Analysis of Salts

<bibimport/> Author: Hans-Jürgen Schwarz

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Abstract

In the presence of a salt load or visible salt damage, a wide variety of methods are used. The methods are presented that usually allow a quantitative determination of the salt-forming ions, or at least a qualitative determination of individual ions or salt phases. The measuring principle, the application and the advantages of each method are briefly outlined.

Mikroscopy

With the help of the polarizing microscope, the various salts are determined based on their optical properties. This includes in particular the study of the birefringence and light refraction of the salts. Compared to normal by light microscopy the polarizing microscope has two polarizers - the polarizer and the analyzer. The analyzer is used to recognize the optical properties of a salt by the change of the linearly polarized light due to the salt.

Microchemistry

With micro-chemical reactions, a salt analysis can be performed on very small samples. Usually this is done using a microscope (polarizing microscope). This method can also be quite convenient locally at the object. The micro-chemical analysis of salt consists in the qualitative detection of individual salt ions in more or less concentrated aqueous solution.

X-Ray Diffraction Analysis (XRD)

With the XRD analysis, qualitative and quantitative salt analyses are carried out. When X-rays hit a crystalline material a series of "reflections" are produces which are characteristic for each phase like a "fingerprint". It is a laboratory method and the amount of the sample can be quite small with special sample holders.

Atomic Absorption Spectroscopy(AAS)

The atomic absorption spectroscopy is a method that allows rapid and accurate quantitative determinations of many elements. Since the method relies on the energy absorption by free atoms, it can usually be used without prior separation or isolation steps of other elements present in the sample. The quantity of sample needed for analysis is low. Element concentrations of a millionth (ppm) or one billionth part (ppb) of the sample can be detected.

Inductively coupled plasma (ICP)

An inductively coupled plasma (ICP) is a type of plasma source in which the energy is supplied by electric currents which are produced by electromagnetic induction, that is, by time-varying magnetic fields. It is used e.g. in atomic emission spectroscopy (ICP-AES) or in mass spectrometry (ICP-MS). The inductively coupled plasma uses in a the high-frequency field (27 MHz) ionized gas (argon), which serves as an atomization and excitation medium for the sample. It can be used to detect very low concentrations of the analysed elements in the order of one millionth (ppm) or one billionth part (ppb) in the sample.

Ion chromatography (IC)

Ion chromatography (or ion-exchange chromatography) is a process that allows the separation of ions and polar molecules based on their charge. It is a process for the separation of substances, and these are differently distributed between a stationary and a mobile phase. In ion chromatography, the ions bound to the stationary phase are later released by an eluent in the mobile phase. Quantification is achieved using a suitable detector. Using specific columns, both anions and cations are determined quatitativly in low concentrations.

Photometry

The basic principle of photometry is to produce a colored or light-absorbing solution. The ion to be determined or element is incorporated into a stable, colored and soluble compound or transferred, or it triggers a reaction and color controls. With a photometer the absorption of monochromatic radiation through the solution is measured. Quantitative analysis of anions and cations in a sufficient accuracy is possible.

the mathematical difference between the largest and smallest refractive index for an anisotropic mineral

X-ray diffraction

a method to determine chemical elements employing the absorption of optical radiation (light) by free atoms in the gaseous state.

In physics and chemistry, plasma is a state of matter similar to gas in which a certain portion of the particles are ionized. A very high heating over a few thousand K leads to ionization, thus turning it into a plasma, containing charged particles.

Inductive Coupled Plasma, method for analysing chemical elements.

carrier liquid or mobile phase of a gas

In physics, monochromatic refers to electromagnetic radiation of a single frequency.