Time averaged scan, single

Fig. 21. Raman spectra showing improvement of signal-to-noise using multiple scans with computer time averaging over single scan. Lower traces single scan upper traces multiple scans (10 scans) and computer output, (a) i of CCU (b) Hg emission line and n of LiCh (c) n of Na02 with oxygen isotopic counterparts (89).

The delay time between successive scans in a 2D experiment is, of course, of major importance for the sensitivity that can be obtained per unit time. For the case of a one-dimensional experiment in which a single 90° pulse is applied to a spin system and time averaging is used, we saw in Section 3.11 that the optimum time A between consecutive pulses is 1.27T, or alternatively that the Ernst flip angle can be used with more rapid repetition. For most 2D experiments, A = 1.27Tj is also close to optimum for a 90° pulse. This repetition time... 

There are three main modes of operation for LC-NMR on-flow, peak collection, and stopped flow. On-flow LC-NMR involves acquisition of realtime NMR scans during the chromatographic run, but requires high sample concentration since only a small number of scans can be averaged for each NMR spectrum. Stopped-flow LC-NMR is normally used when a single peak of interest is to be analyzed. The peak of interest is selected either manually, by region of time, or by intensity threshold. In stopped-flow mode, the LC... 

A Perkin Elmer Paragon 100 FT-IR spectrometer equipped with an MKII Golden Gate Single Reflection ATR system with a diamond ATR top plate was used to determine the changes in the chemical functionalities. The samples were clamped on the stage and scanned 4 times at 4 cm spectral resolution. The measurements were repeated at three locations and the collected spectra were averaged. 

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