A particle-into-liquid-sampler (PILS) coupled to ion chromatography (IC) analysis was deployed on board the DOE-G1 aircraft during the 2000 Texas Air Quality Study to determine the ionic components of aerosol particles with aerodynamic size smaller than 2.5 µm (PM2.5). The sampling frequency was 3 minutes with a sample integration time of ~120 seconds. Six ions, namely, NH₄⁺, SO₄^2-, NO₃^-, Na⁺, K⁺, and Ca²⁺, were quantified with a limit of detection of ~0.1 µg m^-3. While NH₄⁺ and SO₄^2- (median and maximum concentrations of 1.6 and 5.0, and 1.8 and 9.4 µg m^-3, respectively) dominated the ionic components, NO₃^- was typically very low, less than 0.2 µg m^-3, with occasional excursions reaching nearly half that of SO₄^2-. Na⁺ was nearly always present but at low concentration levels, i.e., < 0.3 µg m^-3. Although K⁺ and Ca²⁺ were observed in only ~15% of the samples, K⁺ reached as high as 6 µg m^-3. NH₄⁺ to SO₄^2- molar ratios were typically greater than 2 and frequently exceeded 4, suggesting the presence of additional anions. The total ion mass concentration correlated strongly with the PM2.5 mass estimated from the size/number distributions of accumulation mode particles. The mass fraction of the ions varied between ~40% and ~90%. The mass difference between the PM2.5 and total ions showed a good correlation with black carbon. Since organic carbon and black carbon are typically strongly correlated, this observation suggests that organic compounds dominated this mass difference.