Abstract: Objective To investigate the feasibility of the new method of combining freeze grinding with ultrasonic technique for the pretreatment of the nail for toxicological and pharmaceutical analysis and to compare the advantages and disadvantages of this method with other traditional methods. Methods Five pretreatment methods were examined. Scanning electron microscope （SEM） was used to observe the micro-structural changes of the nail. Results The microscopic structure of nail totally destroyed after alkali treatment. The hierarchy mode of the internal structure became obvious and tight after acid hydrolysis, which became indistinct after methanol infiltration. The structure of nail broke to pieces after ultrasonic technique. After freeze grinding combined ultrasonic technique, the particle structure kept original shape, and its size was one hundred times smaller than which after manual way. Conclusion The freeze grinding combined ultrasonic technique can improve the release efficiency, and ensure the stability of the toxicant or drug during the pretreatment process. It is appropriate for toxicological and pharmaceutical analysis in the nail.

Key words: forensic toxicology, nails, microscopy, electron, scanning, ultrasonic wave, freeze grinding