Peak height,factors influencing

El Fallah, M.Z., Martin, M. (1987). Influence of the peak height distribution on separation performances discrimination factor and effective peak capacity. Chromatographia 24, 115. 

Example The influence of relative slit width on peak shape and resolution is demonstrated on the second isotopic peak of toluene molecular ion, m/z 94 (Fig. 4.25). With the entrance slit at 50 pm and the exit slit at 500 pm the peak is flat-topped (left), because a narrow beam from the entrance sweeps over the wide open detector slit keeping the intensity constant as the scan proceeds until the beam passes over the other edge of the slit. Closing the exit slit to 100 pm increases resolution to 2000 without affecting the peak height (middle), but reduces the peak area by a factor of 4 in accordance with an increase in resolution by the same factor. Further reduction of the exit slit width to 30 pm improves... 

There are a variety of other factors that influence the accuracy of quantitative analysis. Noise, in the form of baseline disturbances and baseline drift, affects area more than it does height, as it can cause area to be lost at the tailing edges of the peaks where they are widest. Peak asymmetry and detector saturation or nonlinearity, however, have a more detrimental effect on peak height. Figure 7.6 shows a calibration curve comparing peak height measurements with peak area measurements.13... 

Gas chromatographic peaks can be influenced by a variety of instrumental factors. We can often compensate for variations in these factors by using the internal standard method. Here, we add the same amount of internal standard to mixtures containing known amounts of the analyte and to the samples of unknown analyte concentration. We then calculate the ratio of peak height (or area) for the analyte to that of the internal standard. 

Quantitative analysis using the internal standard method. The height and area of chromatographic peaks are affected not only by the amount of sample but also by fluctuations of the carrier gas flow rate, the column and detector temperatures, etc., i.e. by variations of those factors which influence the sensitivity and response of the detector. The effect of such variations can be eliminated by use of the internal standard method in which a known amount of a reference substance is added to the sample to be analysed before injection into the column. The requirements for an effective internal standard (Section 4.5) may be summarised as follows ... 

The plate theory does not consider the effects of the carrier gas flow rate and the rate of mass transfer on the peak width, so that it says nothing about the factors which influence the equivalent height of a theoretical plate. According to plate theory, H decreases continuously with increase of flow rate, as distinct from experimental results which reveal a minimum at a certain flow rate. 

Band spreading is also related to an obstructive factor that is not a constant in a column bed. Both Kubin [6] and Pfannkoch et al. [11] have shown that plate height varies as a function of K. It appears that as its molecular size approaches the pore dimensions, a solute experiences diffusion limitations, decreasing its effective diffusion coefficient. This influence of restricted molecular movement on plate height (//) can be readily observed in SEC profiles. The first peak to elute after the void volume marker is frequently the broadest peak in the chromatogram. If one were able to obtain columns with different pore diameters but similar plate counts, pore volumes, and calibration curve slopes, it would be best to select a column on which would be 0.2 or greater for the solutes to minimize the effect of the obstructive factor. 

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