It depends. Recovery of material(s) from mother liquor is a process and the need for validation should be assessed as for any other process step [ICH Q7, Section 14.40]. Recovery of material from mother liquor in any process step that must be controlled within predetermined criteria to ensure the API meets its specification is, by definition, a critical process step and should be validated. For example, recovery of API from mother liquor would be considered a critical process step and should be validated [ICH Q7, Sections 12.11, 12.12, 14.41, 14.43, 20 – see Glossary for definitions of ‘critical’, ‘materials’, ‘mother liquor’, and ‘validation’].
