uv_visible_spectroscopy：uv_visible_spectroscopy.ppt

The first step is to close a shutter in the path (or adjust dark filter) and adjust 0 %T. The second step is to open the shutter and place the cell containing only the solvent in the light beam and adjust the scale on 100 % T (equivalent to 0 absorbance). The third step is to place the sample cell in the light path and measure the intensity IT or its equivalent absorbance. In double beam spectrophotometer, the monochromatic light is split by the beam splitter in to two equal intensity light beam, which are directed alternatively in rapid succession through a cell containing the sample and one containing the solvent only. This instrument measures the ratio of the intensity of the beam coming through the sample and through the solvent. Changes in the intensity of the source affect both beams proportionately so the ratio of their intensities is not altered. Therefore, a high degree of stability in the light source is not required in these instruments. Difference in the lamp out put, optical system throughput, and detector sensitivity with wavelength also affect both beams in the same way. APPLICATIONS:1. Qualitative Analysis:  The UV spectra of most compounds are of limited value for qualitative analysis as compared to IR and Mass spectra. Qualitative analytical use of UV spectra has largely involved λ-max and absorptivities, occasionally includes absorption minima. In pharmacopoeias, absorption ratios have found use in identity tests, and are referred to as Q-values in USP. 2. Quantitative Analysis:  UV spectroscopy is perhaps the most widely used spectroscopic techniques for the quantitative analysis of chemical substances as pure materials and as components of dosage forms.  A)??? Single component Analysis:  Direct Analysis: Essentially all compounds containing conjugated double bond or aromatic rings, and many inorganic species absorb light in the UV-visible regions. In these techniques the substance to be determined is dissolved in suitable solvent