravimetrically or volumetrically. 

There is general agreement that static-bomb combustion calorimetry is inherently unsatisfactory to determine enthalpies of formation of organolead compounds2,3. Unfortunately, as shown in Table 6 only three substances have been studied by the rotating-bomb method. The experimentally measured enthalpies of formation of the remaining compounds in Table 6 were determined by reaction-solution calorimetry and all rely on AH/(PbPh4, c). 

As referred to in the previous chapter, in bomb combustion calorimetry the reaction proceeds inside a pressure vessel—the bomb—at constant volume, and in this case the derived quantity is Ac U°. In flame calorimetry the reaction occurs in a combustion chamber, which is in communication with the atmosphere, and the measurements lead to ACH°. The methods of combustion calorimetry will be described in the following paragraphs. 

Static-bomb combustion calorimetry is particularly suited to obtaining enthalpies of combustion and formation of solid and liquid compounds containing only the elements C, H, O, and N. The origins of the method can be traced back to the work of Berthelot in the late nineteenth century [18,19]. 

Alternatively, the bomb combustion dissolution procedure can be combined with the hydride evolution method previously described for arsenic, tin, and bismuth. After completion of the bomb combustion and absorption of gases into the 10 ml of water, the solids are filtered out and the filtrate collected into a 50 ml volumetric flask containg 20 ml of hydrochloric acid. This is a suitable stock solution for the hydride evolution method. 

The graphite furnace method can also be used as described in the bomb combustion procedure. Table V compares graphite furnace values with conventional flame AAS or NBS neutron activation analyses. 

The first method (ASTM D-2361) offers a choice of two procedures for combusting the coal sample. In the bomb combustion procedure, the oxygen bomb used is the same as, or very similar to, that used in determination of the calorific value (ASTM D-2015 ASTM D-3286). 

ASTM D-3684. Standard Test Method for Total Mercury in Coal by the Oxygen Bomb Combustion/Atomic Absorption Method. 

Oxygen Bomb Calorimetry and Combustion Methods, Tech, manual 130, Parr Instrument Co., Moline, IL. 

Accurate experimental enthalpies of formation of iV-suhstituted imidazoles were measured using static bomb combustion calorimetry, the vacuum suhlimation drop method, and the Knudsen-effusion method <1999PCA9336>. 

Methods DBBC = Databook MS = mass spectrometry RB = rotating-bomb combustion calorimetry RS = reaction-solution calorimetry SB = static-bomb combustion calorimetry. 

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. 

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. 

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