Mass imaging of ketamine in a single scalp hair by MALDI-FTMS

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) coupled with mass spectrometry imaging (MSI) is a rapidly emerging technology that produces distribution maps of small pharmaceutical molecules in situ in tissue sections. Segmental hair analysis provides useful information regarding the state and history of drug use. A preliminary MALDI-Fourier transform ion cyclotron resonance (FTICR)-MSI method was developed for direct identification and imaging of ketamine in hair samples. After decontamination, the scalp hair samples from ketamine users were scraped gently and were fixed onto a stainless steel MALDI plate using double-sided adhesive tape. A Bruker 9.4 T solariX FTICR mass spectrometer with continuous accumulation of selected ions function was used in the positive ion mode. Four single hairs from the same drug abuser were analyzed. Three of four single hairs demonstrated ketamine spatial distribution, while only traces of ketamine were identified in the other one. The platform could provide detection power of ketamine down to the 7.7 ng/mg level in hair. MALDI-FTICR-MSI demonstrated the drug distribution over the whole hair length with higher spatial resolution compared with the traditional LC-MS/MS method after scissor cutting. Greater caution is needed in the interpretation of a single hair result because of the considerable variations in the growth rate and sample collection.