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Analysis of aspirin tablets

A Metrohm UK product story
Edited by the Processingtalk editorial team Apr 5, 2007

A review of the possible history of aspirin from Metrohm, and a suggested method for the titrimetric determination of sodium bicarbonate in aspirin tablets using the Metrohm Titrando

It is still not exactly clear how aspirin came to be.

Many give the title of "discoverer of aspirin" to Felix Hoffmann, a chemist at Bayer, whose father suffered from rheumatism.

According to legend, Hoffmann's father was taking salicylic acid, already mass-produced, widely used, and highly profitable by the end of the 1870s, to treat his rheumatic condition.

Unfortunately, the drug was terribly irritating to the stomach and was associated with other ill-effects: most notably, in addition to having an unpleasant, sometimes nauseating, taste, it was believed that salicylic acid disrupted digestion and had an enfeebling action on the heart.

Therefore, the dutiful son took on the task of developing a less toxic replacement.

However, acetylsalicylic acid (ASA)--the common chemical name of aspirin--may have already been produced by the French chemist Charles Frederic Gerhardt in 1853, although he called his compound acetosalicylic anhydride, which was not necessarily the same as ASA.

The compound was synthesised in a purer form by Johann Kraut in 1869.

Indeed, acetylsalicylic acid was already being manufactured by the Chemische Fabrik von Heyden Company in 1897, although without a brand name.

Therefore, it is difficult to determine whether Hoffmann truly developed a new chemical compound or even a novel method of producing a known one, which could then have been patented in Germany.

The aspirin, sodium bicarbonate and citric acid combination is used to relieve pain occurring together with heartburn, sour stomach, or acid indigestion.

The aspirin in this combination is the pain reliever.

Aspirin belongs to the group of medicines known as salicylates and to the group of medicines known as anti-inflammatory analgesics.

The sodium bicarbonate in this medicine is an antacid.

It neutralises stomach acid by combining with it to form a new substance that is not an acid.

Aspirin, sodium bicarbonate, and citric acid combination may also be used to lessen the chance of heart attack, stroke, or other problems that may occur when a blood vessel is blocked by blood clots.

The aspirin in this medicine helps prevent dangerous blood clots from forming.

However, this effect of aspirin may increase the chance of serious bleeding in some people.

This ratio is critical, and slight increases or decreases of one or more components can have catastrophic affects.

The analysis.

The aspirin level is typically determined using UV.

The sodium bicarbonate on the other hand is determined by a non aqueous titrimetric method using perchloric acid as the titrant and glacial acetic acid as the solvent.

The basic unit of a Metrohm Titrando system consists of a titrator with one measuring interface that can be expanded.

The Titrando system is entirely oriented towards quality management according to GLP, GMP and 21 CFR Part 11.

As the dosing elements play an absolutely crucial role in titration the Dosing Units have a data chip from which the Titrando automatically reads all the data that it needs to carry out the titration properly.

Using a 809 Titrando in conjunction with the unique 800 Dosino dosing system the titration of sodium bicarbonate can be carried out fully in accordance to the pharmaceutical standard CFR 21 Part 11.

All of this is controlled using the full color 840 Touch Control.

The titration takes place in a completely sealed vessel, where the glacial acetic acid is added accurately using a second Dosino and after the titration, the whole contents of the titrated solution is aspirated to waste using the second bidirectional port of the Dosino.

A solvent blank is performed and this is automatically stored by the Titrando and then used in the subsequent calculation of the sodium bicarbonate concentration.

The indicator electrode used is the unique Metrosensor Solvotrode, combined pH glass electrode with easy-to-clean diaphragm, which is designed specifically for such demanding titrations.

Whole tablets can also be analysed by smashing up the tablet in situ using an in built homogeniser.

This sample preparation could be automated with the 789 Robotic Sample Processor XL.

In this case the homogeniser is mounted on a Swing Head with Robotic Arm, which makes the processing of large series of samples in multi-row racks possible.

For further information please contact Metrohm UK.

Find out more about this article. Request a brochure, download technical specifications and request samples here.
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