Mass Spectrometry MCQ Quiz in मराठी - Objective Question with Answer for Mass Spectrometry - मोफत PDF डाउनलोड करा

Explanation:

• The metastable ion appears at an M/Z ratio that depends on its mass as well as the mass of the original ion from which it formed in the mass spectrum.
• The metastable ion peaks are usually broad peaks.
• The apparent mass of the metastable ion (m*) is given by-

m₁* → m₂* + fragment

\(m^{*}=\frac{\left ( m_{2} \right )^{2}}{m_{1}}\)

where m₁ is the mass of the original ion from which the fragment formed and m₂ is the mass of the new fragment ion.

• Thus, the mass of the metastable ion is produced due to the decomposition of F₁⁺ in the following mass fragmentation sequence is calculated as-

Diethyl phthalate → F1+ → F2+ + CO

( M+, 222)               (177)   (149)   (28)

\(m^{*}=\frac{\left ( m_{2} \right )^{2}}{m_{1}}\)

\(m^{*}=\frac{\left ( 149 \right )^{2}}{177}\)

= 125.4

Conclusion:-

• Hence, the mass of a metastable ion is 125.4

Concept:-

• Mass spectrometry is an analytical tool useful for measuring the mass-to-charge ratio (m/z) of one or more molecules present in a sample.   
• A mass spectrum is a histogram plot of intensity vs. mass-to-charge ratio (m/z) in a chemical sample, usually acquired using an instrument called a mass spectrometer.
• In a typical MS procedure, a sample, which may be solid, liquid, or gaseous, is ionized, for example by bombarding it with a beam of electrons. This may cause some of the sample's molecules to break up into positively charged fragments or simply become positively charged without fragmenting.

• These ions (fragments) are then separated according to their mass-to-charge ratio, for example by accelerating them and subjecting them to an electric or magnetic field: ions of the same mass-to-charge ratio will undergo the same amount of deflection.

Explanation:

Mass spectrum of Alcohols:

• An alcohol's molecular ion is small or non-existent.
• Cleavage of the C-C bond next to the oxygen usually occurs and the largest alkyl group is most readily lost.
• A loss of H₂O may occur as in the spectra below.

Example: 3-Pentanol (C5H12O) with MW = 88.15

In the case of 3-Pentanol (C5H12O), two -CH₂CH₃ group is present next to the oxygen atom, and thus dissociation of one of the -CH2CH3 group results in a peak at 59 (m/z).

• In the mass spectrum of the tertiary alcohol below the order of size of the different alkyl groups are as follows:

C3H7>Et>Me

• As, the largest alkyl group is most readily lost in tertiary alcohol, thus the order of a preferential loss of groups is

 C3H7>Et>Me

Conclusion:-

• Hence, the order of a preferential loss of groups is

C3H7>Et>Me