6-Monoacetylmorphine in keratinized matrices can be used to discriminate between heroin users and individuals exposed to other sources of morphine alkaloids. Frozen pulverization is effective in preventing 6-monoacetylmorphine hydrolysis. The main aim of this study was to develop an LC-MS/MS method for the determination of five opiates in human fingernails using a frozen pulverization preparation method and to investigate the correlation between the concentration of opiates in nail and hair samples from subjects whose urine specimens were positive for morphine. Borate buffer (500 μL; pH 9.2) was added to 20mg of pulverized fingernail, followed by ultrasonication and liquid-liquid extraction. Analytes were analyzed on an Allure PFP propyl column by gradient elution. The mass spectrometer was operated in the positive electrospray ionization mode and multiple reactions monitoring mode. A total of 12 of 18 fingernail samples contained detectable 6-monoacetylmorphine (mean=0.43 ng/mg, range=0.10-1.37 ng/mg), morphine (mean=1.74 ng/mg, range=0.58-3.16 ng/mg) and codeine (range from
