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[求助]
GC-MS求助
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小弟初涉GC，分析是遇到几个问题： 1、 分析的化合物组分在相同的条件下，在图谱中同种的化合物应该有相同的relative retention time。即同种化合物的峰在重复的分析中应该是完全重叠，但是有没有可能虽然是同一种物质，retention time 有微小的差别，在图上看，峰是部分或者不重叠？ 2、在利用Mass Spectrometer检测化合物时，同种的化合物使用同一台检测器，是不是会出现质谱图的一些小偏差，不完全一样？ 3、在使用GC-MS确定化合物时，我看到的文献是将自己的retention time划算成Kovats retention index，再结合自己的质谱图和化合物的衍生（derivation）对照Library和前人的工作来判断自己的物质成分，这个Kovats retention index换算具体怎么操作？这样判断是否准确？大家是怎么样确定自己的未知化合物的？ 虽然在Library里有可能找到相似度较高的物质，但是又怎样确定呢？ 希望各位大虾知道几个说几个，不吝赐教！谢谢 |
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Kovats retention index (shorter Kovats index, retention index; plural retention indices) is a concept used in gas chromatography to convert retention times into system-independent constants. The index is named after the Hungarian-born Swiss chemist Ervin Kováts, who outlined this concept during the 1950s while performing research into the composition of the essential oils.[1][broken_link] The retention index of a certain chemical compound is its retention time normalised to the retention times of adjacently eluting n-alkanes. While retention times vary with the individual chromatographic system (e.g. with regards to column length, film thickness, diameter, carrier gas velocity and pressure, and void time), the derived retention indices are quite independent of these parameters and allow comparing values measured by different analytical laboratories under varying conditions. Tables of retention indices can help identify components by comparing experimentally found retention indices with known values.[2] [3] [4] [edit]Expression The method takes advantage of the linear relationship between the values of and the number of carbon atoms in a molecule. The value of Kovats index is usually represented by I in mathematical expressions. Its applicability is restricted to organic compounds. For isothermal chromatography, the Kovats index is given by the equation Where: Kovats retention index, the number of carbon atoms in the smaller n-alkane, the number of carbon atoms in the larger n-alkane, the adjusted retention time. For temperature programmed chromatography, the Kovats index is given by the equation Where: Kovats retention index, the number of carbon atoms in the smaller n-alkane, the number of carbon atoms in the larger n-alkane, the retention time. 这是维基的解释，不是可以换算的吗？ |
3楼2013-02-25 06:31:36