An instrument that meets the EPA's minimum requirements shall have filter combinations to measure fluorescence at 2 different portions of a CDOM Excitation Emission Matrix. This means there should be no overlap of emission wavelengths, including filter bandpasses.
An example :
emission filter 1 = 420 nm +/- 20 nm bandpass
emission filter 2 = 470 nm +/- 20 nm bandpass
The excitation filters shall be selected between Exc = 300-370 nm, where, either one or two different wavelengths could be chosen. Two combination examples could be:
(1) Ex/Em 1 = 350 / 420 nm; Ex/Em 2 = 370 / 470 nm
(2) Ex/Em 1 = 350 / 420 nm; Ex/Em 2 = 350 / 470 mn
The choice of filters, in conjunction with lamp and detector design of a specific manufacturer should be based on optimizing CDOM fluorescence detection in natural waters.