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• Disregard limit: inject a solution of the substance to be examined at a concentration corresponding to the disregard limit (e.g. 0.05% of the concentration of the test solution) and note the area of the principal peak.

a) Disregard the peaks in the chromatogram obtained with the test solution having an area lower than or equal to this peak area. 

NB: instead of a solution of the substance to be examined at a concentration corresponding to the disregard limit, it is possible to use the reference solution used for the quantitation of the unspecified impurities (e.g. 0.10% of the concentration of the test solution) and to extrapolate the area of the principal peak to the disregard limit (e.g. half the peak area obtained with the reference solution at 0.1%).

b) For an impurity controlled using a solution of an impurity CRS, dilute the latter solution to the disregard limit. Report the impurity peak in the chromatogram obtained with the test solution if its area is greater than that of the principal peak in the chromatogram obtained with the diluted impurity CRS solution.

• Specified and unspecified impurities: compare the areas of the reported individual peaks with (x times) the area of the peak obtained with the reference solution, as stated in the monograph.

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• Disregard limit: inject a solution of the substance to be examined at a concentration corresponding to the disregard limit (e.g. 0.05% of the concentration of the test solution) and note the peak area of the principal peak.

a) Disregard the peaks in the chromatogram obtained with the test solution with an area lower than or equal to this peak area.

b) When an impurity requires a correction factor, report the impurity peak if its corrected area is greater than this peak area.

NB: instead of a solution of the substance to be examined at a concentration corresponding to the disregard limit, it is possible to use the reference solution used for the quantitation of the unspecified impurities (e.g. 0.10% of the concentration of the test solution) and to extrapolate the area of the principal peak to the disregard limit (e.g. half the peak area obtained with the reference solution at 0.10%)

• Specified and unspecified impurities: compare the (corrected) areas of the reported individual peaks with (x times) the area of the peak obtained with the relevant reference solution, as stated in the monograph.
• Total: sum up the areas of the reported individual peaks and compare the figure with (y times) the area of the peak obtained with the relevant reference solution, as stated in the monograph.

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