Application Note - Magnetic Resonance

Quantification of Oxyethylene in Poloxamers in Full Automation on the Fourier 80

Poloxamers are synthetic block copolymers composed of a central hydrophobic oxypropylene chain connecting two hydrophilic oxyethylene ends. An attractive variety of valuable applications in fields such as drug delivery and cosmetics have been found, taking advantage of their amphiphilic and surfactant properties. The quantification of the oxyethylene content is of great interest. A poloxamer’s ability to self-assemble and form a thermo-gel for instance is highly related to its composition. To quantify the oxyethylene weight percentage in poloxamers USP-NF (United States Pharmacopeia - National Formulary) suggests Nuclear Magnetic Resonance Spectroscopy. [1] This official quantification procedure described by the USP-NF was performed in an entirely automized fashion on the Fourier 80, Bruker’s FT-NMR benchtop spectrometer.

Multiple poloxamers differing in the amount of repetition units are commercially available under the trade names Kolliphor®, Pluronic® and Synperonic®. They are identified by a characteristic Poloxamer number “xyz”, where the digits xy multiplied by a factor of 100 corresponds to the approximate molecular mass of the oxypropylene center and z multiplied by 10 describes the oxyethylene content in percentage.1 1H 1D NMR spectra of poloxamers show two significant peak regions; one region at approximately 3.7 ppm, corresponding to the -CH2 and -CH groups and a doublet at around 1.1 ppm resulting from the oxypropylene methyl groups.

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