Effervescent granules carbon dioxide

As an excipient, potassium bicarbonate is generally used in formulations as a source of carbon dioxide in effervescent preparations, at concentrations of 25-50% w/w. It is of particular use in formulations where sodium bicarbonate is unsuitable, for example, when the presence of sodium ions in a formulation needs to be limited or is undesirable. Potassium bicarbonate is often formulated with citric acid or tartaric acid in effervescent tablets or granules on contact with water, carbon dioxide is released through chemical reaction, and the product disintegrates. On occasion, the presence of potassium bicarbonate alone may be sufficient in tablet formulations, as reaction with gastric acid can be sufficient to cause effervescence and product disintegration. 

Sodium bicarbonate is generally used in pharmaceutical formulations as a source of carbon dioxide in effervescent tablets and granules. It is also widely used to produce or maintain an alkaline pH in a preparation. 

According to the 4th edition of the European Pharmacopoeia, the effervescent forms are defined as those granules or tablets that are to be dissolved in water before administration to patients. Effervescent tablets or granules are uncoated and generally contain acidic substances and carbonate or bicarbonate which reacts rapidly to release carbon dioxide when dissolved in water. Disintegration of the tablets usually occurs within 2 min or even less, due to the evolution of carbon dioxide. 

Sodium bicarbonate is the major source of carbon dioxide in effervescent forms and is able to provide a yield of 52% of carbon dioxide. It is commerdally available in five grades according to particle size, from free-flowing uniform granule to fine powder, which are odorless and slightly alkaline in taste. When heated, the bicarbonate is converted into anhydrous sodium carbonate. This reaction is time and temperature dependent. Ninety percent of the conversion is achieved within 75 min at 93°C, but dehydration starts at 50°C, which must be considered as a critical temperature in processing (12). 

The determination of carbon dioxide in effervescent granules is made by direct absorption. Gravimetric determination is preferable in laboratories where a considerable number of estimations of carbon dioxide are made, since, although the assembling of the apparatus is time consuming, when once set up a considerable saving of time is possible over other methods of determination ... 

Hepburn designed a simple apparatus for the volumetric determination of carbon dioxide, in which the gas, completely evolved from solution under vacuum, is absorbed in baryta water and the residual baryta titrated to phenolphthalein with 0-lN oxalic acid. Standard hydrochloric acid was found to give high results compared with oxalic acid. The time required for absorption was twelve to twenty-four hours. This method has been adopted by the B,P.C. for Effervescent Granules. 

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