One of the unexpected and significant results of the Cassini mission was the discovery of heavy organic negative ions in Titan’s ionosphere by the CAPS Electron Spectrometer (ELS) (Coates et al, 2007, Waite et al., 2007). These are observed during every encounter when the instrument points in the ram direction at altitudes between 950 and 1400 km. The heaviest ions observed so far have masses up to 13,800 amu/q (Coates et al., 2009). This indicates that complex hydrocarbon and nitrile chemical processes take place in Titan’s upper atmosphere. Studying the effects of different controlling parameters on the densities of different negative ion mass groups helps constrain the chemical formation and destruction processes (Wellbrock et al., 2013). The highest masses were observed during the T16 flyby. In this paper we present CAPS-ELS negative ion observations during T16 and discuss possible reasons for the particularly high masses observed during this encounter, which may include polar and seasonal effects.