Quantification of protein concentration by the Bradford method in the presence of pharmaceutical polymers
Journal article, 2011

We investigated how the Bradford assay for measurements of protein released from a drug formulation may be affected by a concomitant release of a pharmaceutical polymer used to formulate the protein delivery device. The main result is that polymer-caused perturbations of the Coomassie dye absorbance at the Bradford monitoring wavelength (595 nm) can be identified and corrected by recording absorption spectra in the region of 350–850 mm. The pharmaceutical polymers Carbopol and chitosan illustrate two potential types of perturbations in the Bradford assay, whereas the third polymer, hydroxypropylmethylcellulose (HPMC), acts as a nonperturbing control. Carbopol increases the apparent absorbance at 595 nm because the polymer aggregates at the low pH of the Bradford protocol, causing a turbidity contribution that can be corrected quantitatively at 595 nm by measuring the sample absorbance at 850 nm outside the dye absorption band. Chitosan is a cationic polymer under Bradford conditions and interacts directly with the anionic Coomassie dye and perturbs its absorption spectrum, including 595 nm. In this case, the Bradford method remains useful if the polymer concentration is known but should be used with caution in release studies where the polymer concentration may vary and needs to be measured independently.

Carbopol

Controlled release

Polymer

Coomassie blue

Bradford assay

Chitosan

HPMC

Protein determination

Author

Nils Carlsson

Chalmers, Chemical and Biological Engineering, Physical Chemistry

Annika Borde

SuMo Biomaterials

Chalmers, Chemical and Biological Engineering, Pharmaceutical Technology

Sebastian Wölfel

Chalmers, Chemical and Biological Engineering, Pharmaceutical Technology

Björn Åkerman

Chalmers, Chemical and Biological Engineering, Physical Chemistry

Anette Larsson

Chalmers, Chemical and Biological Engineering, Pharmaceutical Technology

SuMo Biomaterials

Analytical Biochemistry

0003-2697 (ISSN) 1096-0309 (eISSN)

Vol. 411 1 116-121

Subject Categories

Pharmaceutical Sciences

Analytical Chemistry

Roots

Basic sciences

Areas of Advance

Life Science Engineering (2010-2018)

Materials Science

DOI

10.1016/j.ab.2010.12.026

More information

Latest update

8/18/2020