A Real Example

Although an excitation wavelength of 340 nm is quoted in the literature the module scan of orthophthalaldehyde, a derivative of the amino acid alanine, (Scan Orthophthalaldehyde Derivative of Alanine) shows a maximum between 220 nm and 240 nm.

Figure: Scan Orthophthalaldehyde Derivative of Alanine

When you are looking for the wavelength by scanning, scan over the whole range. As this example shows a maximum may be found in a completely different wavelength range.

NOTE

When comparing fluorescence excitation spectra directly with DAD spectra or literature based absorbance spectra, you should consider large differences in the used optical bandwidth (FLD = 20 nm) which cause a systematic wavelength maximum shift depending on the absorbance spectrum of the compound under evaluation.