英语翻译As mentioned above,the retention time of a compound unde

英语翻译
As mentioned above,the retention time of a compound under a specified set of conditions is a physical constant that can be used in qualitative analysis.For example,you might wish to use p-xylene as a reagent,but might suspect that a commercial sample of the compound is contaminated with small amounts of o-xylene and m-xylene.If your suspicion is correct.you will find that a vapor-phase chromatogram of the reagent shows one major peak and two minor peaks.You can then confirm your suspicion as to the nature of one of the contaminants by deliberately adding some o-xylene to the reagent and obtaining a new vapor-phase chromatogram1.If the contaminant in the reagent is indeed o-xylene,one of the minor peaks will be larger in the second chromatogram than in the first.The same type of control experiment can then be carried out with addition of w-xylene to the reagent.Alternatively,the retention times of pure o-xylene and m-xylene can be obtained under the same conditions as used for the reagent,p-xylene.The retention times of the two impurities present in the p-xylene should correspond to those of pure o-xylene and m-xylene,respectively,if these are the impurities.Reasonable care must be exercised in the interpretation of vapor-phase chromatograms for purposes of qualitative analysis.Just as two different solid compounds may possess the same or very nearly the same melting point,two different volatile compounds may exhibit identical retention times under a given set of conditions.Thus,it is usually wise to confirm a tentative identification of a compound through its retention time by some other means2.One of the best ways to do this is to condense the compound as it leaves the detector unit of the gas chromatograph,take the infrared spectrum of the condensate and then compare it with the.spectrum of the compound whose presence is suspected.
\x05Molarity is the number of moles (gram-molecular weights)of substance per liter of solution.The mole weight of sulfuric acid is 98.08 g,and therefore,1 mole of H2SO4 contains 98.08 g.If 49.04 g are diluted to 1 liter then the concentration is 0.49 or 0.5M.In the case of hydrochloric acid,HCl,a 1 M solution is prepared by taking 36.465 g of HC1 and diluting to 1 liter.The procedure is the same for bases.
\x05Normality is the number of equivalent weights of substance per liter of solution.The equivalent weight of an acid is the weight of that acid capable of furnishing 1 mole of protons (H+),and the equivalent weight of a base is the weight of base capable of receiving 1 mole of protons.The equivalent weight of H2SO4 is 98.08g/2 or 49.04 g.Therefore,a normal solution (N)of H2SO4 contains 49.04g per liter.

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