Bromine combustion analysis

Principles and Characteristics Combustion analysis is used primarily to determine C, H, N, O, S, P, and halogens in a variety of organic and inorganic materials (gas, liquid or solid) at trace to per cent level, e.g. for the determination of organic-bound halogens in epoxy moulding resins, halogenated hydrocarbons, brominated resins, phosphorous in flame-retardant materials, etc. Sample quantities are dependent upon the concentration level of the analyte. A precise assay can usually be obtained with a few mg of material. Combustions are performed under controlled conditions, usually in the presence of catalysts. Oxidative combustions are most common. The element of interest is converted into a reaction product, which is then determined by techniques such as GC, IC, ion-selective electrode, titrime-try, or colorimetric measurement. Various combustion techniques are commonly used. 

Ion chromatography has been successfully applied to the quantitative analysis of ions in many diverse types of industrial and environmental samples. The technique has also been valuable for microelemental analysis, e.g. for the determination of sulphur, chlorine, bromine, phosphorus and iodine as heteroatoms in solid samples. Combustion in a Schoniger oxygen flask (Section 3.31 )is a widely used method of degrading such samples, the products of combustion being absorbed in solution as anionic or cationic forms, and the solution then directly injected into the ion chromatograph. 

Applications Basic methods for the determination of halogens in polymers are fusion with sodium carbonate (followed by determination of the sodium halide), oxygen flask combustion and XRF. Crompton [21] has reported fusion with sodium bicarbonate for the determination of traces of chlorine in PE (down to 5 ppm), fusion with sodium bisulfate for the analysis of titanium, iron and aluminium in low-pressure polyolefins (at 1 ppm level), and fusion with sodium peroxide for the complexometric determination using EDTA of traces of bromine in PS (down to 100ppm). Determination of halogens in plastics by ICP-MS can be achieved using a carbonate fusion procedure, but this will result in poor recoveries for a number of elements [88]. A sodium peroxide fusion-titration procedure is capable of determining total sulfur in polymers in amounts down to 500 ppm with an accuracy of 5% [89]. 

Volatility of the Elements and Sample Treatment. A prime consideration in developing an analysis method is the volatility of the element to be determined. Controlled combustion of the coal sample and collection of the volatile products is a good way to separate very volatile elements such as mercury and bromine. The few completely volatile elements are subsequently and easily purified. 

Analysis of Size-Fractionated Particles. A series of samples was analyzed by both methods of analysis, and the results of two samples that were collected on different days are shown in Tables III and IV. The data shown in Table III illustrate that there are probably two origins of the elements. Vanadium, bromine, manganese, copper, mercury, chromium, and zinc increase in concentration as the particle size decreases. This inverse relationship is expected if these particles are emitted by high-temperature combustion processes such as automobiles and power plants (which are the major sources in this area). Sodium, aluminum, iron, scandium, and cobalt were present in an approximately uniform distribution throughout the particle size range. This relationship results... 

Prins et al. (21) described the lower flammability of poly-bromostyrene relative to that of polystyrene. On the basis of thermal analysis experiments, they suggested that bromine inhibited most of the oxidative chain reactions, and thus the combustion was not supported (vapor-phase mechanism). Khanna and Pearce (16) and Brauman (22) demonstrated that polystyrene could be flame retarded by appropriately modifying its structure with substituents that promote the char yield of the system (condensed-phased mechanism). 

Further insight into the mode of action of inorganic synergists in halogen-containing polymer formulations has been provided by quantification and analysis of the char residues remaining after combustion of the polymer in air. Data for such experiments on brominated polyester resins are presented in Table 7. 

Bromine radicals released during thermal decomposition of BFRs act as efficient electron scavengers to inhibit combustion. Other flame retardants that utilize chlorination or phosphorylation to inhibit combustion have been developed however, current usage of these materials is insignificant compared with brominated reagents. Methodologies used for the analysis... 

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