Calculate the Kovats retention index for an unknown using the following retentio

Question

Calculate the Kovats retention index for an unknown using the following retention times: 2.0 min for CH4, 12.4 min for octane, 14.1 min for the unknown, and 17.5 min for nonane.

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Calculate the Kovats retention index for an unknown using the following retention times: 2.0 min for CH4, 12.4 min for octane, 14.1 min for the unknown, and 17.5 min for nonane. Number Previous Give Up & View Solution O Check Answer Next Exit The Kovats retention index of an unknown compound is calculated using the formula log t unknown))- log t. (n = 100|" + (N-")-log(, (N))-loge (")

Explanation / Answer

I= 100 [ n + (N-n) [ log tr(unknown) - log tr(n)] / [ log tr(N) - log tr(n)]

where n is the number of carbon atoms in the smaller of the two known linear alkanes,N is the number of carbon atoms in the larger of the two known linear alkanes, tr'(n) is the adjusted retention time of the smaller of the two known linear alkanes, tr' (N) is the adjusted retention time of the larger of the two known linear alkanes, tr'(unknown) is the adjusted retention time of the unknown. The adjusted retention time is given by the equation,

tr'= tr - tm, where tr is the retention time of the solute and tm is the time required for unretained solute (CH4) to be eluted from the column. In this case, the adjusted retention time values are:

tr'( C8H18)= 12.4-2.0 = 10.4 min

tr'(C9H20)= 17.5 - 2.0= 15.5 min

tr'(unknown)= 14.1 - 2.0 =12.1 min

So, the reaction index is,

I = 100[8 +(9-8)[ log tr (12.1)- log tr(10.4)]/ [ log tr(15.5) - log tr (10.4)]] = 837.941

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