Applikationer

Cinchocaine (dibucaine) is used in the form of ointments or injection solutions as a local anaesthetic. Its base is soluble in diethyl ether; its hydrochloride, on the other hand, is insoluble in diethyl ether but easily soluble in water. This Bulletin describes the determination of cinchocaine in ointments, creams and injection solutions by means of differential pulse polarography. An acetate buffer pH = 4.8 is used as the supporting electrolyte. The limit of quantitation and the linear working range of the method are given. The necessary sample preparation steps are also dealt with in this Bulletin.

The water content of ointments is determined according to Karl Fischer. Because of their high water and fat content, the samples are prediluted with a 1:1 mixture of chloroform and methanol.

Propylene glycol, also called propane-1,2-diol, is a humectant and applied in topical solutions to increase the solubility of the active pharmaceutical ingredient (API) or the ability to penetrate the skin. In this application, propylene glycol is determined in a placebo and two topical solutions containing diclofenac as the API. The separation is achieved on a Hamilton RCX-30-250/4.0 column with subsequent pulsed amperometric detection (PAD).

Sodium metabisulfite, also known as pyrosulfite, is used as a preservative and antioxidant in pharmaceutical products. Metabisulfite is not stable in aqueous solutions and quickly converts to sulfite. The peak in the chromatogram originates from the sulfite. This process is however calibrated using metabisulfite standard solutions, which is why the results are specified as sodium metabisulfite. This Application Note describes the determination of metabisulfite as sulfite in an ointment. It is dissolved in an aqueous solution containing formaldehyde to protect the sulfite against oxidation.

Determination of lidocaine in ointments by potentiometric titration with sodium tetraphenylborate using the NIO surfactant electrode.