Chemistry of water -Part 14-

Always in the context of water analysis, we previously discussed how to collect samples, and the conditions for keeping them pending analysis. We will continue and discuss methods of water analysis.

• Before conducting the analysis, the materials that turbid water must be disposed of, as for analysis that depend on spectral and gravimetric measurements, water turbidity can constitute a serious problem and hindrance. Another important issue is that, in the analysis of previously sterilized water (such as tap water), sodium thiosulfate is added to remove chlorine because chlorine compounds can cause disturbances in measurements based on spectrophotometric methods.

There is some necessary information that must be with the sample, as it is written down and attached to the analysis. Among this information are the following:

• The source of the water and the area from which the sample was taken.
• The type of rock through which the water to be analysed passes.
• Agricultural or industrial places close to the water source from which the sample was taken.
• The use of the water to be analysed (for drinking, washing, etc.)
• The timing of obtaining the sample and the weather.

the most common methods of water analysis for finding various pollutants:

Analytical tools like chromatographs and different spectrometers, as well as sensors, can be used to detect a chemical or biological species as well as evaluate its quantity or concentration.

Autosamplers being prepared as part of a wetland research project on water quality

1- Real-time analyses at the sampling site:

It is always better to do these assessments in the field for parameters like pH, temperature, O2, CO2, H2S, NH3, oxidation-reduction potential, and residual oxidants because they may alter during the transit of samples to the lab.

For different types of water, the measurement of dissolved oxygen is an important and essential process. Where it is preferable that the percentage of dissolved oxygen be low in the cooling water to avoid corrosion, but in drinking water, it is not acceptable that the percentage of dissolved oxygen be very low in order for the water to have a palatable taste.
The electrochemical method for measuring the percentage of dissolved oxygen is based on generating a current proportional to the partial pressure of the dissolved oxygen, using an appropriate electrode. Oxygen measuring devices give the value of the dissolved oxygen concentration in the water, and these devices contain a specific membrane that surrounds the electrode and allows the passage of oxygen.

References:

• [General and inorganic chemistry book- M. Shkhashirou- H. Birqdad- Y. Qodsi- University publications. Algeria]

• [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°]

• [GÉOCHIMIE DES EAUX CONTINENTALES- Nathalie Gassama. ISBN 9782340-047402 ©Ellipses Édition Marketing S.A., 2021. 8/10 rue la Quintinie 75015 Paris]

• [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.]

• "Chapter A2. Selection of Equipment for Water Sampling" (PDF). National Field Manual for the Collection of Water-Quality Data (Report). Techniques of Water-Resources Investigations, Book 9. Reston, VA: U.S. Geological Survey. March 2003.