Dissolution of losartan potassium tablet

I am perform dissolution test for Losartan potassium as method in USP with water as dissolution medium with maximum wavelength at 256 nm. But when I scan both standard or test preparation with water as blank I received no maximum absorption wavelength at 256 nm as USP. Anyone help me explain why

Losartan may not have a good peak anyway. The USP recommended wavelength 256nm could be one of many wavelengths you can use for this test. The selection of 256nm in USP may be given by the sponsor of monograph and the sponsor may have various reason for selecting that wavelength. It is safe to follow USP method unless you want to justify changes and fully validate your new conditions. Anyway where did you find maximum for losartan standard and test preparation with water as blank? Did you find a better wavelength for this test?

you may use modified or other method since validated.
if you feel that other wavelength has better sensitivity, you may validate your method and if it is valid you can use it.