Investigation Of Seawater Anions' Aqueous Solutions By Laser Raman Spectrometry

The investigation of hydrothermal vents is the top topic of the marine geology study recently. Laser Raman Spectrometry (LRS) is a proven and powerful technique in geochemical analyses. Furthermore, it is a rapid, repeatable, and especially nondestructive technique which used to investigate marine objects. The acquisition of spectra in-situ is in the primary stage currently in American and European countries, and no relative domestic reports has been published. This thesis are dealing with the investigation of seawater and seawater anions' aqueous solutions by LRS, analyzing Raman properties of seawater and seawater anions' aqueous solutions under the conditions of room temperature and temperature changing. Using Gaussian Fit method to data processing, improve identifiable and analytical precision.This thesis uses Laser Raman spectroscopic system to investigate the spectra of seawater and sodium sulfate, sodium carbonate, sodium bicarbonate aqueous solutions of different established concentrations. Example spectra of aqueous solutions show sulfate and carbonate have strong band centered at -981cm^-1and -1066cm^-1, respectively, which both due to the symmetric stretching mode(v₁). And bicarbonate has two band, -1016cm^-1 and -1364cm^-1, which due to stretching mode(v₅) and symmetric stretching mode(v₁). The results show that anions' relation curves between ratios of intensity and salinity are quite well in linear relation in single solutions, but relation curves of carbonate and bicarbonate in mixed solutions are not as well as in single solutions due to the dissociation of bicarbonate to form carbonate, which cause the amount changing. Calculates the relative cross-section ratios (?)and (?) with Gaussian fit results which were 2.52(±0.1) and3.88(±0.01), respectively. Combining the concentrations in seawater and the relative cross-section ratios, concludes the relative Raman intensity of sulfate, bicarbonate, carbonate in seawater is 28:0.5:0.08. The spectrum of seawater near Qingdao sea area shows a Raman-active band of sulfate centered at -981cm^-1, neither carbonate's nor bicarbonate's signal could be observed. And a strong fluorescence of seawater interfered with Raman signal is found in this range, which might be caused by the chromophoric dissolvable organic matter (Yellow Substance) and chlorophyll in seawater. Subsequently, this thesis detects spectra of sodium sulfate, sodium carbonate and sodium bicarbonate solutions under a series of temperature, and finds Raman shifts of anions are moving toward low wave number while temperature increasing. It indicates the length of covalent bond in anions augments which cause the energy of bond minishes. The oxyhydrogen bonds are moving toward high wave number while temperature increasing and the intensities ratio between two fit peaks changes, which indicate the hydrogen bond effect is weakening.