New total hardness (Calcium and Magnesium) automated titration method case study


Courtesy of Courtesy of MANTECH INC.

MANTECH INC. is a leading manufacturer of automated multi-parameter, titration, Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) laboratory and process instruments. MANTECH developed the first automated software based titration system in the world. By listening to our environmental customers, MANTECH understood the need to develop a new total hardness (calcium and magnesium) titration method for water analysis.

The current total hardness method uses an ammonium hydroxide (NH4OH) based buffer. The disadvantages of this buffer are:

  1. An unpleasant strong odor that can also have a negative effect upon personnel with breathing conditions such as asthma. As a result of this, the total hardness titration station is often placed in a fume hood which is expensive.
  2. With a multi-parameter analysis system that also analyses pH and alkalinity, the NH4OH buffer will often shock the pH electrode causing a memory of the NH4OH pH value. This then takes significant conditioning and time before the pH electrode can be used for pH and alkalinity analysis of the next sample. As a result of this, analysis of total hardness is normally completed in a separate batch run (not true multi-parameter from a single sample) or the environmental laboratory invests in two (2) autosamplers to separate the analysis stations and electrodes. Both increase the operating costs of the automated system leading to a poor return on the investment.

MANTECH introduced the RapidDuo which effectively solved number 2 above, using one AutoMax sampler and offering true multi-parameter analysis from a single sample cup. However, number 1 was not solved.

MANTECH has developed a new buffer formulation and validated the hardness titration method using this. The reagent isTRIS (tris(hydroxymethyl)aminomethane)/Acetylacetone Buffer.The Application Note #126 may be downloaded here.

It has resulted in the following advantages.

  1. The pH of the sample is still increased to above 10 without shocking the pH electrode.
  2. This potentiometric titration method with TRIS buffer resulted in improved endpoint detection for both the Calcium and Magnesium endpoints. Accuracy and precision are improved.
  3. This potentiometric titration method utilizes the Calcium ion selective electrode. Color indicators are not required and total, calcium and magnesium hardness are determined form a single titration method. This saves considerable time and money for the laboratory.
  4. It offers multi-parameter analysis from a single cup, in a single analysis vessel, including pH, alkalinity and total hardness. This results in operational savings for environmental laboratories thereby optimizing the return on investment with MANTECH systems.
  5. Additional parameters such as conductivity, turbidity, fluoride, chloride, color and dissolved oxygen are easily added.

The MANTECH Total Hardness Titration method with TRIS buffer is a robust water analysis method generating accurate and precise results that stand the test of time.

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