Quantitative Analysis of Compounds and Mixtures

Quantitative analysis of compounds can be performed by measuring the relative intensities of a spectral peak or peaks unique to the compound and comparing the intensity of the sample to a series of known standards of the compound. The use of isotope dilution for quantitative measurements 

Quantitative analysis can also be performed by external calibration or by the use of an internal standard that is not a labeled analyte molecule but a compouud that is uot preseut in the sample. 

In some cases, components in a mixture can be determined quantitatively without prior separation if the mass spectrum of each component is sufficiently different from the others. Suppose that a sample is known to contain only the butanol isomers listed in Table 10.17. It can be seen from Table 10.17 that the peak at miz = 33 is derived from butanol, but not from the other two isomers. A measurement of the miz = 33 peak intensity compared to butanol standards of known concentration would therefore provide a basis for measuring the butanol content of the mixture. Also, we can see that the abundances of the peaks at m z = 45, 56, and 59 vary greatly among the isomers. Three simultaneous equations with three unknowns can be obtained by measuring the actual abundances of these three peaks in the sample and applying the ratio of the abundances from pure compounds. The three unknown values are the percentages of butanol, 2-butanol, and 2-methyl-2-propanol in the mixture. The three equations can be solved and the composition of the sample determined. Computer programs can be written to process the data from multicomponent systems, make all necessary corrections, and calculate the results. 

Hexanoic acid, ethyl ester 88.05026 C4H302 Fragment 88.05243 -2.2 

Hexanoic acid, ethyl ester 99.07999 QHuO Fragment 99.081 -1 

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