Correlated spectroscopy artifacts

Hess, ST and Webb, WW, Focal volume optics and experimental artifacts in confocal fluorescence correlation spectroscopy. Biophysical Journal 83 (2002) 2300-2317. 

Linear prediction is a method to directly obtain the resonance frequencies and relaxation rates from time domain signals, which are a superposition of exponents, by solving the characteristic polynomials. Phases and intensities are calculated interactively using a least-squares procedure. The correlation spectroscopy of a two-dimensional NMR spectrometer employs several specific programs such as RELAY and TOCSY. The recognition of response peaks, the isolations of signals from noise and artifacts, and the spectral position (e.g., chemical shift) are all carried out by computers. 

Symmetry relationship of cross peak locations has been used for improving the quality of correlation spectra for quite a long time in NMR spectroscopy both for diagonally [21] and laterally symmetric spectra [22]. Such data processing procedures have their advantage but may introduce artifacts and remove real information and therefore should be used with caution [10]. 2Q-HoMQC spectra can be symmetrized directly using the appropriate symmetry function [33], but most commercial software do not provide such option. Also, fine structure of the direct correlation peaks in 2Q-H0MQC spectra is antisymmetric in the SQ dimension which requires extra attention. 

In addition to the Tal-e Malyan and Tepe Yahya artifacts, objects from two other archaeological sites were included in the analysis. The two selected pieces from earlier periods at Ali Kosh and Choga Safid were included to attempt to correlate the samples in this investigation with those analyzed by Renfrew and coworkers (8-10) by optical emission spectroscopy. 

Branca et alP reported a detailed and understandable analysis of the evolution of various coherence orders in a Correlated 2D spectroscopy revamped by asymmetric z-gradient echo detection (CRAZED) like pulse sequence, used to select a signal from intermolecular multi quantum coherences (iMQCs). Because the signal to-noise-ratio of iMQC is much lower than the signal from conventional single quantum coherence (SQC), an optimization of experimental parameters is a necessity when measurements are made with iMQC. For this purpose a phase cycle is shown that not only allows a simpler selection of a particular quantum coherence order, but also removes receiver artifacts. 

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