1.1   This document is to be used as a guide to Process Analytical Technology (PAT) instrument sampling and covers both the sample from which PAT data is collected and the sample that is taken for reference analysis. The ASTM definition of a guide is a compendium of information or series of options that does not recommend a specific course of action. The intention of a guide is to increases the awareness of information and approaches in a given subject area. As such, this guide should serve as a collection of points to consider when determining a sample practice for PAT instruments. It is not intended to serve as a practice to be followed. As a first step, one should define the overall goal of the PAT measurement. Once defined, this guide describes various considerations as they relate to the specific requirements that must be met to achieve the overall PAT goal, including the attributes to be measured, impact of the scale of the process, and interfacing of the measurement system to manufacturing equipment (including sampling system reliability). Additionally, it discusses the estimation and validation of the effective sample size and the overall contribution to the measurement. Related aspects of data collection and data processing as well as the use of risk assessments to optimize sampling and to understand the impact of potential sampling errors are also covered. Furthermore, considerations for process control and aspects pertaining to sample withdrawal and retention are included. Lastly, continuous manufacturing processes differ from batch manufacturing due to the time dependency associated with continuous operations and special considerations are needed for sampling of such processes.