Acids digestion, acid attack

Reclaim Rubber. The process of reclaiming mbber by chemical digestion has been in use since the late 1800s. Early processes involved the treatment of the mbber cord mix with acid. Acids attack cotton, rayon, and nylon. The acid treatment was used to remove the reinforcing components. 

High-temperature/low-pressure inorganic digestions are an area of application that has benefited from recent advances in vessel and sensor design. The inert properties of Teflon and its resistance to acid attack make it the material of choice for microwave pressure-vessel construction. Improved commercial systems offer additional safety precautions and improved facilities for pressure and/or temperature control. Also, the distribution of microwave radiation inside the oven cavity is fairly homogeneous. Low-pressure systems allow decomposition temperatures of about 180 °C. However, for many matrices, such temperatures are not sufficient to guarantee the complete ashing of thermoresistant sample components. 

In the area of a gastric or duodenal peptic ulcer, the mucosa has been attacked by digestive juices to such an extent as to expose the subjacent connective tissue layer (submucosa). This self-digestion occurs when the equilibrium between the corrosive hydrochloric acid and acid-neutralizing mucus, which forms a protective cover on the mucosal surface, is shifted in favor of hydrochloric acid. Mucosal damage can be promoted by Helicobacter pylori bacteria that colonize the gastric mucus. 

The programmable addition of reagents at any time during the digestion, which makes allowance for sequential acid attack. 

To summarize this section, use of acid vapor-phase digestion and attack of some organic and inorganic matrices is a convenient and useful method of sample preparation. Closed pressure systems are the technique of choice to avoid loss of elements by volatilization while still maintaining extremely low values for the blank (by application of isopiestic distillation of the reagents and technical grade acids). 

Always check the condition of the digestion vessel liners, and (specifically) the outer layers for acid attack and wear. 

BRE (1995) Digest 279. Sulfate and acid attack on concrete in the ground recommended procedure for soil analysis. BRE, Garston, Watford WD25 9XX. 

The procedure below uses the simple digestion with nitric acid described by Bonilla, but avoids trying to determine the digest directly. Concentrated nitric acid attacks graphite tubes quite badly and can lead to premature fracture. Digests are diluted to an equivalent concentration of 10% v/v nitric acid and analysed against standards in the same matrix. 

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