Coeluting components

Response suppression or enhancement effects may be exerted by any coeluting component entering the API source via LC. Some mobile-phase additives are known to suppress or enhance analyte response. It is useful to discriminate between effects due to the analytical system, e.g., mobile-phase composition, source parameters, and effects due the actual analyte matrix. 

Check the Photo diode array (PDA) peak purity of any suspicious peaks. Take spectra at five points across the peak. All the UV spectra should overlay if it is a pure peak. This may help you identify any coeluting components. 

The high selectivity of mass spectrometry detection allows one to identify coeluting components. 

Peak Parking Another approach to acquiring complete information in a narrow peak is to extend the analysis time over peaks of interest. In this approach, termed peak parking or variable-flow chromatography, the column head pressure, and hence the flow rate, are reduced instantaneously [3,4], With this approach, it is possible to perform higher-resolution narrow mass scans and acquire MS/MS scans on all coeluting components in a single narrow peak. 

The combination provides enhanced sensitivity, selectivity, speed of analysis, an opportunity for automation, feasibility of quantification of coeluting components or isobaric compounds, and use of the stable-isotope labeled analogs as internal standards. 

The incomplete chromatographic separation of the isomers in the rat urine and the similarities of the MS" spectra of the coeluted components resulted in difficulties in the structural elucidation of metaboKtes in rat urine. These coeluted components were distinguished on the basis of the metaboKc pathway and biogenic feature. The metabolite Mil was used as an example to iKustrate the analytical procedure. 

The spectrum of the unknown compound to be identified should not contain any spectral impurities as caused by coeluting components. If a spectrum is known to contain a spectral impurity, it should be corrected for this impurity before the comparison with the standard spectra. Corrections for coeluting impurities are very difficult. If the impurity does not coelute completely, identification may still be possible, depending on the concentration and elution time of the impurity, relative to the main peak. 

In a sample with many components, some compounds will coelute, partly or completely, depending on the complexity of the sample and the peak capacity of the column. With mass spectrometric detection, even coeluting components can be identified. 

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