The reason you got the mAu is because it is the "absorbance unit" on the "UV" detector. You will have "0" mAu for something that does not absorb the light at the setting wavelength. For instance, if you put water in the cell and look at the 254 nm and assume that water does not absorb light at this wavelength, the reading will be 0 mAu. If you have acetone which will absorb the light to the max, you will get the reading at the maximum absorbance full scale (normally 2 Au or 2000 mAu. On the other hand, fluorescence detector is the detector that measure amount of light (emission wavelength)  that the compound emit when it was subjected the light at a lower wavelength (excitation wavelength). It light intensity reacts with the detector and give an electrical signal and you measure in mV.  Bottom line, it does not matter what the unit is, All you need is to plot an  xy graph between the concentration of analyte (x) and the detector signal (y) in mAu or mV to make a calibration curve so you can estimate the amount of the unknown.

The reason you got the mAu is because it is the "absorbance unit" on the "UV" detector. You will have "0" mAu for something that does not absorb the light at the setting wavelength. For instance, if you put water in the cell and look at the 254 nm and assume that water does not absorb light at this wavelength, the reading will be 0 mAu. If you have acetone which will absorb the light to the max, you will get the reading at the maximum absorbance full scale (normally 2 Au or 2000 mAu. On the other hand, fluorescence detector is the detector that measure amount of light (emission wavelength)  that the compound emit when it was subjected the light at a lower wavelength (excitation wavelength). It light intensity reacts with the detector and give an electrical signal and you measure in mV.  Bottom line, it does not matter what the unit is, All you need is to plot an  xy graph between the concentration of analyte (x) and the detector signal (y) in mAu or mV to make a calibration curve so you can estimate the amount of the unknown.

As always in instrumental analysis: by calibration with a known compound? If you have a compound of known absorption and fluorescence coefficient at a defined wavelength, know its concentrationand the effective pathlength and irradiated area, you should be able to do the maths yourself?

Unfortunitely it seems you should still use mVolts for FLD is not an absorbance detector.

Dear colleague,

I agree with Narong Chamkasem .

meaning of AU is arbitrary  unit. based on the  type of detector , this unit is different.

Thanks All for your valuable and scientific discussion. it was really helpful.