Detection of trace protein in Chinese Materia Medica injections by soaking PVDF membrane

The main aim of this article was to develop a sensitive method to detect trace protein in Chinese Materia Medica injections (CMMIs). PVDF membranes of 9 mm² were kept in sample of 10 ml, and the membranes were washed with methanol to remove the stained color from CMMI. Then, the membranes were dyed with 0.25% Coomassie Brilliant Blue solution for at least 30 sec. After the dyed membrane was washed with a mixed solution of methanol-water-acetic acid (4.5:4.5:1) to remove the background, the membrane absorbed protein would be stably dyed in blue. The color intensity of the membrane was related to the protein content of the sample. This method was able to detect protein (>; 450 ng/ml) in 10 ml sample with high sensitivity and free of interference. This method even detected trace protein in two CMMIs from market in the present study. Compared with the method of sulfosalicylic precipitation adopted by China Pharmacopoeia of 2010 edition, this method is more feasible, and the sensitivity of this method is about 100 times higher. The results suggested that the method was useful to control trace protein in CMMIs.