Ultraviolet spectrophotometric method for the determination of the purity of substances - Determination of trace benzene in ethanol - Database & Sql Blog Articles

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Determination of Purity of Substance by Ultraviolet Spectrophotometry-Determination of Trace Benzene in Ethanol

Key words: ultraviolet spectrophotometry; trace benzene in ethanol; aesthetic analyzer ; UV-1100

Width="1412" height="457" src="http://i.bosscdn.com/blog/nophoto.gif" /></p> First, the purpose of the experiment: 1, learning to use UV-visible spectrophotometer to check Principles and methods of material purity. 2. Skilled operation of the UV-Vis spectrophotometer. III. Experimental Principle Ultraviolet absorption spectroscopy is a commonly used method in organic analysis. It has the characteristics of simple equipment, convenient operation and high sensitivity. It has been widely used in the qualitative, quantitative and structural identification of organic compounds. Since the absorption peak of the ultraviolet absorption spectrum is usually wide and the number of peaks is small, it is not very specific in structural analysis. Generally, the type of the conjugated system is judged based on the position and intensity of the maximum absorption peak, and in the case of similar structure, the isomers having different conjugate modes are distinguished. Conjugated double bond compounds with π electrons, aromatic compounds, etc., have strong absorption in the ultraviolet spectral region, and their molar absorptivity ε can reach 10<sup>4</sup>-10<sup>5</sup> On the order of magnitude, this is significantly different from saturated hydrocarbon compounds. By utilizing this property, it is possible to easily check whether a pure saturated hydrocarbon compound contains a compound impurity such as a conjugated double bond or an aromatic compound. For example, in ethanol and cyclohexane, there is a trace impurity benzene. Since benzene has a B absorption band, the absorption wavelength is in the range of 230 to 280 nm, and ethanol and cyclohexane have no obvious absorption peaks here. Therefore, according to the fine structure absorption band of benzene at 230~280 nm, it can be judged whether there is trace impurity benzene in ethanol or cyclohexane. Third, instruments and reagents to analyze UV-1100 UV-visible spectrophotometer; quartz absorption tank with cover, 10mL volumetric flask, 5μL micro-injector; benzene, absolute ethanol. IV. Experimental contents and steps 1. Preparation of the solution Use a micro-syringe to remove about 2 μL of pure benzene in a 10 mL volumetric flask, dilute to the mark with absolute ethanol, and shake well. 2. Determination of absolute ethanol a. Turn on the ultraviolet instrument and preheat for 20 minutes. b. In the colorimetric tank, put "black body", "empty colorimetric dish (with air as reference)", "anhydrous ethanol". c. Select a wavelength, place the “black body” on the optical path, press “MODE” to “T”, press “0%” to display “000”. d. Pull “empty cuvette” to the optical path, press “100%”, display “100.0”, press MODE to “ABS”. e. Pull the sample to the optical path. The displayed value is the absorbance of absolute ethanol at this wavelength. f. Repeat the c-e three steps for each wavelength measurement. (Test wavelengths are: 230 nm, 240 nm, 245 nm, 250 nm, 252 nm, 253 nm, 254 nm, 255 nm, 256 nm, 257 nm, 258 nm, 259 nm, 260 nm, 262 nm, 264 nm, 266 nm, 268 nm, 270 nm, 280 nm) 3. Determination of benzene a In the colorimetric tank, "black body", "anhydrous ethanol (with anhydrous ethanol as a reference)", and "ethanol solution of benzene" are sequentially placed. b. Select a wavelength, place the “black body” on the light path, press “MODE” to “T”, press “0%” to display “000”. c. Pull “anhydrous ethanol” to the light path, press “100%”, display “100.0”, press MODE to “ABS”. d. Pull the sample to the optical path and the value displayed is the absorbance of benzene at this wavelength. e. Repeat the b-d three steps for each wavelength measurement. (Test wavelengths are: 230 nm, 240 nm, 245 nm, 250 nm, 252 nm, 253 nm, 254 nm, 255 nm, 256 nm, 257 nm, 258 nm, 259 nm, 260 nm, 262 nm, 264 nm, 266 nm, 268 nm, 270 nm, 280 nm) 5. Data processing list recording For the λ-A data, an A-λ curve is plotted on the coordinate paper to determine whether the anhydrous ethanol contains benzene. <table cellspacing="0" cellpadding="0" border="1"> <tbody> λ(nm) A </tbody></table> Six, note: 1, quartz cuvette can only pinch the scrub surface. Take it lightly on the top of the console and you can't break it. 2. The outside of the cuvette (including the bottom) must be dried with filter paper before it can be placed in the colorimetric cell. 3, a lot of negative numbers appear in the test process, contact the teacher early. 4. After the end of the experiment, do not wash the cuvette with water, let it evaporate naturally, or wash it with a small amount of absolute ethanol. Key words: ultraviolet spectrophotometry; trace benzene in ethanol; aesthetic analyzer ; UV-1100</p> </div> </div> <div class="tech-detail-share"> !-- Baidu Button BEGIN --> <div class="bdsharebuttonbox"> <a href="#" class="bds_qzone" data-cmd="qzone" title="Share to QQ Space"></a> < a href="#" class="bds_tsina" data-cmd="tsina" title="Share to Sina Weibo"></a> <a href="#" class="bds_weixin" data-cmd="weixin " title="Share to WeChat"></a> <span>Share to:</span> </div> <script>window._bd_share_config = { "common": { "bdSnsKey": {}, "bdText" : "", "bdMini": "1", "bdMiniList": false, "bdPic": "", "bdStyle": "2", "bdSize": "16" }, "share": {} }; With (document) 0[(getElementsByTagName(

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