Which of the following statements regarding electron-impact mass spectrometry is true?a)Samples need isotopic labels.b)The base peak is formed by loss of one electron from each vaporised molecule by an electron beam.c)Compounds must have a functional group to show a mass spectrum.d)A meaningful mass spectrum can sometimes be obtained on a very small sample of an impure compound.Correct answer is option 'D'. Can you explain this answer?

Question

Answer

For the electron-impact mass spectrometric method. A mass spectrum records relative abundances of the molecular cation and its fragment cations by their mass-to-charge ratios, m/z. The base peak corresponds to the most abundant cation which is not usually the molecular cation. Mass spectrometric signals of impurities do not normally obscure the significant peaks of the main compound; in fact, mass spectrometry is a useful technique for identifying impurities.

Answer

Importance of Electron-Impact Mass Spectrometry
Electron-impact mass spectrometry is a valuable technique used to determine the molecular weight and structural information of compounds. Here's why a meaningful mass spectrum can sometimes be obtained on a very small sample of an impure compound:

Minimal Sample Requirement
- Electron-impact mass spectrometry can provide useful data even with small sample sizes, making it a versatile tool for analyzing limited or impure samples.
- The technique involves bombarding the sample with high-energy electrons, leading to the formation of charged fragments that are separated based on their mass-to-charge ratios.

Information Obtained
- The base peak, which is the most intense peak in the mass spectrum, is typically formed by the loss of one electron from each vaporized molecule by the electron beam.
- By analyzing the fragmentation pattern of the ions produced, valuable information about the compound's structure, functional groups, and isotopic composition can be obtained.

Functional Groups Not Required
- Unlike some other analytical techniques, electron-impact mass spectrometry does not require compounds to have specific functional groups to produce a mass spectrum.
- This versatility allows for the analysis of a wide range of compounds, including those with complex structures or impurities.
In conclusion, electron-impact mass spectrometry is a powerful tool for analyzing compounds, even in small or impure samples, due to its ability to provide meaningful mass spectra without the need for isotopic labels or specific functional groups.

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