What is Theory of Sampling (TOS)? TOS is a theory about the sampling of materials. Here are some recommended links. Links Gy’s sampling theory TOS forum edited by Professor Kim H. Esbensen Presentations Representative Sampling – a critical success factor for all analytical endeavors (incl. NIR), Kim Esbensen, IDRC 2014 Papers Theory of sampling (TOS) versus measurement uncertainty (MU) – A call for integration, Kim H. Esbensen, Claas Wagner Books Process Analytical Technology: Spectroscopic Tools and Implementation Strategies for the Chemical and Pharmaceutical Industries, Second Edition, Chapter 3. Process Sampling: Theory of Sampling – the Missing Link in Process Analytical Technologies (PAT), Katherine A. Bakeev, Kim H. Esbensen and Peter Paasch-Mortensen Related: Why NIR Method Maintenance?