Absorption Spectroscopy of Biopolymers 朝陽科技大學吸收光谱的聚合物朝陽技大學.pptVIP

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Absorption Spectroscopy of Biopolymers 朝陽科技大學吸收光谱的聚合物朝陽技大學.ppt

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Absorption Spectroscopy of Biopolymers 朝陽科技大學吸收光谱的聚合物朝陽技大學

Absorption Spectroscopy of Biopolymers Experimental aspects Spectrum Analysis Solvents Solvent and Cuvette transparencies Spectral Bandwidth Chromophore absorptions Organic Chromophores Band Classification * UV-visible spectra are normally recorded on dilute solutions (10-6 to 10-3 M) of a sample and referenced to the pure solvent that the solute is dissolved in Solvents are normally chosen so that their absorption does not interfere with the solute peaks, as the UV-visible spectrometer has difficulty subtracting the signal of the pure solvent from the solvent in the sample solution The solvent end absorption or “solvent cut-off” may extend up to 250 nm for some solvents, so that peaks below below this wavelength must be regarded with some caution In addition, the material that the cuvettes (cells) are made of also absorb light in the UV region. Glass cells are opaque to the UV light up to 300 nm Quartz cells are transparent down to 170 nm Visible spectra may be obtained in cells of either material material opaque material transparent Harwood and Claridge, p. 14 Benzene hexane hexane 200 360 205 255 n ?__ ?s* n ?__ ?s* Methyl bromide Methyl Iodide C-X ? X=Br X=I ethanol ethanol 17 5,000 275 200 n ?__ ?p* p ?__ ?p* Nitromethane N=O hexane hexane 15 10,000 290 180 n ?__ ?p* p ?__ ?p* Ethanal C=O hexane 10,000 180 p ?__ ? p* 1-Hexyne C?C hexane 15,000 171 p ?__ ? p* Ethene C=C Solvent e lmax, nm Excitation Example Chromophore /~reusch/VirtualText/Spectrpy/UV-Vis/spectrum.htm 1.0 340 h to p* Azo (-N=N-) 1.0 271 h to p* Nitro (-NO2) 3.0 210 h to s* Thiol (-SH) 1.5 210 h to p* Amide (-C(=O)NH2) 1.5 205 h to p* Ester (-COOR) 1.5 205 h to p* Acid (-COOH) 3.5 190 h to s* Amine (-NR2) 1.0 290 h to p* 2.0 190 p to p* Aldehyde (–C(H)=O) 1.5 280 h to p* 3.0 180 p to p* Ketone (-C(R)=O) 3.5 180 h to s* Ether (ROR) 2.5 180 h to s* Alcohol (ROH) 3.0 175 p to p* Alkene (-C=C-) 3.0 170 p to p* Alkyne (-C≡C-) 1.0 160 h to p* Nitrile (-C≡N) log(