Particle-size distribution (PSD) of pulverized hair: A quantitative approach of milling efficiency and its correlation with drug extraction efficiency

- Pulverized hair was evaluated for homogeneity and particle size distribution (PSD).
- Freezing had a positive effect on hair pulverization when applied prior to milling.
- Different types of hair presented similar PSD at the optimized milling condition.
- PSD was well correlated with hair ketamine recovery by our LC-MS/MS method.

Different types of hair were submitted to different milling procedures and their resulting powders were analyzed by scanning electron microscopy (SEM) and laser diffraction (LD). SEM results were qualitative whereas LD results were quantitative and accurately characterized the hair powders through their particle size distribution (PSD). Different types of hair were submitted to an optimized milling conditions and their PSD was quite similar. A good correlation was obtained between PSD results and ketamine concentration in a hair sample analyzed by LC-MS/MS. Hair samples were frozen in liquid nitrogen for 5 min and pulverized at 25 Hz for 10 min, resulting in 61% of particles <104 μm and 39% from 104 to 1000 μm. Doing so, a 359% increment on ketamine concentration was obtained for an authentic sample extracted after pulverization comparing with the same sample cut in 1 mm fragments. When milling time was extended to 25 min, >90% of particles were <60 μm and an additional increment of 52.4% in ketamine content was obtained. PSD is a key feature on analysis of pulverized hair as it can affect the method recovery and reproducibility. In addition, PSD is an important issue on sample retesting and quality control procedures.