Correlation peaks

Figure 19.13 Conjugation to KLH often can cause precipitation due to the high-molecular weight of the carrier protein. The conjugation of [Met5]-enkephalin to KLH yields a soluble immunogen if the level of EDC addition is about 0.1 times that typically used with BSA as a carrier. This figure shows the gel filtration pattern on Sephadex G-25 after completion of the crosslinking reaction. The first peak is KLH and the second peak is excess peptide. Depletion of the peptide peak correlates to hapten-carrier conjugation.

Once an appropriate, MS-friendly, LC method is developed, information such as the UV spectrum and percent peak area can be used to establish peak correlation between LC/UV and LC/MS methods. 

FIGURE 18 A challenging case in which peak correlation between two LC methods cannot be achieved based on the percent of peak area and the UV spectra of the peaks (courtesy ofWaters Corp.). 

From the brief theoretical discussion that follows, it is clear that even a very simple molecule can give an extremely complex spectrum. The organic chemist takes advantage of this complexity when matching the spectrum of an unknown compound against that of an authentic sample. A peak-by-peak correlation is excellent evidence for identity. Any two compounds, except enantiomers, are unlikely to give exactly the same IR spectrum. 

Exchange peaks correlate one molecule with a different molecule, whereas NOE peaks correlate through space within the same molecule. The NMR timescale for this exchange (AS = 5.11-4.54 = 0.57 ppm Av = 0.57 x 500 = 285 Hz) can be calculated as 1/(2.22 x Av) = 1.58 ms. Because we see sharp peaks for the glucose-1 resonances of both forms of lactose, the lifetime of each state must be much longer than 1.58 ms. 

Proton and carbon 13 NMR spectra were obtained from the three commercial samples. A series of unknown spectral components were observed in product A at 3.68 ppm, 3.98 ppm, 4.08 ppm, 4.15 ppm, 5.05 ppm, and 5.17 ppm. Comparison of the unknown peaks with the spectra of MAGs indicated that most of the observed peaks correlated with those present in the spectra of MAGs. An exact assignment of the spectra was not attempted as many forms of MAGs are possible. Observation of the spectral region of the olefinic protons revealed that the three samples were... 

Figure 6. WFP-2L values compared to the GIPS2 and Vostok ice-core records for similar time periods. 3 -order polynomial best-fit lines are shown for the WFP-2L and Vostok isotope records. A 3-point running mean (thick line) is shown for the GISP2 record. This reduces the GISP2 record to a resolution similar to the WFP-2L s resolution (WFP-2L has 51 points while the GISP2 record has 160 points). 5 0 values are not available for the Vostok record. The speleothem isotopes are plotted relative to distance from base. Bars on the dates represent vertical sampling range and they have been lined up with the compared chronologies. One possible peak-correlation scenario is shown (dotted lines). The GISP2 data are from Grootes et al. (1993), Meese et al. (1994) and Stuiver et al. (1995). The Vostok data is from Chappellaz and Jouzel (1992).

The most sensitive techiuques are based on the reversibility degree of the redox reactions of certain reactants present in solution. The reactions of TCNQ [60] and ferrocene derivatives [47,53] can be carried out quite reversibly on the freshly formed surfaces of encapsulated ceramic HTSC electrodes and high-quality films in dry acetonitrile. On addition of water, the reversibility is upset due to the formation of low-conductivity degradation products on the surface. The increase in the potential difference between anodic and cathodic peaks correlates with the degradation rate. According to [484] reversible responses to similar reactants can also be obtained on electrodes made of high-quality ceramics. 

A neat reference mixture was prepared that contained 17 pure NHCs plus pyridine and quinoline as retention index markers (Table 1 Fig. 2). Relative amounts were adjusted to give approximately equal peak sizes. Triplicate analyses were performed on the 65 °C headspace above this mixture and above several wastewaters. To minimize any effect of column aging on peak retention times, the reference and wastewater replicates in each test series were alternated. Reproducibilities were excellent with standard deviations averaging 0.12 retention units overall and 0.05 retention units for the reference mixture. Reference-peak to sample-peak correlations were performed by a variety of statistical procedures including z tests. Student-t tests and, later, the procedure described in Section 3.2. 

Although most of the compounds in the reference mixture were alkylpyridines, a class of NHCs known to be present in oil shale wastewaters (]3, very few peaks correlated with the reference compounds. A typical example involving Oxy-6 gas condensate is shown in the Table 1 (column VI). Only 4 out of 17 compounds were correlated, many of the simplest (and most likely) components (e.g, methyl- and ethyl-pyridines) being excluded. Furthermore, when the Oxy-6 gas condensate was... 

MALDI-TOF was successfully utilized for determination of the molar mass of low molar mass HA samples [283]. Fig. (16) shows a MALDI-TOF spectrum of a HA fraction separated using an SEC system. The MALDI-TOF spectrum clearly shows the major mass differences between the peaks corresponding to a mass of the disaccharide repeating unit of HA, (378 Da), and the minor peaks correlated to the molar masses of the two monosaccharide components of HA. 

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