Improved purity assessment of high-performance liquid chromatography diode array detection data for overcoming the presence of the non-linearity artefact

Orthogonal projection approach (OPA) and needle search (NS) have been applied to assess the purity of peaks in a spectrochromatogram recorded with a high-performance liquid chromatograph coupled with a diode array detector. The background disturbances result in a non-linearity artefact at low concentrations and give an additional variation in the data set, which is difficult to correct due to the small magnitude of the baseline anomalies. The presence of non-linearities leads to artefact peaks in both OPA and NS plots. Decision criteria and certain modifications were introduced in OPA and NS in order to obtain more informative results and to distinguish artefact peaks from peaks corresponding to minor components. Small positive offsets were included in NS and a threshold curve obtained from the standard of the main compound was introduced in OPA. Both methods perform equally well for the detection of the impurities in the presence of non-linearities. Although, OPA requires a certified standard and additional experimental work.