Briefly describe how to determine the molecular ion peaks in mass spectrometry analytical method

Mass Spectrometry

I. Basic Requirements for Teaching

Master the basic principles of mass spectrometry,

general rules of compound cleavage,

characteristics of molecular ion peaks and methods of determination,

mass spectrometry

methods for resolving. Be able to recognize molecular ion peaks, radical peaks, and fragment ion peaks in a mass spectrogram. Understand the main components of a mass spectrometer

parts and functions.

II. Basic Concepts and Key Points

1

.

Principle, characteristics and role of mass spectrometry

2.

Working process and principle of mass spectrometry

3.

Types of ion peaks in the mass spectrometry

There are molecular ion peaks, isotope ion peaks, fragmentation ion peaks, rearranging ion peaks, stabilizing ion peaks, and radical peaks.

4

. The molecular ion peak

is generally the peak with the largest mass-to-charge ratio (

m/z

) in the mass spectrum. From the

m/z

of the molecular ion peak, the relative molecular weight

of the compound can be obtained,

and its relative intensity can be a rough indication of the type of compound being tested.

But it is important to note that not all compounds

have molecular ion peaks.

5

. Isotope ion peaks

6

. Fragmentation ion peak

7

. Stable ion peak

8

. Base peak

The fragment ion peak with the greatest relative intensity in the mass spectrogram.

9

. Method of determining molecular ion peaks

10

. Order of stability of molecular ion peaks of organic compounds

Aromatic compounds > *** conjugated alkenes > olefins > alicyclic compounds > straight-chained alkanes > ketones > amines > esters > ethers > acids > branched-chained alkanes

> > alcohols.

11

.

N

Law

(

1

) An organic compound consisting of C, H, and O,

M

must be even.

(

2

) An organic compound consisting of C, H, O, N,

N

Odd and

M

Odd.

(

3

) Organic compounds consisting of C, H, O, and N,

N

even,

M

even.

The mass difference between the molecular ion peak and the neighboring peaks must be reasonable.

12

. General Methods of Mass Spectrogram Resolution

1) The molecular ion peaks are identified from the high mass end of the mass spectrogram to derive the molecular weight of the compound.

②Look at the isotopic peak sets of the molecular ion peaks and determine the compositional formula of the compound from the isotopic abundance ratios of the elements.

(iii) Calculate the degree of unsaturation of the compound from the constitutive formula,

Determine the compound species,

number of rings and unsaturated bonds,

and further speculate on the structure of the

compound.

④Study the fragmentation ion peaks at the high and low mass ends separately, analyze the possible pathways of molecular fragmentation, the characteristic ions generated,

determine the substituents that may be contained in the compounds, and speculate on the type to which the compounds belong.

⑤ Studying the stabilizing ion peaks to find out the interrelationships between certain ions and to further propose the structure of the compound.

⑥Combine the above analytical studies,

from the several possible structures postulated,

confirm the structure that best matches the mass spectrometry data,

and at the same time combine

the physicochemical properties of the samples, infrared, NMR, and other information, to determine the structure of the compounds.