Simultaneous determination of 3-chlorotyrosine and 3-nitrotyrosine in human plasma by direct analysis in real time–tandem mass spectrometry

A novel method for the simultaneous determination of 3-nitrotyrosine (NT) and 3-chlorotyrosine (CT) in human plasma has been developed based on direct analysis in real time–tandem mass spectrometry (DART–MS/MS). Analysis was performed in the positive ionization mode using multiple reaction monitoring (MRM) of the ion transitions at m/z 216.2/170.1 for CT, m/z 227.2/181.1 for NT and m/z 230.2/184.2 for the internal standard, d(3)-NT. The assay was linear in the ranges 0.5–100 μg/mL for CT and 4–100 μg/mL for NT with corresponding limits of detection of 0.2 and 2 μg/mL. Intra- and inter-day precisions and accuracies were respectively <15% and ±15%. Matrix effects were also evaluated. The method is potentially useful for high throughput analysis although sensitivity needs to be improved before it can be applied in clinical research.