Table II.

Advantages and Limitations of TOF Analyzers

Advantage	Importance	Disadvantage	Importance
Rapid—many hundred measurements/day possible	High	Lack of API specificitya	High
High size resolution (>10 channels/decade)	Moderate	Particle coincidence possible at high aerosol concentrations	Moderate
Well-characterized sampling system with aerosol dilution possible	Moderate	Count (number)-rather than mass-weighted APSDs	High
Continuous tracking of particles through measurement zone	High	Particle density bias	Moderate—mainly of concern with DPIs
		Particle shape bias	Moderate—mainly of concern with DPIs
		No simulation of inhalation	Low to moderate—needed to test spacers

API active pharmaceutical ingredient, APSD aerodynamic particle size distribution, DPI dry powder inhaler, TOF time of flight

^aWithout abbreviated impactor-inlet accessory