Measurement of permanganate Index in water using hand-held fluorescence spectrometer

Fluorescence spectroscopy has received attention in the water quality monitoring, as it is a rapid, reagentless technique that requires no sample preparation prior to analysis. It has been investigated as a monitoring tool for a range of applications including water quality and pollution monitoring in marine, rivers and lakes. The permanganate index (CODmn) can reflect the degree of water damage by organic pollutants, and is an important indicator for water environment protection and marine monitoring. In this paper, we present a compact handheld fluorescence spectrometer for water CODmn measurement. The semiconductor laser, spectroscopic unit and detection unit are integrated in the spectrometer, its actual size is about 100mmx60mmx25mm. The spectrometer covers the wavelength range of 400-760 nm, with spectral resolution of 2 nm. The semiconductor laser emitting at 405 nm is employed as the excitation source, which is controlled by the computer. The laser is incident into the water in test bottle at a certain angle in order to avoid the interference come from the bottle wall. The scattered light, water Raman light and organic matter fluorescence excited by the laser can be received by the spectrometer. The CODmn can be obtained according to the method of intensity ratio of laser Fluorescence-Raman signal proposed by us. In the experiment, water samples collected from 9 different sites of Sow River at Weihai are tested by using our designed handheld fluorescence spectrometer. The CODmn can be achieved by the computer analyzing the spectral curve. In addition, we also measured the 9 water samples by chemical method, and the obtained permanganate index compared very well to the values by using our designed spectrometer: a significant relationship (R-2=0.941) is identified between the two methods. The experimental results indicate that our designed spectrometer has the advantages of small size, high sensitivity and high detection speed, which is promising for CODmn monitoring in many water areas.