Sensitive and simultaneous quantification of zinc pyrithione and climbazole deposition from anti-dandruff shampoos onto human scalp

• Simultaneous measurement of zinc pyrithione (ZPT) and climbazole (CBZ) deposition onto human scalp.
• Derivatization of ZPT with DPS prior to the analysis of UHPLC–MS/MS.
• Sensitive quantification of ZPT and CBZ at deposition levels in the low ng/cm2 range.
• Comparison of ZPT deposition onto scalp between dual-active and single active shampoos.

A sensitive ultrahigh performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method has been developed and validated for simultaneous quantification of zinc pyrithione (ZPT) and climbazole (CBZ) deposited onto human scalp from anti-dandruff (AD) shampoos. Scrubbing with a buffer solution was used as the sampling method for the extraction of ZPT and CBZ from scalp. Derivatization of ZPT was carried out prior to UHPLC–MS/MS analysis. The identification of ZPT and CBZ was performed by examining ratios of selected multiple reaction monitoring (MRM) transitions in combination with UHPLC retention times. The limit of detection for ZPT and CBZ was established to be 1 and 2 ng/mL, respectively. This sensitivity enables the quantification of ZPT and CBZ at deposition levels in the low ng/cm2 range. The method was successfully applied for the analysis of scalp buffer scrub samples from an in vivo study. The levels of ZPT and CBZ deposited on the scalp at different time points after application of the AD shampoo were measured. The results revealed that dual-active AD shampoo delivered more ZPT onto the scalp in a single wash than single active shampoo did. The amount of ZPT and CBZ retained on the scalp after AD shampoo application declined over 72 h.