Interpretation of impurities

[Karan]

Hi everybody,

I have come across a difficult situation in interpreting the impurities in Timolol Eye Drops.

As per BP monograph:
In the chromatogram obtained with solution (2) the area of any secondary peak , other than the peak corresponding to maleic acid, is not greater than the area of the peak obtained with solution (1) (0.4%) and not more than two such peaks have an area greater than that of the peak obtained with solution (3) (0.2%).

Does it mean:

Highest unknown impurity: Not more than 0.4%

Sum of any other two highest impurities (excluding highest unknown impurity of 0.4%): Note more than 0.2%


If not what is the correct interpretation?

rgds.

[grzesiek]

you can have only two peaks that can be bigger than 0.2% (but not bigger than 0.4%)

so posiibilities are for example
peak1 - 0.39%, peak2 - 0.38% and since you already have two peaks bigger than 0.2% each, other peaks must be smaller tahn 0.2% let's say 0.19%