Supelco MQuant Carbonate Hardness Test Instructions

Supelco MQuant Carbonate Hardness Test

INSTRUCTION MANUAL

1. Definitions

The hardness is defined as the content of calci-um ions, Ca2+, and magnesium ions, Mg2+, (“hardness ions”) in a water.
The units for the water hardness relate to calci-um or its compounds CaO (1 °d ^= 10 mg/l CaO) or CaCO3 (1 °e ^= 14.25 mg/l CaCO3; 1 °f ^= 10 mg/l CaCO3), with the magnesium content being expressed as calcium content and includ-ed in the calculation accordingly.

Carbonate hardness (“temporary hardness”) is that proportion of hardness ions for which there is an equivalent amount of anions of car-bonic acid (hydrogen carbonate, HCO3-, and car-bonate, CO32-).
The concentration ratio between HCO3- and CO32- is dependent on the pH value. Therefore, in nat-ural waters (pH < 8) the carbonate hardness in mmol/l Ca approximately corresponds to the equivalent concentration of the hydrogen car- bonate ions (1 mmol/l Ca ^= 2 mmol/l HCO3-).

2. Method

Hydrogen carbonate and carbonate ions react with acid. The resultant change in the pH influ-ences the color of a mixed indicator. The carbon-ate hardness is measured semiquantitatively by visual comparison of the reaction zone of the test strip with the fields of a color scale.

3. Measuring range and number of determinations

4. Applications

Sample material:

Drinking water
Mineral water (after degassing)
Groundwater and surface water
Industrial water
Aquarium water
This test is not suited for seawater.

5. Influence of foreign substances

The determination is interfered with when the water sample contains – in addition to the salts of carbonic acid – strong bases or buffering sub-stances such as phosphates and polyphos-phates. Flocculating and precipitating agents that bind hydrogen carbonate and carbonate ions produce a false-low carbonate- hardness result.

6. Reagents and auxiliaries

The test strips are stable up to the date stated on the pack when stored closed at +15 to +25 °C.

Package contents:
Tube containing 100 test strips

Other reagents:
MQuant® Total Hardness Test, Cat. No. 1.10046, measuring range >6 – >31 °e

7. Preparation

Degas strongly carbonic acid-containing waters (e. g. carbonated mineral water) at room tem-perature by stirring or ultrasound.

8. Procedure

Immerse the reaction zone of the test strip in the pretreated sample (15 – 30 °C) for 1 sec.
Shake off excess liquid from the strip and after 1 min determine with which color field on the label the color of the reaction zone coincides most exactly.

Read off the corresponding result.

Notes on the measurement:

• The color of the reaction zone may continue to change after the specified reaction time has elapsed. This must not be considered in the measurement.
• The total hardness should also always be determined in addition to the carbonate hardness.

This is because in some cases the value found for the carbonate hardness is apparent-ly higher than that for the total hardness
(“hardness inversion”). In this case the value measured for the total hardness must be taken as that for the carbonate hardness actually present.

The “hardness inversion” can be explained by the fact that as a rule – in addition to the hardness ions Ca2+ and Mg2+ – other cations are also dissolved in the water and hence under certain circumstances more equivalents of carbonic acid anions than of hardness ions are present.

9. Conversions

10. Note

Reclose the tube containing the test strips immediately after use.

MilliporeSigma is the U.S. and Canada Life Science business of Merck
KGaA, Darmstadt, Germany.

© 2023 Merck KGaA, Darmstadt, Germany and/or its affiliates. All Rights Reserved.

MilliporeSigma, Supelco, Sigma-Aldrich, and MQuant are trademarks of Merck KGaA, Darmstadt, Germany or its affiliates. All other trademarks are the property of their respective owners. Detailed information on trademarks is available via publicly accessible resources.

EMD Millipore Corporation, 400 Summit Drive Burlington MA 01803, USA, Tel. +1-978-715-4321
www.sigmaaldrich.com/mquant

MilliporeSigma Canada Ltd., 2149 Winston Park Dr, Oakville, Ontario, L6H 6J8, Canada
Phone: +1 800-565-1400

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