Excitation-Emission Matrix Scanning Spectrofluorometer

A compact rapid-scanning spectrofluorometer specifically designed to acquire an excitation-emission matrix (EEM) has been developed. A conventional grating monochromator is used for selecting the excitation wavelength. The induced fluorescence is monitored with the use of a variable circular interference filter. The EEM is acquired through rapid scanning of the fluorescent wavelength achieved via rotation of the filter in conjunction with slow scanning of the excitation wavelength using a computer. A Xe-arc lamp modulated at 540 Hz is used as an excitation source. The fluorescent signal is then detected by a photomultiplier tube whose output is integrated by a lock-in amplifier. The excitation flux is simultaneously monitored with the use of a quantum counter to compensate for the fluctuation of the lamp intensity. A 26 × 31 element EEM can be acquired within a minimum time of 4 min at a detection limit of 2 μg/L with the use of fluoresceine in ethanol as sample. The performance of our EEM scanning spectrofluorometer is further evaluated for other samples of different components.