DETECTION AND IDENTIFICATION OF MOLECULAR WATER POLLUTANTS BY LASER RAMAN SPECTROSCOPY

Abstract

The Raman spectra of the potassium salt of 2,4-dichlorophenoxyacetic acid (24DK) in distilled water was determined from $180 cm^{-1}$ to $1600 cm^{-1}$, A 50 mW He-Ne gas laser (6328 {\AA}) with a multipass 2.5 ml Raman cell and Jarrell-Ash Model 25--300 laser Raman Spectrometer was used to detect the right-angle scattering. Four bands centered at approximately $400 cm^{-1}$, $800 cm^{-1}$, $1100 cm^{-1}$ and $1600 cm^{-1}$ are detectable at 500 ppm. The bands at $400 cm^{-1}$, $800 cm^{-1}$, $1100 cm^{-1}$ have small depolarization rates while the band at $1600 cm^{-1}$, which partly overlaps with the $1650 cm^{-1}$ Raman water band, has a relatively large depolarization ratio. The knowledge of these four bands and their depolarization ratios may serve as a means of detecting 24DK in water.