Noise and Artifacts Peculiar to 2D Spectra

In 2D NMR a source of noise that is not evident in ID NMR has to be considered. Instabilities in the spectrometer system can cause small unwanted fluctuations in the amplitude, phase, or frequency of a resonance line. Such random fluctuations during the evolution period q (hence, called tx noise) are of significance only at frequencies H2 where there is a signal. On Fourier transformation this noise appears in sections parallel to the Wj axis. 

It is difficult to disentangle fj noise from a baseline artifact that causes an underlying ridge in the w, dimension. This ridge is the analog of the DC offset and baseline roll found in a ID spectrum when the first few data points are distorted. This effect can be eliminated or at least minimized by ensuring that the FT algorithm treats the first data point correcdy and that the spin system is in a steady state when the first data are recorded. 

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