Abstract
Though the Methylene Blue colorimetric method has been widely used for the determination of the concentration of alkylbenzenesulfonate (ABS) in the polluted waters, this method does not always give a corret result because there exist in the waters some materials, other than ABS, which react with Methylene Blue and affect the analytical value of ABS. The result of the analysis, therefore, is often represented as the concentration of Methylene Blue active substances (MBAS).
On the other hand, the infrared spectral method is considered to give a more precise value for the analysis of ABS. However, infrared spectral method. of methylhepthylamine complex of ABS is too complicated and needs too much time to be a practical use.
The authors attempted to determine the concentration of ABS in the polluted waters more readily combining the Methylene Blue colorimetric method with infrared spectrometry as follows:
(1) The complex of Methylene Blue active substances and Methylene Blue (MBAS-MB) was extracted from the water with an organic solvent (1, 2dichloroethane) in a similar way as conventional methods. From the measurement of the absorbance at the wavelength 655 mμ of the solution the concentration of MBAS in the water was determined.
(2) After the solvent of the solution of MBAS-MB complex was evaporated up, the residue was prepared for the infrared spectrometry.
The absorbance peaks of the infrared spectrum of the MBAS-MB complex at the wavenumber 890 cua-1 and at 1010 cm-1 were characteristic for Methylene Blue and ABS respectively. It was found that the ratio of the peak height at the wavenumber 1010 cm-1 Y, to the peak height at 890 cm-1, X, of the spectrum was proportional to the ratio of ABS to MBAS in the complex. A calibration curve was constructed for the relation between Y/X and ABS/MBAS by standard solutions. Thus using this calibration curve, the ratio ABS/MBAS in the water was estimated by an infrared spectrum of MBAS-MB complex. Multiplying MBAS concentration given in the procedure (1) by ABS/MBAS, we could estimate the net content of ABS in the water.
The reproducibility and recovery test of this method showed fairly good results. As more than about 0.5 mg of MBAS-MB complex is necessary for the infrared spectrometry, this method is not applicable for the analysis of the water with very low concentration of MBAS. It is, however, considered to be very useful for the analysis of highly contaminated waters or bottom sediments which contain a lot of Methylene Blue active substances other than ABS.
