Error, from close eluting peaks

In fact, there is no reason why a detector should not have a logarithmic, exponential or any other functional output as long as the function can be explicitly defined. However, chromatograms obtained from such detectors would be unfamiliar and difficult to interpret and calculations for quantitative analysis would become very involved. The concentration profile of an eluted peak closely resembles that of the Gaussian or Error function where the independent variable is the volume of mobile phase passed through the column and the dependent variable solute concentration in the mobile phase. If the flow rate through the chromatographic system is constant, then the independent... 

Some of the factors mentioned earlier which introduce error when calibrating with external standards only, can be compensated for by introducing a constant amount of an internal standard in both the unknown and the standard calibration samples. This should be a compound with similar chemical nature to the analytes, so that it will pass through the sample extraction and preparation procedure similarly. In general it should elute in the chromatographic system close to the other peaks in the system, but separated from all of them, so it can be identified and measured accurately. One calculates the ratio of the peaks responses to their concentrations. Then the ratio for each analyte. A, peak is compared to ratio of the internal standard, IS peak, to give the relative response factor (RRF), for the analyte to... 

In order to optimize a separation and produce it in the minimum time, the capacity ratios and separation ratios must be measured for a given pair of enantiomers under known conditions of mobile phase composition and temperature (this will be discussed in detail later in this chapter). Unfortunately, when two peaks are eluted close together, which frequently occurs in chiral chromatography, the positions of the peak maxima are distorted due to the immediate presence of the other peak. An example of this problem is shown in figure 10.1, where the peaks are simulated and added, and the composite envelope plotted over the envelope of each individual peak. It is seen that the actual retention difference, if taken from the maxima of the envelope, will give a value of less than 60% of the true retention difference. Unfortunately, this type of error will probably not be taken into account by most data processing software. It follows, that if such data is used in an attempt to calculate the... 

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