Ghost peak

Note that the presence of modulation, or ghost peaks, is not an absolute indication of a problem within the machine-train. Couple effects may simply increase the amplitude of the fundamental mnning speed and do little damage to the machine-train. However, this increased amplitude will amplify any defects within the machine-train. 

The symptoms of column contamination include irregular peak shape, loss of resolution, loss of retention, irregular or noisy baseline, and ghost peaks from semivolatile materials of a previous run or from sample decomposition. Some of these problems can be the result of a contaminated injector. 

Pure 2D absorption line shapes are readily obtained in heteronuclear 2D /-resolved spectra. The incorrect setting of 90° and 180° pulses can, however, cause ghost peaks that can be removed by a phase cycling procedure, appropriately named Exorcycle (Rutar, 1984b). A... 

Quadrature images Any imbalances between the two channels of a quadrature detection system cause ghost peaks, which appear as symmetrically located artifact peaks on opposite sides of the spectrometer frequency. They can be eliminated by an appropriate phase-cycling procedure, e.g., CYCLOPS. 

Gaussian peaks, 3, 8 Gentamicin, 282, 286 Gentian root, 294 Gentiopicroside, 294 Gentisin, 294 Ghost peaks, 188... 

Y. Egi and A. Ueyanagi, Ghost Peaks and Aerated Sample Solvent, LCGC 1998,16. 112. 

Mounts et al. proposed a binary gradient of chloroform/THF (1/1) on the one hand and methanol/NH4OH/C (92/7/1) on the other hand (79). According to Abidi et al., incorporation of pure THF to a mobile phase consisting of C/M and ammonium hydroxide enhances the separation of PC from PA (80). However, impurities were often found in THF, causing severe ghost peak interference with PL analytes. The use of tertiary butyl methyl ether (tBME) instead of THF eliminated these problems. 

At cold spots the analytes can adsorb to the surface material and only a fraction will reach the detector. Subsequently, the adsorbed compounds can result in ghost peaks in later analyses. Transfer lines from for example, a TD instrument to the GC must be insulated and heated to avoid cold spots . The optimal temperature of the surfaces depends on the stability of the component, pressure, vacuum, etc. Some GC instruments have ceramic insulators at the inlet of the transfer line from for example, TD instruments and this material may act as a cold spot if the line is not heated at the inlet... 

Problem 7 Ghosting peaks occur when injecting only solvent. 

Problem No. 19 Ghost Peak (Carry Over Peak)... 

This effect and similar ones are sometimes responsible for unwanted, unexpected peaks in chromatograms, and then they are called ghost peaks or pseudo peaks. A recent review of this entire subject55 calls them system peaks, and it is a good source of further details and references. 

It should be noted that if an ion fragments during the analysis, it is possible that its m/z ratio is such that its qz value is higher than the resonant ejection value. If, later on, by increasing V, it reaches the stability limit (qz = 0.908) and is ejected, it will then be detected at a wrong m/z, as the data system expects it to be expelled by resonance. Its apparent m/z will be higher than the true one. These ghost peaks will occur more if the resonance frequency corresponds to a lower qz value. 

Another experimental artifact of FFF is the occurrence of ghost peaks . Granger et al. speculated for the case of A-Fl-FFF that such peaks can occur if the sample does not reach its steady state concentration distribution and is thus transported by pure convection in the flow field which can occur at high flow rates [248]. The other peak is that for the separation by diffusion and fits well with theory. 

IPRs ADDED ONLY TO SAMPLE SOLUTION AND GHOST PEAKS... 

Note that it is a common practice to dissolve the analytes to be separated in the mobile phase. In fact, the injection of the sample in a solution whose composition differs from that of the eluent would create a disturbance at the top of the column that will migrate down the column. The lack of detectable eluent component in the injected solution would create a negative system, perturbation, or ghost peak because the concentration of that component is lower compared to the initial conditions under which the baseline was recorded. Obviously the retention time of the system peak is that of the component under the experimental conditions used in the chromatographic run [28,29]. System peaks are also very useful for indirect detection [30], as will be explained in Chapter 13. 

---