Host cell proteins (HCPs) are bioprocess-related impurities arising from cell-death or secretion from non-human cells used for recombinant protein production. Clearance of HCPs through downstream purification (DSP) is required to produce safe and efficacious therapeutic proteins. While traditionally measured using anti-HCP ELISA, more in-depth approaches to HCP characterisation may ensure that risks to patients from HCPs are adequately assessed. Mass spectrometry methods are likely to provide rationale for targeted removal strategies through the provision of both qualitative and quantitative HCP information. A high pH low pH reversed phase data independent 2D-LC-MSE proteomic platform was applied to determine HCP repertoires in Protein A purified monoclonal antibody (mAb) samples as a function of culture harvest time, elution buffer used for DSP and also following inclusion of additional DSP steps. Five commercially available biotherapeutic mAb products were also analysed. Critical quality attributes (CQAs) were examined for mAbs purified with different Protein A elution buffers to ensure that the selected buffers not only minimised HCP profile but also had no adverse effect on product quality. Our results indicate that an arginine based Protein A elution buffer minimised the levels of HCPs identified and quantified in a purified mAb sample and also demonstrated no impact on product CQAs. It was also observed that mAbs harvested at later stages of cell culture contained higher concentrations of HCPs but that these were successfully removed by the addition of DSP steps complimentary to Protein A purification. Taken together, our results show how mass spectrometry based methods for HCP determination in conjunction with careful consideration of processing parameters such as harvest time, Protein A elution buffers and subsequent DSP steps can reduce the HCP repertoire of therapeutic mAbs.