Peak identification methods

The specialities of chromatographic behaviour of cypermethrin, permethrin, X-cyhalothrin, deltamethrin and fenvalerate were investigated in this work. Gas chromatographic determination was cai ry out with use of packed column with stationai y phase of different polarity (OV-101, OV-210 OV-17) and capillary and polycapillary columns with non-polai ic stationary phase. Chromatographic peak identification was realized with attraction GC-MS method. 

Figure 13.10 LC-LC chromatogram of a surface water sample spiked at 2 p.g 1 with ati azine, and its metabolites (registered at 220 nm). Conditions volume of sample injected, 2 ml clean-up time, 2.60 min ti ansfer time, 4.2 min The blank was subtracted. Peak identification is as follows 1, DIA 2, HA 3, DEA 4, atrazine. Reprinted from Journal of Chromatography, A 778, F. Hernandez et al, New method for the rapid detemiination of triazine herbicides and some of thek main metabolites in water by using coupled-column liquid cliromatography and large volume injection , pp. 171-181, copyright 1997, with permission from Elsevier Science.

Figure 15.1 Separation of pesticides from butter by using LC-GC-ECD. Peak identification is as follows 1, HCB 2, lindane 5, aldrin 7, o,p -DDE 10, endrin 11, o,p -DDT 13, p,p -DDT peaks 3, 4, 6, 8, 9, 12, 14, 15 and 16 were not identified. Adapted from Journal of High Resolution Chromatography, 13, R. Barcarolo, Coupled EC-GC a new method for the on-line analysis of organchlorine pesticide residues in fat , pp. 465-469, 1990, with permission from Wiley-VCH.

As a consequence of the development of extraction methods for STA based on mixed-mode SPE columns, as well as of the recent introduction of instruments for the automated sample preparation allowing efficient evaporation and derivatization of the extracts, full automation of STA methods based on GC-MS analysis is also available. It needs GC-MS instalments equipped with an HP PrepStation System. The samples directly injected by the PrepStation are analyzed by full scan GC-MS. Using macrocommands, peak identification and reporting of the results are also automated. Each ion of interest is automatically selected, retention time is calculated, and the peak area is determined. All data are checked for interference, peak selection, and baseline determination. 

R< is used in the same manner as is Rt except that it is the retention time of components in the GC or HPLC column (see Figure 13.6). The time is measured from the time of injection to the time the top of the peak elutes from the column. Another approach is to include a compound that is not retained by the solid or liquid phase in the injection and its peak used as the starting time (0 time) for measuring the time for each peak to exit the column. Two compounds exiting the column at the same Rt will be assumed to be the same compound. Often, Rt values are used for identification, although only a spectroscopic method can truly be an identification method because two different molecules can have identical Rt values. 

A PDA detector provides UV spectra of eluting peaks in addition to monitoring the absorbance of the HPLC eluent like the UVA is absorbance detector. It is the preferred detector for testing impurities and for method development. PDA facilitates peak identification during methods development and peak purity evaluation during method validation. Detector sensitivity was an issue in earlier models but has improved significantly (more than ten-fold) in recent years. ... 

Enantiomeric assay determinations are typically applied to characterize racemic mixtures using the normalized peak area (area%) calculation procedure. The selectivity solution is utilized to demonstrate the separation capability in the method and to allow peak identification. A suggested sample injection sequence can be... 

Since the work of Manley and Shubiak (182), who were the first to apply HPLC to anthocyanin analysis, numerous HPLC techniques have been developed for the separation and quantification of anthocyanins and anthocyanidins. Nowadays HPLC has become the method of choice, because it offers the advantage that it is a rapid, sensitive, and quantitative method. For the peak identification and quantitative evaluation of chromatograms, the use of pure anthocyanin standards is recommended however, only a limited, but constantly increasing, number of substances is avail-... 

All compendias [5-7] specify use of a liquid chromatographic method to determine the eight known rocuronium bromide impurities. The chromatographic method corresponds to the chromatographic method used to determine rocuronium in bulk drug substance, as detailed in Section 2.3.1. For the purpose of analyzing impurities, the RS used is the RS of rocuronium that is intended for peak identification, where the identification standard contains impurities of rocuronium bromide and rocuronium bromide itself. 

There are a variety of techniques currently in use to aid in the identification of sample components. Most techniques, such as spiking and the enzyme peak shift method, are used to confirm the identities of components thought to be in the sample. If, however, the identity of the sample is truly unknown, a combination of techniques is needed to provide a unique fingerprint. ... 

As a first approximation, the most commonly used method of peak identification is that of matching the retention times, or occasionally capacity factors, of the sample components with those of standard reference... 

The relative retention of a compound on two different systems can also be used for tentative peak identification. This method is based on the premise that the possibility of different compounds showing identical behavior under different conditions is relatively small. Thus, use of different detectors, for example, fluorescence and UV detection, or different techniques, such as chromatography and electrophoresis, will help to confirm the identities of peaks in a sample. 

This chapter describes the more commonly used methods of quantitation, with brief discussions on the theory. For more information on the use of computers and quantitation, see Braithwaite and Smith.10 An excellent account of chromatographic integration methods for peak identification, validation, and quantitation is provided in the text by Dyson.11... 

Determination of free 4-hydroxy-2,3-trans-alkenals by HPLC Esterbauer (1982) has developed a procedure for the qualitative detection and quantitative measurement of steady-state concentrations of free hydroxyalkenals (specifically HNE) in tissues, tissue extracts and lipid containing foodstuffs. Their method utilizes UV-detection of the free aldehyde at its 220 nm UV-absorption maximum and peak identification was confirmed by mass spectrometry. An effective purification and concentration step is employed using dichloromethane to extract hydroxyalkenals from samples trapped on Extrelut columns. The samples are subsequently purified by solid-phase extraction on octadecyl-bonded silica (ODS) disposable cartridges and then analysed by HPLC. 

Sample pretreatment, sample compatability, along with examples of auxiliary methods of peak identification and sensory evaluation are discussed. Coupled techniques such as LC/HPLC, and HPLC/GLC/MS systems are discussed using specific examples. 

Various procedures described by Crippen and Smith (5) are available for identifying components in a chromatogram. Because of the limitations mentioned above, the choice of method was restricted. Peak identifications for this sample relied on cleanup and preliminary separation by column adsorption chromatography with activated alumina and Florisil, use of the chlorine- and sulfur-specific microcoulometric detector, and parallel injections onto three or more columns containing liquid substrates varying widely in polarity. 

A 15 mM borate buffer has been extensively validated 113] for the analysis of a wide range of acidic drugs, excipients and raw materials. Internal standards were used to improve injection precision and peak identification. Fig. 3.5 shows a separation of warfarin with two reference compounds P-naphthoxyacetic acid and aminobenzoic acid. Extensive method validation included linearity, sensitivity, solution stability, recovery... 

Migration time precision may be used for peak identification and is important in assessing the overall performance of a method, since many other parameters impinge on its reproducibility. Recent studies have demonstrated that not only is CE capable of exhibiting... 

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