Spectral homogeneity

HAP, COHAP and COD were measured through slabs of varying thickness from 2 to 10.2 mm of normal chicken breast tissue, and chicken breast with chicken skin on the surface. Chicken breast and skin tissue were used in the model due to their spectrally homogenous nature. Normal fresh chicken breast was obtained and a small section cut varying thicknesses between 2 and 10.2 mm (2.0, 3.1, 5.0, 5.9, 8.7, 10.2 mm) with other dimensions approximately 20 x 20mm. A small section of skin tissue was also cut (to 1.1mm thick). The samples were stored in a refrigerator and warmed to room temperature before use. 

Also the spectral homogeneity of the peak of interest must be taken into consideration. Diode array spectra at least three points across the peak should be taken to ensure the peak is spectrally homogenous see Figure 8-14. If the peak is not spectrally homogenous, the overlay of the spectra will show... 

Alternatively, the results from the gradient runs for each sample can be inputted into Drylab, ACD, or Chromsword for further optimization (see Sections 8.5.6.11). For the predicted experimental conditions (i.e., gradient slope, temperature, flow rate), if desired selectivity and resolution can be obtained, an experiment can be run for verification. The peak purity for the main analyte (MS and DAD detection) should be checked in the verification run. If the desired selectivity and/or the target analyte are not spectrally homogeneous, go to Step 6, Figure 8-37. 

Step 6 Screen Different Columns/Mobile Phases Using an Automated Method Development System or Column Switcher. If the desired selectivity is not obtained or the peak is not spectrally homogeneous from Step 5, then different columns (two to six) and mobile phases can be screened using a column switcher. The typical mobile phases that could be screened include acetonitrile, methanol, and acetonitrile/methanol mixtures using the same "pH... 

Using this optimized method shown in Figure 8-49 that starts at 25v/v% acetonitrile, LC-MS studies were performed to determine the [M -i- H]+ ion of the impurity that has been resolved from the main peak. The mass spectrum of Product M was taken and was shown to be spectrally homogeneous. The mass spectrum of the impurity (RRT 1.04) that has now been resolved from the main peak was also taken. The UV and the total ion chromatograms are shown in Figure 8-50. This impurity, RRT 1.04, has the same [M -i- H]+ ion that was co-eluting with the main component in the initial separation on the C8... 

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