The determination of arsenic (75As) was studied using an ICP-MS equipped with collision cell technology (CCT). Different mixtures of gases (He and H2) were tested using HCl conditions and a He flow rate of 4 mL min(-1) was found to be suitable for the removal of the poly-atomic spectral interference [40Ar35Cl]+. Trueness of the optimised method has been evaluated in both standard and CCT modes on six certified reference materials in foodstuffs of animal origin and on three external proficiency testing schemes (FAPAS). The results obtained generally coincided with the certified values, except for CCT mode in some categories of samples (meat, mussels and milk powder), for which a positive bias on results was observed due to the formation of poly-atomic interferences within the collision cell. The main interferences were studied and their contributions estimated. [58Fe16O1H]+ and [74Ge1H]+ were the most significant interferences formed in the cell. Finally, different parameters (e.g. hexapole and quadrupole bias voltage, nebuliser gas flow) were optimised to try to attenuate these interferences.