Total absorption chromatogram

Within the front-end processor is an integrator that will integrate the output of the log-ratio-amplifier over the period between the beginning and end-of-scan pulses. This is the equivalent of total ion current in GC/MS the value in LC/UV,VIS is termed a total absorption chromatogram or TAC. 

Eqn.(5.27) shows that the total absorption is the result of the contributions of a series of factors which depend either exclusively on the wavelength (a. factors = spectra) or on the time (Cj factors = elution profiles). The individual factors may be obtained with PCA, but an unambiguous solution for the mathematical problem may only be obtained in a small part of the chromatogram ( peak cluster ), in which three or fewer components contribute to the absorption [592]. 

First, the sample was examined by GPC, for which four columns of styragel of 106,10s, 104 and 103 A nominal pore size were used. The total number of theoretical plates as determined by acetone at a flow rate of 1 ml/min was ca. 26,000. The eluent was tetrahydrofuran. The chromatogram is shown in Figure 9, which indicates two peaks at ca. 21 and 24 counts. The former may be assigned to the tetra-chain, star-draped component, and the latter to the precursor. However, no complete separation of the two peaks was observed. For another comparison, velocity ultra-centrifugation was performed for the sample at 59,780 rpm using a 6-solvent for polystyrene, cyclohexane. The operation temperature was established at 35 °C, the 6-temperature, to minimize the concentration dependence of sedimentation velocity and other effects. A sedimentation pattern taken by UV-absorption is shown in Figure 10. It is seen that the separation of S-A sample into the two components was quite difficult even at a very low polymer concentration, 0.077 g/dl. 

Reduced ascorbic acid has its optical absorbance maximum at 245 to 270 nm depending strongly on pH. At pH 2, the absorption maximum is at 245 nm, and at pH 6.4 it is at 265 nm. Since fixed-wavelength 254-nm mercury lamp detectors are relatively inexpensive, 254-nm UV detectors are commonly used for ascorbic acid measurement. DHA absorbs at 210 to 227 nm, which limits the choice of the sample matrix, solvents, buffers, and other reagents used. Moreover, DHA degradation products may interfere with DHA in the chromatogram (12). Thus the direct UV detection of DHA is complicated, and usually DHA is reduced to ascorbic acid before chromatographic separation and measured as total ascorbic acid (43,66,81,82). 

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