Normalization Method

The Normalization Method

The normalization method is the easiest and most straightforward and requires no reference standards or calibration solutions to be prepared. However, the detector must have the same response to all the components of the sample. In GC the response of the flame ionization detector (FID) depends largely on the carbon content of the solute. Thus, the technique can be used in GC when employing the FID sensing compounds of similar types (e.g. high molecular weight paraffins). An exceptional example in LC, where the normalization procedure is often used, is in the analysis of polymers by exclusion chromatography using the refractive index detector. The refractive index of a specific polymer is a constant for all polymers of that type having more than 6 monomer units so normalization is the obvious method to use. The method of calculation is simple but will depend on whether (r) is unity or not. Assuming, firstly, that (r) is unity, the percentage x(p)% of any specific polymer (p) in a given polymer mixture can be expressed by

(33)

where (ap) is the peak area of polymer (p)

or (34)

If peak heights are used, the percentage x(p)% of any specific polymer (p) in a given polymer mixture can be expressed by similar equations,

(35)

where (hp) is the peak area of polymer (p)

or (36)

However, assuming that (r?1) then equation (33) becomes,

(37)

equation (34 becomes,

(38)

equation (35) becomes,

(39)

and equation (36) becomes,

(40)

For the most part, contemporary computer chromatography software does not provide for situations where (r?1) so the analyst can only make the corrections manually. Alternatively, the chromatogram can be processed manually and peak areas used. The error involved from not correcting for (r) can only be accessed, if the actual value of (r) is known.