Chapter 22, Problem 22.8P

(a)

Interpretation Introduction

Interpretation:

Nominal mass of the molecular ion of caffeine has to be determined. Reason behind the use of $\frac{\text{m}}{\text{z}}197\to 111$ for the internal standard ${\left(\text{C}{\text{H}}_{\text{3}}\right)}_{\text{3}}-\text{caffeine}$ has to be explained.

Concept Introduction:

An internal standard in mass spectrometry is a compound that is chemically similar to the analyte but naturally not present in the sample. It displays characteristic signals in the mass spectrum.

(b)

Interpretation Introduction

Interpretation:

Reason for isotopic variant of the analyte to be excellent internal standard has to be explained.

Concept Introduction:

Refer to part (a).

(c)

Interpretation Introduction

Interpretation:

Isotopic composition of composition of $\frac{\text{m}}{\text{z}}$ 195 has to be written. Intensity ratio $\frac{\text{m}}{\text{z}}\frac{195}{194}$. $195/194$ has to be calculated.

Concept Introduction:

An internal standard in mass spectrometry is a compound that is chemically similar to the analyte but naturally not present in the sample. It displays characteristic signals in the mass spectrum.

Intensity ratio of $\frac{\text{M}+\text{1}}{\text{M}}$ for the molecular formula ${\text{C}}_{\text{n}}{\text{H}}_{\text{x}}{\text{N}}_{\text{y}}{\text{O}}_{\text{z}}$ is calculated by formula as follows:

    $\text{Intensity ratio}=\text{n}\times 1.1\%$