# Plate Theory and Extensions - Quantitative Analysis from Retention Measurements > Page 50

From equation
(44), it is clear that when *only* (A) is present, the function will be at
a maximum when t = t_{A} and when *only* solute (B) is
present, it will be at a maximum when t = t_{B}. Thus, the composite
curve maxima will range from (t_{A}) and (t_{B}) for different
proportions of solutes (A) and (B). It is see that, from the value for the
retention time of the composite peak, the composition of the original mixture

can be
determined. For closely eluted peaks n_{A
}= n_{B} and _{} and
_{} are,
in effect, average dilution factors resulting from the peak dispersion and can
be replaced by a constant. The efficiencies (n_{(A)})
and (n_{(B)}) in the exponent
function, however, will only be equal if the peaks are *symmetrical*. This
is because the rear part of the first peak, merges with the front part of the
second peak. In LC, peaks are rarely symmetrical thus, (n_{(A)}) will represent the efficiency of the
rear half of the first peak (solute A) and (n_{(B)})
the efficiency of the front half of the second peak (solute B). In practice,
the efficiencies are calculated in the normal way except, twice the width
of the front half is used and twice the width of the rear half of the peak
instead of the total peak width. The extent to which (n_{(A)}) and (n_{(B)}) will differ will depend on the quality of the column
and the chromatographic system. Well-packed columns should give similar
efficiencies for the two halves of the peak but the front half is most often
slightly more efficient than the rear half of the peak. The response of the
detector to the specific solutes must also be taken into account. Thus, if (D)
is the voltage output from the detector, equation (44) can be put in the form