Nails can be used as an alternative to hair for examining past drug use. However, daily hand-and-nail care can eliminate the internal drugs. Therefore, we developed an evaluation method to examine the effects of the external environment on drug stability in nails using micro-segmental analysis. First, reference nails containing drugs were prepared by collecting fingernails from participants who had consumed hay-fever medicines continuously for 4 months. Next, the entire free edge of a reference nail was cut into halves at the centerline
one side was stored as an untreated block, and the other was treated with various hand/nail care products. Both nail blocks were washed and segmented at 0.5-mm intervals in the width direction. Each segment in the extraction solution was crushed with stainless-steel beads, sonicated, and soaked in the solution for 24 h. The analytes in extracts were quantified by LC-MS/MS, and the drug concentrations between the treated and untreated blocks were compared. The drug concentrations decreased slightly in nails treated with manicure and gel-nail products. The analytes in nails tended to be lower in water-rich products such as hand soap and hand cream than in oil-rich products such as nailcare oil and acetone-free remover. The developed method using micro-segmental analysis enabled the evaluation of the effects of various hand/nail care products on drug stability in a limited number of nails. This would also be useful for examining the effects of severe environments on drugs in nails collected from cases of unnatural death.