30 Jul

Detectando iones

Figure 1. Ionization by ESI

Atoms, in order to be deflected by magnetic or electric fields, must first be ionized by bombardment of a beam of electrons, giving rise to positively charged particles. Those electrons act like billiard balls, removing electrons from the sample. This is achieved by passing the sample in solution through a capillary to which an electrical potential is applied. At the outlet of the capillary, the solution disperses in the form of a spray, forming small charged droplets, which evaporate rapidly. This is known as electrospray ionization (ESI).

Next, the positive ions leave the ionization chamber by the force of an electric field provided with a positively charged network (repels) and a negatively charged network (attracts). Because the attractive and repulsive forces act in the same direction, the ions will move rapidly toward the negatively charged lattice. The lighter ions will “travel” faster than the heavier ions.

The main job of the mass analyzer is to apply an external magnetic field to the ions leaving the ionization chamber. This external field interacts with the magnetic field generated by the moving particles, causing the trajectory of each particle to bend slightly. The number of curves in an ion’s path depends on two factors: its mass and its charge. This is known as the (m / z) ratio, where lighter, higher-charged ions deflect more than heavy ions with a smaller charge. Therefore, each ion follows a path that depends on its mass.

Detecting ions

Atoms, in order to be deflected by magnetic or electric fields, must first be ionized by bombardment of a beam of electrons, giving rise to positively charged particles. Those electrons act like billiard balls, removing electrons from the sample. This is achieved by passing the sample in solution through a capillary to which an electrical potential is applied. At the outlet of the capillary, the solution disperses in the form of a spray, forming small charged droplets, which evaporate rapidly. This is known as electrospray ionization (ESI).

Next, the positive ions leave the ionization chamber by the force of an electric field provided with a positively charged network (repels) and a negatively charged network (attracts). Because the attractive and repulsive forces act in the same direction, the ions will move rapidly toward the negatively charged lattice. The lighter ions will “travel” faster than the heavier ions.

The main job of the mass analyzer is to apply an external magnetic field to the ions leaving the ionization chamber. This external field interacts with the magnetic field generated by the moving particles, causing the trajectory of each particle to bend slightly. The number of curves in an ion’s path depends on two factors: its mass and its charge. This is known as the (m / z) ratio, where lighter, higher-charged ions deflect more than heavy ions with a smaller charge. Therefore, each ion follows a path that depends on its mass.

Of all the ions that pass through the mass analyzer there will be many that we are not interested in. For which we filter the ion stream that interests us, making them reach the detector, which will give us the mass spectrum. This mass spectrum is represented by an X axis with the mass of the different ions and a Y axis that gives us the relative intensity. Below is an example of a mass spectrum of capsaicin in which we can see its molecular ion of 305 (Figure 2). A compound not so unknown to people who enjoy spicy foods. On another occasion we will talk about this interesting molecule.

Figure 2. Mass spectrum of capsaicin.

Of all the ions that pass through the mass analyzer there will be many that we are not interested in. For which we filter the stream of ions that interest us, making them reach the detector, which will give us the mass spectrum. This mass spectrum is represented by an X axis with the mass of the different ions and a Y axis that gives us the relative intensity. Below is an example of a mass spectrum of capsaicin in which we can see its molecular ion of 305 (Figure 2). A compound not so unknown to people who enjoy spicy foods. On another occasion we will talk about this interesting molecule.