An isotopic variant of toluene (toluene-d_8, C_7 D_8, all hydrogen atoms replace

Question

An isotopic variant of toluene (toluene-d_8, C_7 D_8, all hydrogen atoms replaced by deuterium) was used as an internal standard in GC/MS analysis of toluene in gasoline. At the maximum of the chromatographic peak for the two co-eluting toluene isotopes, the m/z 91 (the base peak in a toluene mass spectrum) ion signal was found to be 1.43 times the corresponding peak from the isotopic variant. a.) At what nominal mass (m/z) do you expect to find the biggest peak for the isotopic variant? b.) Given that the only other significant peak in the mass spectrum of toluene is the molecular ion peak at about 60% relative abundance (vs. the m/z =91 base peak at 100%) sketch the mass spectrum (from m/z 91 up) that you would expect to observe in this experiment. c.) Given that the concentration of the internal standard added to the sample was 10.0 mu M, what is the concentration of the toluene? d.) Give two advantages that this internal standard method might have over other methods that could be used for measuring toluene in this sample. Also give one significant disadvantage of this method of.

Explanation / Answer

Internal standard method can be used in liquid chromatography (LC) and has the following advantages.

1. It increases the precision and accuracy of come LC methods.

2. Corrects uncontrolled sample losses during sample preparation

THe diadvantages are as follows.

1 Not convenient and may be expensive

2. May lead to the chromatogram to be complex with interfering peaks

3. The uncertainty of the results may be higher because the variability in IS addition and IS peak measurement

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