Rectifying system-specific errors in NMR relaxation measurements

15N spin relaxation parameters provide a powerful tool for probing the internal dynamics and thermodynamics of proteins. The biological insight provided by these experiments often involves interpretation of small changes in relaxation parameters. This, in turn, requires careful data analysis, especially in the identification and treatment of systematic error. While progress continues on reduction of experiment-specific errors associated with pulse sequences, system-specific sources of error have received far less attention. The impact of these errors varies between facilities, spectrometers, and biological samples. We demonstrate that performing a series of control experiments along with relaxation measurements can help identify, quantify, and isolate sources of system-specific error, and, in some cases, correct for systematic changes. We further demonstrate that control experiments can be performed without significant loss of spectrometer time, and lead to more accurate relaxation parameter values.