Peak Separation ghost

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. 

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. 

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. 

Trifluoroacetate TFA is a common, volatile buffer additive for the separation of proteins and peptides. Depending on quality and batch it can give rise to ghost peaks. General properties of TFA Y. Chen et al., J. Chromatogr. A, 1043, 9 (2004). 

Baker [577] used an FFAP coliurm for direct injection of dilute aqueous solutions of acids (FFAP is a reaction product of polyethylene glycol 20,000 and 2-nitrophthalic acid developed by Varian Aerograph). The acetic acid peak was not clear and the ability of this column to separate normal and iso fatty acids was not reported. Van Huyssteen [608] successfully used a Chromosorb 101 column coated with 3% FFAP for separation of volatile acids by direct injection of synthetic aqueous solutions and anaerobic digester samples, which were first centrifuged and acidified to pHl-2 with hydrochloric acid. His column afiected complete separation of the Cj-Cs straight and branched short-chain fatty acids from synthetic aqueous solutions, but less sharpened peaks were obtained from anaerobic digester samples. The response with acetic acid approximated that of the other acids additional peaks, probably alcohols, appeared between the acid peaks. To eliminate ghosting l-2pL water was injected between samples. 

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