Introduction to analytical instrumental methods

The instrumental methods are based on the measurement of some physicist-chemistry property. Its use has increased with the development of the electronics, for the facility of detecting changes in the physicist-chemistry properties and transform them to an understandable language for the humans. An analytical instrument is the support in which is developed this transformation.

This text show a small introduction for the most important instrumental methods.

• 1. Spectroscopic methods

Spectroscopy is a science that treats the interaction of the electromagnetic radiation, or other particles, with the matter.

• 1.1. Atomic Spectroscopy

In this kind of methods, the present substances in a sample, turn into atoms or elementary ions in gaseous state, for the later measurement of the analytical property.

• 1.1.1. Atomic Absorption Spectroscopy

The sample atomize by means of high temperature medium that provides a high energy. The atomizer can be a flame or a graphite furnace.
It’s radiated the atomic vapor and the atoms are able of absorbing to a characteristic length of wave. The measured absorbance will be a function of the concentration in the atomic vapor.
It’s used a hollow cathode lamp in order that the radiation that affects in the sample is typical of the element that it’s wanted to quantify.

Example of Atomic Absorption Spectrum.

• 1.1.2. Atomic Emission Spectroscopy

The most used atomizers are plasmas and the electric arch and spark. These atomizers obtain a temperature of up to 10000K.
When the sample it’s atomized with this temperature, the atoms will be in an excited state and when they return to the fundamental state they will emit a typical radiation that will be a function of the element quantity in the sample.

Example of atomic emission spectrum.

• 1.1.3. Atomic Mass Spectrometry

This method consists in atomization of the sample, conversion the atoms to ions, separation of these ions by means of the difference of the relation mass/charge (m/z) and count of the ions of every kind.
For the separation and count of ions, a mass spectrometer is used.

Example of atomic mass spectrum.

• 1.2. Molecular Spectroscopy

Are spectroscopic methods where analite that wants determinate it’s in molecular form.

• 1.2.1. Molecular Absorption Spectroscopy

The substances can absorb to a certain wavelength. If it’s radiated certain one λ, the intensity that comes to the detector will be smaller that the intensity with which we radiate the sample. This absorbance is proportional to concentration of analite, according to Beer’s Law.
Usually there is in use the region UV and Visibly of electromagnetic spectrum.

Example of Molecular Absorption Spectrum.

• 1.2.2. IR Absorption Spectroscopy

On having applied a IR radiation to a molecule, the molecule can change from some states of vibrational energy and rotational to others.
These changes are defined by a typical energy, or that is the same thing, to a certain wavelength, and it depend on the atoms that correspond to bond, to the kind of this bond and to the kind of vibration or rotation movements.

Example of IR Spectrum.

• 1.2.3. Nuclear Magnetic Resonance

It’s based on the radiation absorption on the region of the radio frequency. In this process the atomic nucleus are involved.
It’s a method for structural determination very well, since the signal of every atom, it will go out to bigger or smaller displacement, depending on the atoms that it’s around in the molecule.

Example of NMR Spectrum.

• 1.2.4. Molecular Mass Spectroscopy

It’s based on the separation of different radical or molecular ions by the difference of the relation mass/charge among them.
It’s a method of structural determination and can give information over complex mixtures, among other applications.

Example of Mass Molecular Spectrum.

• 2. Electrochemical Methods

It’s based on the electrical properties of an analite on dissolution. They possess specially low limits of detection.

• 2.1. Potentiometric Methods

It’s based on the measurement of equilibrium potential on a galvanic cell, on which we have two electrodes, indicator and reference.
We measure the potential difference between the electrodes, this potential difference between the electrodes is related to analite concentration that we want to measure.

• 2.2. Voltammetric Methods

Are methods in which the analite concentration is deduced from measurements of current intensity depending on the applied potential.
It has big advantages like that the analite doesn’t lost on having realized the experiment.

• 3. Chromatographics Methods

The chromatography is a separation method of substances in complex mixtures. It’s in use generally for separation, but some component connected to the instruments for the later determination by some analytical instrumental method.
The mixture to resolving it’s introduced in a system formed by a fluid (mobile phase), which circulates in contact with the stationary phase.
The mixture components that possess a major affinity for the stationary phase, its advance speed will become smaller and the separation will be achieved.
There are two important kinds of cromatografía:

• Gas Chromatography, where the mobile phase is an inert gas and the stationary phase can be solid or liquid.
• Liquid Chromatography, where the mobile phase is one o more liquid and the stationary phase is solid.

Example of chromatogram.

There are more instrumental methods of the described ones and these present some major complications of exposed in this text. But for a small introduction the presented here is valid.
In a future I will write an amplification of this text with more methods and a major extent in the contents.

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