Digestion fusion methods

Acid digestions have the advantage that they provide sample solutions with lower dissolved solids contents than fusion methods, and allow removal of silicon as the fluoride by volatilization, thus avoiding the risk of chemical interference from large amounts of silicon. Care is needed when hydrofluoric acid is used with perchloric acid, on both safety and analytical grounds. Hydrofluoric acid causes severe burns if it comes into contact with skin, and any point of... 

The chemical compositions of the ancient Egyptian Blue samples (reported in the following section) were determined by atomic absorption spectrophotometry using the hydrofluoric acid digestion method together with the lithium metaborate fusion method for the silica determination (9). Some 20-30 mg of powder drilled from the objects was used for these analyses. Additionally, the arsenic concentrations were determined by x-ray fluorescence spectrometry. The precision of the analytical data was 1-2% for the major elements (>10% concentration) and deteriorated to 5-20% for the trace elements (<0.1% concentrations). However, due to the inhomogeneity of the material, variations in elemental concentrations (i.e., major, minor, and trace) of 10-15% can be expected within a single object. 

Destructive methods the determination of the amount of a substance in a material usually leads to the destruction of the test sample. This is realised by pretreatment techniques such as acid digestion, fusion, extractions etc. to bring the test sample into a liquid or other simple form compatible with the final determination technique or instrument. Nearly all modern methods of measurements, e.g. spectrometry, require sample pretreatment procedures. 

Inorganic Samples. Wet digestion, fusion, and pressure dissolution are common methods for the dissolution of metals, slags, ores, minerals, rocks, cements, and other inorganic materials and products. If the final solutions contain more than about 0.5% of dissolved material, the standards should also contain the major constituents in order to match the viscosity and surface tension. 

Fusion methods As an alternative to total digestion using acids, a sample may be brought completely into solution by first fusing it with an alkaline carbonate or borate, and dissolving the alkaline residue. 

In the fusion methods, cesium iodide is often added to the fusion mixture as a nonwetting agent to prevent the molten flux from adhering to the walls of the vessel, as well as to prevent incomplete transfer of the bead to the acid solution. In wet digestion of coal and fly ash using the Parr bomb, boric acid is added after digestion and the sample is heated for a further time on a water bath allowing the removal of unburned carbon. 

Colson has described an alkali fusion method for the determination of down to 500 ppm of sulfur in polymers [13] (See Method 2.6 at the end of this chapter) in which the sulfate in the digest is determined by titration either with O.OIN sodium hydroxide or by photometric titration with 0.01 barium perchlorate. 

In a fire-assay method used at the smelters, a weighed quantity of concentrate is mixed with sodium cyanide in a clay or porcelain cmcible and heated in a muffle furnace at red heat for 20—25 min. The tin oxide is reduced to metal, which is cleaned and weighed. Preliminary digestion of the concentrate with hydrochloric and nitric acids to remove impurities normally precedes the sodium cyanide fusion. 

Detection.—Apart from naturally occurring ores of vanadium, vanadium steels, and ferrovanadium, the commonest compounds of vanadium are those which contain the element in the pentavalent state, viz. the pentoxide and the various vanadates. The analytical reactions usually employed are, therefore, those which apply to vanadates. Most vanadium ores can be prepared for the application of these reactions by digesting with mineral acids or by alkaline fusion with the addition of an oxidising agent. When the silica content is high, preliminary treatment with hydrofluoric acid is recommended. Vanadium steels and bronzes, and ferrovanadium, are decomposed by the methods used for other steels the drillings are, for instance, dissolved in sulphuric acid and any insoluble carbides then taken up in nitric acid, or they are filtered off and submitted to an alkaline fusion. Compounds of lower valency are readily converted into vanadates by oxidation with bromine water, sodium peroxide, or potassium permanganate. 

An older Be method, P CAM 121, discusses air, dust, ore, and swipe samples. More vigorous digestion procedures such as hydrofluoric nitric acid for filters or potassium fluoride sodium pyrosulfate fusion and nitric acid digestion for ores. A nitrous oxide/acetylene flame is suggested for this method rarely used (Table HI). 

Typically, these will be alloys, rocks, fertilisers, ceramics, etc. These materials are taken into solution using suitable aqueous/acid media, according to solubility hot water, dilute acid, acid mixtures, concentrated acids, prolonged acid digestion using hydrofluoric acid if necessary, alkali fusion (e.g. using lithium metaborate), Teflon bomb dissolution. Fusion and bomb methods are usually reserved for complex siliceous materials, traditionally reluctant to yield to solubilisation. 

Tuckerman and collaborators state that chloric acid is to be preferred to the more widely used sulphuric acid or sulphuric-nitric acid digestions or alkaline fusions recommended for the determination of arsenic in organic compounds. Excess chloric acid is easily removed by boiling to leave a perchloric acid solution of inorganic As(V). Rapid micro and semi-micro methods for the determination of arsenic based on chloric acid digestion are described. 

AI for certification [3] pretreatment methods were either wet digestion (using mixture of acids, including HF) or fusion, or irradiation with thermal neutrons. 

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