Advanced Materials Research Online: 2014-06-18 ISSN: 1662-8985, Vols. 955-959, pp 1376-1379 doi:10.4028/www.scientific.net/amr.955-959.1376 2014 Trans Tech Publications, Switzerland The Linear Relationship between Concentrations and UV Absorbance of Nitrobenzene Dan Wu a, Kaixiao Zhang b College of Science, Hohai University, Nanjing, China a 18251828552@163.com, b KXZhang@hhu.edu.cn Keywords: Nitrobenzene, UV Absorbance, Absorption Peak, Integration of Absorbance Abstract. This paper researched the linear relationship between UV absorbance and concentrations of nitrobenzene. It used the UV-1700 UV/VIS spectroscopy to get the absorbance diagram and analyze it. Then it calculated the absorbance of maximum absorption peak and the absorbance integration in a wavelength interval. There is a linear relationship between absorbance and concentration, the correlation coefficient is 0.981 of the maximum absorption peaks and the concentrations, and the largest correlation coefficient between concentrations and the integration of absorbance is 0.995 with the wavelength interval of 235-245 nm, which is between the two absorption peaks of 210 nm and 270 nm. Therefore, it s a good way to use integration of absorbance in the middle of two absorption peaks to measure the concentration of nitrobenzene, which is more accurate and reliable. Introduction In recent years, environmental pollution incidents occurred frequently in China, including increasing water pollution. And among different kinds of water pollution, organic pollution is the most serious and harmful [1].How to accurately analyze the types and concentrations of organic pollutants has been crunch time. Nowadays the traditional physical and chemical methods and the emerging spectrum detection method are the mainly two types of methods in the field of organic pollution index of water quality on-line monitoring device [2]. By comparison, spectrum detection method has a fast detection speed, no chemical reagent two pollutions, simple operation and maintenance, low operating cost and other benefits. It is very suitable for online detection of water quality. Especially the detector UV (ultraviolet) absorbance analysis based on not only the hair, portable, as well as online is more convenient and effective. Nitrobenzene is a highly toxic organic compound, which is insoluble in water. It is usually used as oxide and mild organic solvents. It is mainly used in the manufacture of aniline dyes, and also used as insulating material and gloss agent [3]. The nitrobenzene of environment mainly comes from waste water and gas, the chemical plant, dye plants. A large number of nitrobenzene also can be found in aniline dye factory sewage. Accidents in the process of storage, as well as will cause serious pollution of nitrobenzene. Theory The experiment used UV spectral data to measure organic pollutant concentration in water. It based on the characteristic absorption spectrum measurement of organic substances containing an unsaturated bond [4]. So we could establish the mathematical model of spectral data and concentrations of organic contaminants according to the abundant spectral information in the ultraviolet spectral region. With the extrapolation capability of the model, we could forecast organic pollutants concentration of unknown samples spectra in water. Therefore, the key technology of UV spectrum analyzer was the establishment of mathematical model and the extrapolation ability of the model. Absorbance refers to the base 10 logarithm of light s incident intensity and transmitted intensity through solution or substances. It is affected by solvent, concentration, temperature and so on. The absorbance is denoted by A and is a physical quantity to measure the degree of light absorbed by material. Absorbance of different organic pollutants is different. In this experiment, we got the data of different concentrations of nitrobenzene solution through the UV detection. Next we used Origin software to draw the original spectra, and reached the absorbance by using the absorbance of All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 130.203.136.75, Pennsylvania State University, University Park, USA-13/05/16,00:33:30)
A a.u. Advanced Materials Research Vols. 955-959 1377 the definition of LG (Iin/Iout) and the measured data. Then, we used MATLAB and SPSS software to undertake data processing by linear regression and correlation analysis methods. Finally we obtained the relationship between absorbance and the wavelength and absorbance and concentration. And then we applied the conclusion in practice, judging the types of organic pollutant according to concentration and absorbance. Experiments The agents of this experiment are distilled water and nitrobenzene of 98-95-3 types. They were mixed in different proportions to makes different concentration of nitrobenzene solutions. Then the UV-1700 type ultraviolet visible spectrophotometer was used to measure the solutions and obtain experimental data. We obtained 11 parts of tap water of 200ml,and place them in a vessel in turn, and number them from 0 to 10. Nitrobenzene of 0µl, 0.1µl, 0.5µl, 5µl, 10µl, 20µl, 30µl, 40µl, 50µl, 60µl, 70µl, were added to the 11 parts of water and mixed evenly, Then obtained 11 kinds concentration of nitrobenzene solution. 11 parts of nitrobenzene were treated with UV-Vis spectrophotometer to get the original spectrum. And according to the definition of original spectra and absorbance, we obtained absorbance diagram. Discussion 6000 5000 4000 3000 2000 5ppm 1000 0 150 200 250 300 350 400 450 (nm) Fig.1 The UV spectra of 5ppm nitrobenzene solution 2.5 2.0 1.5 1.0 0.5 0 0.1ppm 0.5ppm 2.5ppm 5ppm 10ppm 15ppm 20ppm 25ppm 30ppm 35ppm 0.0-0.5 150 200 250 300 350 400 450 (nm) Fig.2 The absorbance graph solution of different concentrations of nitrobenzene Taking the nitrobenzene solution of 5 ppm as an example, it used the UV/VIS spectrophotometer to measure it, and got the original spectra. The picture was shown in Figure 1. We measured 11 different concentrations of nitrobenzene solutions by the UV/Vis spectrophotometer, and got the original spectra. Then we got the absorbance graph by calculation. Figure 2 showed the concentration of nitrobenzene solution of all absorbance graphs. We found 2 absorption peaks in the vicinity of 210nm and 270nm from Figure 2. When the concentration of nitrobenzene is between 0-5ppm, the maximum absorption peak is in the vicinity of 210nm. When the concentration of nitrobenzene is between 10-35
1378 Advances in Environmental Technologies III ppm, the maximum absorption peak is in the vicinity of 270 nm. We calculated the maximum absorption peak of each concentration of nitrobenzene solution, and then got 11 sets of three-dimensional array composed of concentration, wavelength and the maximum absorption peak, as shown in Table 1. Table 1 The UV absorbance of maximum absorption peaks data Concentration (ppm) 0 0.1 0.5 2.5 5 10 15 20 25 30 35 Wavelength (nm) 210.15 210.75 206.77 211.35 210.75 269.07 67.8 267.45 268.29 269.91 272.85 Absorbance (Abs) 0.557 0.644 0.628 0.635 0.691 0.948 1.355 1.619 1.760 1.875 1.895 Table 2 The relationship between the integration of absorbance and concentration Concentration (ppm) 0 0.1 0.5 2.5 5 10 15 20 25 30 35 Integration of absorbance (Abs) 5.63080 6.26330 6.73200 6.22900 7.23600 10.3664 13.2086 15.4245 16.8124 18.9566 19.9581 Fig. 3 The fitting linear graph of concentration and absorbance Fig. 4 The fitting linear graph of the integration of absorbance and concentration We used the concentration and absorbance to do correlation analysis [5], and then got the correlation coefficient of absorption peak and the fitting linear graph. It was shown in Fig. 3. From Fig. 3, we found that the absorption peak and concentration are close to a linear relation in 0-30ppm. The correlation coefficient is 0.981. There is a good correlation between them. After the 30ppm, they do not constitute a linear relationship. Similar to the above, we obtained 11 absorbance diagrams of different concentrations of nitrobenzene solution by UV visible spectrophotometer. We selected a wavelength interval of 220-260nm between two absorption peak, integrated the absorbance in the
Advanced Materials Research Vols. 955-959 1379 interval, and obtained a two-dimensional table of absorbance integral value and the concentration, as shown in Table 2. We did the correlation analysis of the integration of absorbance and concentration. The correlation coefficient is 0.992. Fig. 4 shows the correlation analysis and the fitting linear graph of for the absorbance the integration of absorbance and concentration at the wavelength of 220-260nm integral value. Table 3 The correlation coefficients of the integration of absorbance and concentration in multiple wavelength intervals wavelength intervals (nm) 200-220 200-240 205-215 210-270 215-265 220-260 correlation coefficients 0.887 0.987 0.860 0.981 0.985 0.992 Wavelength intervals (nm) 225-255 230-250 235-245 240-280 260-280 265-275 correlation coefficients 0.992 0.994 0.995 0.976 0.966 0.963 In order to get the relationship of the integration of absorbance and concentration, this experiment chose several wavelength intervals near two absorption peaks and between them, and then integrated the absorbance in the intervals. We calculated the correlation coefficients of multiple wavelength intervals by using SPSS software, as shown in Table 3. Correlation coefficients near two absorption peaks of absorption concentration are less than between them. Therefore, if we want to determine nitrobenzene concentration through the determination of the integration of absorbance, we should choose appropriate wavelength intervals between two absorption peaks. Conclusions The experiment was to measure the maximum absorption peak and the integration of absorbance in a wavelength interval. And then we respectively connected them with the concentration of nitrobenzene by correlation analysis. The correlation coefficient of the absorption peak and concentration is 0.981. While the relativity of the integration of absorbance and the concentration in a wavelength interval varies with the wavelength interval. The relativity is high of the appropriate wavelength interval between two absorption peaks. For example, the correlation coefficient is 0.995 of the integration of absorbance in 235-245nm and concentration. Therefore, we can use the integration of absorbance in a proper wavelength interval to measure the concentration of nitrobenzene solution. And this way is more accurate and reliable by comparison. Acknowledgements Financial support from Students Innovation Training of China is acknowledged. The authors would like to give her thanks to the Innovation Foundation of HoHai University. References [1] Wu Tonghua, Guo Hong, Guo Jingci. Environmental Monitoring in China. 2009, 25(4):57 [2] Deflandre B.,Gagne J.-P..Estimation of dissolved organic carbon (DOC) concentrations in nanoliter samples using UV spectroscopy. Water Pesearch.,2001, 35 (13):3057-3062 [3] Du Shuxin,Wu Xiaoli,Wu Tiejun. Chinese Journal of Analytical Chemistry,2004,32(9):1227 [4] Liu Sidong,Cui Xiujun,Zhang Zhuoyong,et al. Spectroscopy and Spectral Analysis,2003, 23(1):119 [5] Rao C.R.,Toutenburg H.Linear models[m].new York:Springer Verlag Press.1995
Advances in Environmental Technologies III 10.4028/www.scientific.net/AMR.955-959 The Linear Relationship between Concentrations and UV Absorbance of Nitrobenzene 10.4028/www.scientific.net/AMR.955-959.1376