Newborn screening of phenylketonuria using direct analysis in real time (DART) mass spectrometry

Phenylketonuria (PKU) is commonly included in the newborn screening panel of most countries, with various techniques being used for quantification of l-phenylalanine (Phe). To diagnose PKU as early as possible in newborn screening, a rapid and simple method of analysis was developed. Using direct analysis in real time (DART) ionization coupled with triple-quadrupole tandem mass spectrometry (TQ-MS/MS) and with use of a 12 DIP-it tip scanner autosampler in positive ion mode, we analyzed dried blood spot (DBS) samples from PKU newborns. The concentration of Phe was determined using multiple reaction monitoring mode with the nondeuterated internal standard N,N-dimethylphenylalanine. The results of the analysis of DBS samples from newborns indicated that the DART-TQ-MS/MS method is fast, accurate, and reproducible. The results prove that this assay as a newborn screen for PKU can be performed in 18 s per sample for the quantification of Phe in DBS samples. DART-TQ-MS/MS analysis of the Phe concentration in DBS samples allowed us to screen newborns for PKU. This innovative protocol is rapid and can be effectively applied on a routine basis to analyze a large number of samples in PKU newborn screening and PKU patient monitoring.