Quantification of protein concentration by the Bradford method in the presence of pharmaceutical polymers
Artikel i vetenskaplig tidskrift, 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.


Controlled release


Coomassie blue

Bradford assay



Protein determination


Nils Carlsson

Chalmers, Kemi- och bioteknik, Fysikalisk kemi

Annika Borde

SuMo Biomaterials

Chalmers, Kemi- och bioteknik, Farmaceutisk teknologi

Sebastian Wölfel

Chalmers, Kemi- och bioteknik, Farmaceutisk teknologi

Björn Åkerman

Chalmers, Kemi- och bioteknik, Fysikalisk kemi

Anette Larsson

Chalmers, Kemi- och bioteknik, Farmaceutisk teknologi

SuMo Biomaterials

Analytical Biochemistry

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

Vol. 411 1 116-121


Farmaceutisk vetenskap

Analytisk kemi


Grundläggande vetenskaper


Livsvetenskaper och teknik (2010-2018)




Mer information

Senast uppdaterat