Signal-to-noise ratio improvement

In a similar study with ESI the influence of different buffers was studied [12]. In the presence of acetic acid (HAc) only in the MeOH/H20 mobile-phase, a mass spectrum resulted with ion adducts of Na and K appearing as the most abundant ones. However, minor peaks could also be observed in the mass spectrum resulting from ammonium adducts (Fig. 4.3.2(A)). The respective ions could be suppressed or enhanced by changing the nature of the buffer used in the mobile-phase. For example, when a potassium buffer was used, sodium and ammonium adducts were suppressed, and the spectrum became less complicated with primarily the potassium adduct ion being visible (Fig. 4.3.2(C)). In addition, the signal-to-noise ratio improved by about a factor of 1.5-2. Similarly, sodium or ammonium acetate buffers enhanced the sodium and ammonium adduct ions, meanwhile suppressing other adducts (Fig. 4.3.2(B) and (D), respectively). 

In a typical Doppler measurement only one of the two annihilation photons with on average half of the Doppler shift is observed. With second detector opposite to the first one and operated in coincidence with the first one the full Doppler shift is observed. The signal to noise ratio improves by a factor of-1000. The shell structure of tightly bound core electrons of atoms does not change much when the atoms form a solid. Doppler shifts from these electrons can be detected and permit the identification of specific elements next to the annihilation site [70]. 

The total noise is the sum of both. If noise is random, it increases under summation as the square root of the number of experiments averaged, while the signal increases linearly. The signal-to-noise ratio improves with the square root of the number of experiments n... 

For an FTIR spectrometer, all of the spectral elements are observed for time T. Thus, the time spent sampling the resolution Av is also equal to T. Since the signal-to-noise ratio improves as the square root of the observation time... 

With an improved design of the UV cell, the light yield is better and the signal-to-noise ratio improves. 

For the same acquisition time the signal-to-noise ratio improves in the following order ... 

While these standard deviations are probably overly optimistic estimates of the system accuracy there exist several means for further improvement of the system performance usage of more than four frames simultaneously, better utilization of the frame format, averaging of frames for Signal-to-Noise-Ratio-improvement, and above all, selection of better illumination devices. 

The improved throughput offered by the Fourier transform method increases the brightness of the image focused on the detector which in turn produces a higher signal-to-noise ratio. The signal-to-noise ratio improvement expressed by the Jacquinot advantage is proportional to ( ft / d) 30d can be on the order of 10 to 20. 

The all important signal-to-noise ratio problem associated with composite material inspection is illustrated in Figure 16. Good signal-to-noise ratio is required for good signal detection and hence accurate thickness measurement, and defect detection and analysis. A brief review of some new directions on signal-to-noise ratio improvement can be found... 

In XAS measurement, multiple spectra are generally collected to improve signal-to-noise ratios, from a minimum of two spectra for concentrated samples to many hours, for example, for dilute biological samples. As beam intensity increases, the signal-to-noise ratio improves and less measurement time is required. Since other elements in the sample can cause scattering of X-rays, filters are sometimes used to remove this scatter. 

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