Determination of trace phenols in wastewater by ultraviolet difference spectroscopy experiment
Determination of trace phenols in wastewater by ultraviolet difference spectroscopy experiment
This experiment is from the official website of College of Chemistry, Qingdao University of Science and Technology.
Operation method
Determination of trace phenols in wastewater by ultraviolet difference spectroscopy experiment
Principle
Phenol has two absorption peaks in the ultraviolet region, λmax is 210nm and 270nm in neutral solution, in alkaline solution, due to the formation of phenol salts, and the absorption peaks are red shifted to 235nm and 288nm. The so-called difference spectrum is the spectral curve obtained by subtracting these two absorption spectra. In the experiment, as long as the alkaline solution of phenol is put on the sample optical path, and the neutral solution is put on the reference optical path, the difference spectrum can be plotted directly. On the differential spectral plot of phenol, 288 nm was chosen as the measurement wavelength, at which the absorbance of the solution had a good linear relationship with the change of phenol concentration, following Beale's law, i.e., ΔA=Δε?C?L, which can be used for quantitative analysis of phenol. Difference spectrometry for quantitative analysis can eliminate the interference of some impurities in the sample, simplify the analysis process, and realize the direct determination of trace phenol in wastewater.
Materials and Instruments
KOH solution Phenol standard solution Move 1. Determination of wavelength: Using distilled water as reference, the absorption curves of phenol in neutral and alkaline solutions are plotted. Then, the neutral and alkaline solutions of phenol are placed in the reference and sample optical paths, and the difference spectral curves of the two are plotted, and the wavelength is determined according to the difference spectral curve. Caveat 1. Plot the absorbance-concentration curve and calculate the regression equation using the difference in absorbance measured in step 2. 2. Calculate the phenol content (mg/L) in the water sample using the absorbance-concentration curve or the regression equation. For more product details, please visit Aladdin Scientific website.
WFZ-26A UV-visible spectrophotometer 1cm thick quartz colorimetric absorption cell 25ml volumetric flasks
2. Plotting the standard curve: Pipette 1.0 ml, 1.5 ml, 2.0 ml, 2.5 ml, 3.0 ml of phenol standard solution into five 25 ml volumetric flasks, and take the same volume of phenol standard solution into another five 25 ml volumetric flasks, and dilute them with water and 0.1 M KOH to the scale respectively (a total of 10 25 ml volumetric flasks are needed). The concentration of each pair of volumetric flasks is 10mg/L, 15mg/L, 20mg/L, 25mg/L, 30mg/L. Each pair of phenol standard solution contains the same concentration of phenol, only the dilution solvent is different. At the measurement wavelength, the standard solution diluted with alkaline solution was placed on the sample optical path and the standard solution diluted with neutral solution was placed on the reference optical path, and the absorbance difference was measured.
3. Measure the phenol content in the unknown sample: Pipette 10 ml of phenol-containing water samples into two 25 ml volumetric flasks and dilute them with water and 0.1 M KOH to the scale. At the measurement wavelength, put the sample to be tested diluted in alkaline solution on the sample optical path, put the sample to be tested diluted in neutral solution on the reference optical path, and determine the difference in absorbance.