Relative retention time degradation products

All of the initial CGC organobromine degradation products assignments were based on the use of relative retention time standards. The relative retention times for the partially brominated degradation products were established either by the synthesis of the expected degradation products or by the use of selective debromination reactions. 

In addition, HPLC can be employed as a reference method for unknown degradation products where an unknown degradation product can be identified based on its the retention behavior in RP-HPLC and the corresponding relative retention time is determined (retention of degradation product/reten-tion of API). 

Once a decision has been made to identify an unknown, the next logical step is to evaluate all known process-related impurities, precursors, intermediates, and degradation products. By observing the relative retention times (HPLC) of all known process-related impurities, precursors, and intermediates (if available), one can quickly determine whether or not the impurity of interest is truly unknown. If the relative retention time of the unknown impurity matches that of a standard, the unknown can be identified using HPLC with ultraviolet (UV) photodiode array detection as well as mass spectrometry (MS) detection. The identity can be considered confirmed by correlating the retention time, UV spectra, and mass spectra of the unknown impurity with that of the standard. The time and energy saved by analyzing data that may be already available can be considerable. 

In order to account for column degradation reference substances are often added to the unknown sample and so-called relative retention times (RRT) are used instead of the absolute retention times (RT) for the analyte. The retention times of the analytes are thereby calculated in relation to the retention time interval for the standards. Requirements placed on RRT standards are identical to those for internal standards for the quantitative GC analysis. The procedure adopted is based on the assumption that retention times for the standards are affected by column ageing in the same way as those for the analytes, thus ensuring retention time stability. In addition, standards must have sufficient thermal stability at 550°C and should not undergo any reactions with pyrolysis products of the sample. They should also exhibit characteristic mass spectra that permit unambiguous identification. If standards are to be used for quantitative evaluation on the basis of peak areas, then it must be assured that these are not also being formed by pyrolysis of the polymer matrix. A typical RRT reference solution is made up by dissolving 2.0 mg anthracene and 10.0 mg dibenzo[a,/i] anthracene (DBA) in 20 mL dichloromethane. 

Protease-liberated flavoprotein from TX-20 algae was relatively less active in stimulating lindane as compared to the case with DDT. As illustrated in Figure 4, one major and two minor degradation products with short retention times were formed by the flavoprotein, whereas one major product was formed when FMN was added to the incubation mixture. When lindane was incubated with buffer or buffer + FMN no degradation products were detected by GLC analysis. The major degradation product formed by TX-20 had the same retention time as y BTC in two GLC systems (2.3 min, A in Fig. 4 and 3 min on QF-1 at 130°C). 

Previous studies (18) on the stability of A -tetrahydrocannabinol in acidic media below pH 4 monitored by GLC demonstrated an apparent biphasic semilog-arithmic plot of undegraded 1 against time either there was formed an intermediate which has the same retention time as 1 that also gave rise to the observed products or there was a relatively rapid equilibration of A9-tetrahydrocannabinol 1 with another compound and slower further irreversible degradation of one or all of these compounds. (The studies were performed with l c-labeled and non-labeled 1). Since the possible reasons why this problem was not solved were that the specific activity or the concentration were too low, additional studies (16) at concentrations about 10 mg/1 of HPLC purified 1 were carried out in 20% ethanolic solutions (0.1N HC1). The GLC (OV-17) analyses of the degraded products are summarized in Table 2. The retention times of the different compounds were the... 

Samples can be pyrolysed at a series of temperatures between 400 and 1000 "C and the change in degradation behaviour as shown by the (1) appearance temperatures of various peaks and (2) relative abundance of products as a function of temperature noted [12, 13]. Changes of the most characteristic breakdown products versus temperature can also be plotted. For homopolymers the temperatures at which degradation products are first obtained may be more distinctive than the retention times of the products. 

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