the width at half height or by calculating the area of a triangle formed by the baseline and the sides of
the peak produced to intersect above the maximum (Figure 4.28) i.e. 1/2 base × height. The methods are
simple and rapid but are unreliable if peaks are narrow or asymmetrical. Precision is only moderate.
Figure 4.28
Measurement of peak height and area.Cutting-out and Weighing
The peak is cut from the original chart paper or from a photocopy and weighed on an analytical balance.
This method is fairly precise and particularly useful for asymmetrical peaks but is subject to errors
arising from variation in thickness and moisture content of the paper.
Automatic Integration
Electronic integrators are the most rapid and precise means of determining peak areas. They have a
digital output derived by feeding the detector signal into a voltage-to-frequency converter which
produces a pulse rate proportional to the input signal. The total number of pulses is a measure of the
peak area and this can be printed out directly or stored until required. Electronic integrators have a wide
linear range, a high count rate and may automatically correct for baseline drift. In addition, the more
expensive versions will print retention data alongside peak areas. Computing integrators, based on a
microcomputer, are now widely available and are discussed in Chapter 13.
Calculation of Quantitative Results
Internal Normalization
If the components of a mixture are similar in chemical composition and if all are detected, the
percentage weight of each is given by