Fourier transform infrared spectroscopy for the analysis of neutralizer-carbomer and surfactant-carbomer interactions in aqueous, hydroalcoholic, and anhydrous gel formulations

Abstract

The objective of the present study is to evaluate the polymersurfactant and polymer-neutralizer interactions in topical aqueous, anhydrous, and hydroalcoholic gel formulations using Fourier transform infrared (FTIR) spectroscopy. The gels were prepared by dispersing Carbomer (Carbopol 980) in water and ethanol for aqueous and anhydrous systems, respectively. Glycerol and propylene glycol were also added to ensure that the compositions of gels closely resembled those used in typical topical gel formulations. Comparisons of the spectra of Carbopol dispersions in aqueous, anhydrous, and hydroalcoholic systems, performed for the first time, show Carbopol-neutralizer and Carbopol-surfactant interactions vary depending on the nature of the solvents used for gel formation. Analysis of the spectra of aqueous gel formulations indicates significant presence of ionized carboxyl groups only at higher pH (~8.0). Drying of the aqueous gels causes a shift in the carbonyl stretch band toward higher energy, suggesting changes in polymer-neutralizer interaction. Anhydrous gels exhibit 2 different carbonyl stretch bands: the one at ~1653 cm -1 is related to the carboxyl group that is hydrogen bonded and is akin to hydrous gels; the second one at ~1717 cm -1 is indicative of free carbonyl groups. The carbonyl bands of dried gels appear at different energy levels than the solvated gels. This shift resulting from solvent evaporation, reported for the first time, indicates changes in hydrogen bond characteristics. The results show that FTIR can be a good technique compared with other more time-consuming means of analysis for topical formulations.

IR and Raman Investigation of Some Poly(acrylic) Acid Gels in Aqueous and Neutralized State

“…In the gels some of the carboxyl groups interact with water forming open dimers or oligomers [12]. As the concentration of polymer decreases the evolution towards open dimers is favorite that explains the shift towards 1642 cm −1 [24].…”

Material, Immunological, and Practical Perspectives on Eye Drop Formulation

“…That said, they impact the final structure of the gel and therefore must also produce the desired characteristics in the gel 88a. Aqueous versus anhydrous (alcohol) gel formation provides different structures and properties of gel, and these structural changes can inhibit the ability of certain polymer structures to deliver drugs effectively 108,109. The radiation‐initiated cross‐linking of some gels has the added benefit of sterilizing the gel,43 however preformed gels pose a challenge for topical application.…”

“…BAK is a common preservative, but has also been found to interact with carbomers and influence their viscosity, to the detriment of the desired improvement in bioavailability 88a,130. Due to the interference of preservatives with gel structures63a,87,88,109 and also the potential side‐effects of common preservatives,100,130,131 the manufacture of eye drops (especially multi‐dose formulations and gels) must be performed under sterile conditions to prevent the entrapment of pathogens in the drops that could be later released in vivo. Many preservatives, although useful for maintaining sterility, interact with the polymers and influence the structure of the gel 88a,114.…”

The Potential of Raman Spectroscopy as a Process Analytical Technique During Formulations of Topical Gels and Emulsions

“…When Carbopol is dispersed in any solvent, two types of interactions are responsible for gel formation -ionization or acid-base interaction between carbopol and polar solar solvent, and hydrogen bonding between polymer and solvent (16). There is a competition between these two interactions.…”

“…2a), solvent soluble salt of carbopol polymer is formed. The salt formation is responsible for uncoiling into extended structure of the carbopol polymers (16). Due to the increased ionic interaction as a result of this salt formation, enhancement of the 925 cm −1 peak occurred whereas the peak at 880 cm −1 diminished.…”