Rw. Andrews et H. Richardson, EFFECT OF SPECTRAL RESOLUTION, DETECTOR LINEARITY AND CHROMATOGRAPHICRESOLUTION ON PEAK PURITY CALCULATIONS, Journal of chromatography, 683(1), 1994, pp. 3-8
The detection of inhomogeneity in chromatographic peaks is one of the
principal benefits of photodiode array detection for HPLC. The peak ho
mogeneity can be estimated by comparing the angles between the vector
representations of the instantaneous spectrum and the peak apex spectr
um, and the instantaneous spectrum and the spectral noise. When the sp
ectral or purity angle exceeds the noise angle, the peak is not homoge
neous because the differences between the instantaneous spectra and th
e apex spectrum cannot be explained by statistical variation of the ap
ex spectrum. In this paper, we consider the impact of detector lineari
ty and slit width on the purity (homogeneity) measurements of a separa
tion of a series of compounds related to vanillin. The peak purity ang
le, i.e., the spectral contrast of spectra within a chromatographic pe
ak, varies with the maximum absorbance. At small maximum absorbances (
less than 0.1 AU), the variation in purity angle is dominated by syste
m noise. At large maximum absorbances (greater than 0.5 AU), the varia
tion in purity angle is dominated by the photometric uncertainty. The
smallest measurable purity angle for a homogeneous peak is inversely p
roportional to the slit width and spectral bandpass of the polychromet
er of the photodiode array detector.