Retention time comparison

GC-MS analysis has become standard practice in semiochemical research. There is, however, a real danger that information based exclusively on the results of computerized library searches without mass spectral and retention-time comparison with authentic synthetic material can be introduced into the literature. This could be problem especially in mammalian semiochemistry, because researchers often are faced with the problem of having to identify large numbers of compounds of which many may have very uninformative mass spectra. A critical reader of the original publication could still be aware of the unverified nature of some of the information, but this may not be pointed out in later references to the work. 

As previously discussed, K IDS does not always provide accurate quantitative data. Therefore, SFC was performed on the macromer. The monomer volatility is not a problem in these studies. Figure 5 is chromatogram of the MMA macromer. The first large broad peak is due to monomer. Identification was based upon retention time comparison to a standard. Each of the corresponding peaks are due to the oligomers up to the 15-mer. We attribute the minor distribution to (VIII). 

Figure 9 is a portion of the chromatogram of the extract from a cured paint film. The coating was extracted at 400 atmospheres (atm) at 125°C for twenty-minutes. The chromatographic conditions are described in Figure 9. The peak eluting at about twenty-five minutes corresponds to Tinuvin 440 (XIII) which was identified based upon retention time comparison to an authentic standard. Tinuvin 440 is a HALS and does not have a strong chromophore, but is easily detected using FID. The last peak appearing at thirty-four minutes is due to Tinuvin 900 (XIV), also identified by retention time comparison. Ve did not identify the peak at twenty-one minutes.

Once the monomers have been identified, in order to utilize rel. (4.3.20) to calculate n(A), all the trimer peaks in the pyrogram must be identified. Theoretically, there are eight different trimer peaks in a copolymer system AAA, AAB, BAA, ABA, BAB, BBA, ABB, and BBB. Their identification is not always simple. However, the AAA and BBB peaks can be identified easily. Since the trimer BAA and AAB have the same molecular mass, they are difficult to distinguish, but the expression for n(A) requires only the sum Nbaa + Naab and they do not need to be differentiated. Pyrolysis of an alternating AB copolymer will allow distinguishing the ABA and BAB, which are the only ones, generated in this case. However, peak identification also can be achieved from retention time comparison or other spectra characteristics. 

Retention time comparisons depend greatly on the constancy of the solvent... 

The C8 products were analyzed on a AgN03/benzyl cyanide column which discriminates between alkenes and alkanes, and on a SE-30 column which discriminates according to boiling point. These two columns clearly distinguish the alkenes from the alkanes. The products were identified by retention time comparison on both columns with C8 standards (Table I). Identification of the more abundant olefins was confirmed by mass spectrometry. 

HPLC can be used as a qualitative or quantitative technique. Qualitative information can allow a substance to be identified on the basis of retention time comparison between a standard and the sample. Alternatively, and more definitively, the use of a mass spectrometric detector enables the molecular weight of eluting components to be determined and, as long as those molecular weights are unique, unambiguous identification is possible. When used quantitatively, HPLC can employ external or internal standards to generate a standard curve. Then, the peak area of the sample peak on the chromatogram can be used to obtain a concentration. 

Peak identification and potential coelution of organic acids are not always given due consideration, although AEC has much inferior separation efficiencies compared to GC. Ideally, organic acid identification, which is typically done by retention time comparison, should be confirmed with another independent method. Several publications investigating rain and atmospheric precipitation validated their AEC results with either lEC or Other... 

Compound identification in lEC is accomplished by retention time comparison and coelution and/or incomplete separation of organic acids can be expected due to the low separation efficiency of lEC compared to GC, for example. Organic acid pairs known to coelute are fumaric/acetic acid and also succinic/glycolic acid. " Ideally the identity of a compound should be confirmed with an independent analytical method. It is therefore surprising that only few of the environmental methods listed in Table 13.6 even touch on this issue. ... 

Fractions 3 and 4 from the tar trap tar, which primarily contained polycyclic aromatic hydrocarbons and their alkylated derivatives, were combined and subfractionated on a silica gel column. In sequential elution, toluene eluted 46 percent of the mass (subfraction A), propanol eluted 48 percent (subfraction B), methanol eluted 3 percent (subfraction C) and 3 percent was recovered by washing the silica gel with tetrahydrofuran (subtraction D). The toluene subfraction was found by GC/MS analysis to consist of a series of PAH, both parent compounds and numerous methylated derivatives. In addition, the heterocyclic compound dibenzothiophene was present as a major peak. Tentative identifications are listed in Table IX. Compounds whose identifications were confirmed by GC retention time comparisons with standards are noted. Although the identities of many of the individual PAHs have not been confirmed, it is clear that most of the subtraction is PAH in nature. 

Retention time comparisons depend greatly on the constancy of the solvent delivery system and are less sensitive than the sample-reference mixture injection alternative. 

K after 1215 min. The apparatus was cooled to room temperature, and the headspace gases and liquid phase analyzed by GC, giving the results shown in Table 15.1. Gas-phase products were identified by comparison of their retention time with authentic samples. Liquid-phase products were identified by retention time comparison and GC-MS. The recovered liquid phase was pale blue-green with most of the metal collected in a sticky mass. 

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