Signal to noise enhancement

Practicable isotopic enrichment has the following prerequisites adequately short time for the enrichment process, acceptable asymptotic enrichment factor, and adequate accuracy for the estimation of the enrichment factor. (When total activity, rather than specific activity, is limiting, one must also pay attention to losses during enrichment.) For the argon and carbon enrichments referred to above, enrichment factors of about 100 and 500 were obtained within a week and a few hours, respectively and enrichment factors were deduced from direct observations of adjacent, stable isotopes. The 14C enrichment process provided extra dividends for AMS measurement the sample was implanted in an ideal form for the accelerator ion source, and it was spatially localized (depth) which gave added signal-to-noise enhancement. 

R. Siegel, T. T. Nakashima and R. E. Wasylishen, Signal-to-noise enhancement of NMR spectra of solids using multiple-pulse spin-echo experiments. Concepts Magn. Reson., 2005, 26A, 62-77. 

Enke, C.G. and Nieman, T.A., Signal-to-noise enhancement by least-squares polynomial smoothing, Anal. Chem., 48, 705A, 1976. 

These studies indicate that perdeuteration can be achieved in proteins expressed in several different E. coli strains by growing selected cells in D2O media. Complete deuteration provides significant signal-to-noise enhancement in heteronuclear NMR assignment and structure determination experiments which use the amide proton for detection. 

E4. Ewing, G. W., Signal-to-noise enhancement in infra-red absorption spectrophotometry. Rev. Sci. Instrum. 42, 169-170 (1971). 

Hieftje G. M. (1972) Signal-to-noise enhancement through instrumental techniques, Anal Chem 44 81A-88A. 

Solid-state MAS NMR spectroscopy has had much success in examining amorphous insoluble polymers [59]. In recent years, however, there has been some debate on the reliability of quantitative data derived from CP experiments [60] and work on fossil fuels in particular has highlighted the problem [61,62]. Undoubtedly, the issues arise in the analysis of polymers as well [63-66]. While CP results in signal-to-noise enhancement and hence reduced accumulation times, carbon atoms present with no proximal protons tend to have their peak intensities reduced relative to other signals. Quaternary aromatic carbons are likely to suffer badly in this respect. The modulation of the dipolar interactions by the motion of some moieties can also introduce quantitative errors [67]. The rotation of the methyl group about its 3-fold axis of symmetry is a good example of this. Single pulse excitation (SPE) [60] however overcomes the problems that are associated with CP,... 

This has several advantages, one of which is that the new matrix usually is of smaller dimension than the original R matrix. A sensor array of 10 sensors with collinearity can be projected into a five-dimensional eigenvector space while mainly noise is removed. This signal to noise enhancement aids in the calibration performance. The new matrix is orthogonal and is easily inverted. To predict future samples, the response of the sensor array has to be projected onto the same eigenvectors in order to solve for the C matrix. 

Signal-to-noise enhancements using modified QCPMG pulse sequences are demonstrated by Siegel et al. 

The discussion of developments in instrumentation and measurement techniques that may be utilized for n.m.r. has been of necessity quite brief. Excellent reviews of signal-to-noise enhancement and double-resonance techniques and instrumentation have been given in Volume 1 of this series. 

Figure 9. Apodizations of chi experimental FT-NMR signal. (A) Fourier transform of the original unweighted free induction decay (F.I.D.) time-domain response to a 90 -pulse excitation. (B) Signal-to-noise enhancement F.I.D. weighted by the factor, exp(- r>LB-t), with LB = 3.0 Hz, before F.T.

The power of the Fourier transform as a processing tool is greatly enhanced by the judicious use of support routines. Most processing systems provide the user with a collection of mathematical functions that can be applied to the data before and after a Fourier transform. These functions can greatly affect the data obtained from various experiments. Mathematical functions exist for signal-to-noise enhancement, resolution enhancement, etc. Other mathematical operations can be performed on the data in conjunction with the... 

Signal-to-noise enhancement can be obtained by coherently adding successive echoes in the sequence. The optimum time for co-addition is easily shown to be 1.26 T2. Due to the generally small value of T2 in solids, however, this method does not result in an appreciable enhancement of the signal-to-noise ratio. 

The last expression shows that the signal- to-noise ratio is proportional to the square root of the number of data points collected to determine the ensemble average. Note that this same signal-to-noise enhancement is realized in boxcar averaging and digital filtering, which we describe in subsequent sections. 

Signals and Noise 110 5A The Signal-to-Noise Ratio 110 5B Sources of Noise in Instrumental Analyses 5C Signal-to-Noise Enhancement 113 Questions and Problems 124... 

R Bennett. Applications of a modulated laser for FT-Raman spectroscopy. Part 2. Signal-to-noise enhancement and removal of thermal backgrounds. Spectrochim Acta 51A 2001—2009, 1995. 

---