The mass spectra of positive ions generated in a positive high-voltage point-to-plane corona and negative ions generated in a negative high-voltage point-to-plane corona in high-purity SF₆ are reported. In the absence of added impurities the major positively- and negatively-charged ions are SF₅⁺, SF₃⁺, SF₂⁺, SF⁺, SF₆^-, SF₅^- and F^-. Evidence for the formation of SF₆ corona discharge neutral by-products, SF₄ and SF₂, is observed from the presence of cluster ions, SF_x⁺(SF₄) and SF_x⁺(SF₂), x=2, 3. Based on analyses of predicted ion intensities from cross-section data, SF₂⁺ and SF⁺ ions are attributed to SF₂ in the discharge, while most of the SF₃⁺ observed is attributed to SF₄. In the case of negative ions, analyses indicate that F^- is formed in the discharge at high-density normalized electric field, E/N, from both dissociative attachment of SF₆ and ion conversion processes, while SF₆^- and SF₅^- are likely to be formed outside the glow. Other ions observed resulting from the presence of trace contaminants include SOF₃⁺, SOF₂⁺, SOF⁺, SOF₅^- and F^-(HF)₂. In this paper (part I) the various sources of ions produced in 'pure' SF₆ corona are discussed while in part II the effects of water and SF₆ neutral corona by-products on ion formation are discussed.