Baseline curvature

The program fits the intensity at these point values to a polynomial (up to 5th order) function and then subtracts the polynomial function from the whole dataset. This is repeated for each ID slice (row or column) of the 2D data matrix. More sophisticated methods calculate the baseline points automatically and use functions other than polynomials. For example, a program called FLATT (by Kurt Wiithrich) is very effective at removing horizontal or vertical streaks resulting from baseline curvature in rows or columns of the data matrix. Especially with NOESY and ROESY databaseline correction is essential to getting clean 2D displays and plots. 

Figure 3. MAS spectrum at I g = 1.01 kHz, shown on two different vertical scales. Spinning sidebands are labeled according to their corresponding centerbands. Centerbands are indicated by asterisks. Baseline curvature is due to probe background. The ratios of sideband to cenlerband intensities are greater for C70 lines than for Cjo lines, indicating that the rotation of C70 molecules is more anisotropic.

To summarize, the correction for asymmetry of the measuring platforms in Fig. 4.54 due to their thermal resistances and their heat capacities with Eq. (3) eliminates the main effect of the baseline curvature with temperature, as is shown in Fig. A.11.1. Further corrections include the mass differences of the pans and the thermal resistance between calorimeters and measuring platforms. 

It is preferable when measuring the glass transition of polymers by DSC to have the sample baseline outside the transition region as horizontal as possible. TMDSC removes almost all baseline curvature or... 

First-order phase correction has one insidious effect, baseline distortion. A frequency-dependent phase shift cannot make up for the data that were lost during d the baseline error is just the DFT of the missing data. However, provided d is small compared to A, this baseline curvature can easily be corrected during postprocessing of the spectrum. In 2D... 

Finally, when more than normal baseline curvature is observed, it is corrected by heating the cell to 750 K for 4 to 6 hours, as recommended in the instruction manual for the instrument. 

Foods such as butter and margarines exhibit very wide melting envelopes (Figure 9.15), which can give problems with baseline curvature and slope over such wide temperature ranges. 

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