Does anyone had an abundant impurity at the size of ~40 kDa while purifying His tag protein from Sf9 culture media on a HisTrap-FF column?

This impurity was observed only in the elution fractions (500 mM imidazole). There were no traces of it in the washes (20mM and 50 mM imidazole). 

09 August 2016 10,004 1 View