Chromatogram secondary reactions

The chromatograms of the liquid phase show the presence of smaller and larger hydrocarbons than the parent one. Nevertheless, the main products are n-alkanes and 1-alkenes with a carbon number between 3 to 9 and an equimolar distribution is obtained. The product distribution can be explained by the F-S-S mechanism. Between the peaks of these hydrocarbons, it is possible to observe numerous smaller peaks. They have been identified by mass spectrometry as X-alkenes, dienes and also cyclic compounds (saturated, partially saturated and aromatic). These secondary products start to appear at 400 °C. Of course, their quantities increase at 425 °C. As these hydrocarbons are not seen for the lower temperature, it is possible to imagine that they are secondary reaction products. The analysis of the gaseous phase shows the presence of hydrogen, light alkanes and 1-alkenes. 

Contaminants may arise from impure starting materials, incomplete reactions and secondary reaction products. A knowledge of these factors serves to limit the list of probable contaminants to a small number. Tentative identifications of some of the contaminants shown as minor peaks in the chromatograms were assigned by matching their retention times (or retention temperatures) with those of probable contaminants. In the case of the six carboxylic acids of Table II, the contaminants are known to be carboxylic acids, since the method of purification involves repeated precipitations as the ammonium salts. The tridecanedioc acid observed in the octadecanedioc acid (compound 10 of Table IV) is considered the source of the lower homolog impurity to-(p-chlorophenyl)-octadecyl bromide (compound 6 of Table IV). 

The possibility that more of the reaction product Ado had remained on the column was ruled out by using different mobile phases to elute all bound material. The chromatograms accounted for all the products. Since we had not expected any side reactions, we quantitated the yield of reaction products on the basis of area, assuming the presence of only adenosine-containing compounds. The formation of inosine, with a 50% reduction in extinction coefficient, could account for the apparent lack of recovery. Therefore, we considered the presence of secondary reactions. Either AMP had been converted to IMP, or adenosine was converted to inosine (Ino). By comparing the retention time of the third peak to authentic standards, we ruled out IMP as a product, and thus the identity of peak 3 was established as inosine. This led us to conclude that the commercial preparation of alkaline phosphatase was contaminated with a second activity, adenosine deaminase. 

Secondary reactions are the result of enzymatic activities present in the sample that lead to destruction of the substrate and/or the formation of additional products, which can alter the appearance of the chromatogram. 

Next, a second and third series of reaction mixtures should be prepared, with enzyme added at concentrations of half and twice the value used in the first. These reactions are started and sampled, chromatograms are obtained, and the data are plotted as a function of reaction time. At this early stage in the optimization of the assay, it is advisable to continue sampling one of the incubations until the rate of product formation becomes nonlinear or the amount of substrate present is exhausted. This prolonged incubation provides information about the extent of the primary reaction and also allows any secondary reactions to take place and form enough products to be detectable. 

A careful visual inspection of the chromatogram should be sufficient to indicate the presence (or absence) of any peaks other than the substrate and the product. If only peaks of the latter type are present, the absence of secondary reactions involving either substrate or product is suggested. Second, a visual estimation of the area of both the substrate and product peaks should indicate whether the two are equal (assuming an equivalence of their extinction... 

The chromatogram obtained from each analysis provides information about product formation and loss of substrate. In the absence of secondary reactions, the two values should be additive. 

The reaction mixture contained the substrate L-tyrosine. Benzyloxyamine was added to inhibit any secondary reactions catalyzed by the enzyme aromatic L-amino acid decarboxylase, an activity often present in these samples. Chromatograms of samples taken during an incubation are shown in Figure 9.1 B, a zero-time control with a single peak of tyrosine, and Figure 9.1C, after 20 minutes of incubation showing the peak of Dopa formed as a result of enzymatic activity. 

The flash pyrolysis of starch has not yet been reported. In this technique, a thin film of polymer is heated rapidly (in one second, or less) to about 600", and the resultant, volatile compounds are immediately swept onto the gas-chromatographic column for analysis. The effects of thermal gradients in the sample, the diffusion of products, and secondary reactions are thus minimized. In the field of synthetic polymers, flash pyrolysis provides a convenient and rapid method of analysis, because the chromatogram produced is characteristic of the material. Chromatograms from the flash pyrolysis of cellulose have been described. ... 

The results showed that some of the expected reaction products were formed. Figure 2a shows the time profiles of NMP, NMS and succinimide, while Figure 2b shows the corresponding plots of product concentrations versus the concentration of NMP consumed. The latter plots clearly show that NMS was a primary reaction product, whereas succinimide was a secondary one. The carbon balance of NMS production is 55 1 %. This indicates that other primary reaction products have to be formed. Figure 2 shows that one unidentified compound was a primary product. Furthermore, the HPLC chromatograms contained a lot of unidentified and unresolved peaks (Figure 3). Therefore, an on-line mass spectrometer was designed in order to identify more reaction products. 

Secondary amine-functionalized polystyrene was prepared by normal addition of N-benzylidenemethylamine to PSLi (A n = 2100gmor ) in benzene (eqn [21]). No unfunc-tionalized polystyrene was observed by TLC on silica gel plates using benzene as eluent. The SEC chromatogram of the functionalized polymer showed no indication of dimer formation, in contrast to the analogous functionalization reaction with N-benzylidenetrimethylsilylamine that formed 19% of dimeric products discussed in the previous section. The Mn of the functionalized polymers determined by SEC was appreciably smaller compared to that of base polymer due to interactions of the functionalized polymer with the SEC columns, which could be deduced from the larger retention volume of the functionalized polymers compared to that of base polymers and tailing of the functionalized polymers. The functionality determined by end-group titration was 96%. 

If the pH and concentration of each ligand in solution are known, then these reactions and constants can be used to determine the equilibrium concentration of each metal species. In those instances in which the solution is also a liquid chromatographic eluent, such qualitative and quantitative information relates to the different types of eluite forms that are present in the mobile phase—free and complexed metal. This information is significant because the retention that is observed for a particular eluite is dependent upon the relative proportion of each different eluite forms present in solution. Those readers having utilized one of the more well known modes of secondary chemical equilibria (i.e., acid-base, ion-pairing, solute-micelle) may be well versed in how changes in the composition of the mobile phase can influence the relative proportions of eluite forms, and ultimately, the overall appearance of the chromatogram [33-35]. 

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