Experiment for label-free quantification of contaminants in preparations of EXTL3ΔN from transgenic HEK cells. EXTL3ΔN-expressing HEK cells were not untreated (untransfected / Batch C), treated with a set of CRISPR control plasmids (CRISPR control / Batch A), or treated with a set of CRISPR plasmids targeting EXT1 (CRISPR EXT1 / Batch B). EXTL3ΔN was then purified by HisTrap and size exclusion before analysing by mass spectrometry.