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Water analysis is typically characterized by a combination of high sample numbers, determining multiple parameters and, rapid, straightforward testing processes. This combination of factors is key to the comprehensive analysis of sample types such as tap and wastewater.

Potentiometric techniques are employed in the determination of the majority of analytical parameters, for example, titration, pH measurements, conductivity or direct measurements via ion-selective electrodes (ISE).

A potentiometric titrator is, therefore, one of the most popular instruments for water analysis.

The whole workflow can be automated to achieve high sample throughput. This is made possible through the use of an InMotion Max 100 mL Autosampler that is connected to a Titrator Excellence T9 or T7, facilitating the unattended sample preparation and analysis of up to 55 samples.

This article explores the use of automatic sample volume adjustment to effectively measure temperature, conductivity, pH value, alkalinity by p- and m-values titration and Ca-/Mg-hardness in tap water.

Image Credit: Mettler-Toledo - Titration

Sample size should be initially adjusted to the correct value by pumping out any excess tap water.

The InMotion Max’s titration head should be initially moved to the position labeled “Conductivity measurement” in order to enable both conductivity and temperature measurements.

The titration head should be fully lowered to the position labeled “Sample” in order to facilitate pH determination.

After the pH value has been measured, the alkalinity (p- and m-values) can be ascertained by titration with 0.1 M HCl. The p- (phenolphthalein value) and m- (methyl orange, m-value) values are then calculated at potentials pH=8.2 and pH=4.3.

A 10 mL pH 8.5 0.2 M TRIS/acetylacetone buffer will be automatically added using a burette to facilitate the selective determination of calcium and magnesium.

Next, the sample is titrated with 0.1 M EDTA to determine Ca- and Mg-content. This also enables a calculation of total water hardness. The titration can be monitored through the use of a combined perfectION Ca-ISE.

Alkalinity: expressed as mmol/L M=1 g/mol, z=1 or as mg CaCO3/L M=100.09 g/mol, z=1

Ca2+ + H2EDTA2- → Ca-EDTA2- + 2 H+

Mg(acac)2 + H2EDTA2- → Mg-EDTA2- + 2 H+ + 2 acac-

pH 8.5 buffer THAM/Acetylacetone, 0.2 mol/L:

A total of 24.228 g of THAM (0.20 mol/L) should be added into a 1000 mL volumetric flask along with 10.01 g of acetylacetone (0.1 mol/L). This should be dissolved, and the flask filled up to the mark with deionized water.

* No results for p-value since initial pH value lower than pH 8.2 for this water sample.

Results consistently demonstrated very good reproducibility, as highlighted by the relative standard deviation (srel).

It should be noted, however, that the p-value could not be evaluated because the initial pH is below 8.2. No result was therefore acquired when titrating with 0.1 M HCl.

This information has been sourced, reviewed and adapted from materials provided by Mettler-Toledo - Titration.

For more information on this source, please visit Mettler-Toledo - Titration.

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