Chemistry of water -Part 25-
Chromatography is a physico-chemical method that allows the separation of the components of a mixture based on the distribution of those components between two immiscible phases. The first phase consists of a solid and settles within the separation column, and the phase of the sample carrier liquid passing through the separation column where it comes in contact with the stationary phase, and within the column the compounds or ions are separated from each other before passing through the detection device.
The stationary phase works to capture the ions and fix them on its surface, while the mobile phase works to remove them and carry them with it, and the balance between these two actions leads to the separation of those ions that make up the sample to be analysed, and thus it crosses the detection system in succession, and the analysis technique becomes possible When the distribution coefficient of the compounds or electrolytes making up the mixture is different in its value.
Calibration of ions dissolved in water using chromatography:
The term ion chromatography was introduced into analytical chemistry in 1975 with the advent of the conductivity-dependent detection system, and this technique is considered good compared to other techniques used in water analysis at the present time.
Ion chromatography method, which belongs to the high-performance liquid chromatography system, is employed in a very broad variety of applications for the measurement of electrolytes in aqueous medium. Modern equipment provide outstanding accuracy in analysis and ease of use.
The process of analysis by ion chromatography includes a number of stages, and the equipment used has basic specifications, including that the materials in contact with the liquid phase are inert, non-oxidizable, and bear high pressure, and are connected by small diameter tubes (0.1 mm). The equipment also includes a pump that ensures that the mobile phase passes through the separation column at high pressure that reaches tens of bars. It is necessary to remove gases from the mobile phase solution using inert gases.
The ion chromatography technique allows calibration of a mixture of ions in the water sample at the same time, and therefore we do not need to analyse each ion separately as is the case in other methods of analysis.
References:
[AQUAPROX- Livre: Traitement des eaux de refroidissement. Imprimé en France par EMD S.A.S- 53110 Lassay-les-Chateaux. N° d'imprimeur: 15566- Dépot légal: juin 2006. N° 842- Cyclus print 90°]
[Introduction to Water Chemistry (Pollution- Treatment- Analysis). Dr. Nasser Al-Hayek. Publication of the Higher Institute for Applied Sciences and Technology (HIAST). Syrian Arab Republic, 2017.]
Folco Laverdière, Anja Holstein, Laurent Thiebaut, Robert Mallee, Guillaume Gravejat, Benjamin Des clozeaux: Les principales methodes d’analyse,1999, p5.