The first step in developing an analytical method is to select the most appropriate analytical technique. This choice will depend primarily on the critical quality attributes of the sample which need to be assessed, but also on the attributes of the technique such as:
- The principle of analysis
- Error sources
- Limitations or assumptions applied during the analysis process
- Analysis speed and degree of automation
Understanding the measurement principles that underpin a technique helps this initial choice and supports effective method development.
Method development relies on identifying the parameters that influence an analytical method and systematically assessing the impact of each one on the validity of the results. The aim is to establish an operating space within which the method consistently delivers reliable results. Typical factors which are considered include:
- Instrument set-up and configuration
- Sampling of a material for analysis
- Sample preparation, including requirements such as dispersion control
- Measurement process definitions, such as the time of analysis.
Method validation follows method development and verifies that an analytical method is fit for its intended purpose. It involves testing the method against the criteria that define its success. These criteria might include:
- Limit of detection
- Limit of quantification
Periodic re-evaluation is the final step in ensuring that the analytical method is robust. This ensures that the method is continuously improved and remains optimized for the application.