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Alkalinity

Alkalinity is the ability of a substance to resist a change in pH and defined as the buffering capacity of a solution. This resistance affects how much acid is needed to adjust the pH of a solution. Alkalinity is typically measured as mg/L of Calcium Carbonate (CaCO3). The higher the alkalinity of the water, the more resistant it will be to a change in pH. The lower the alkalinity, the easier that the pH can change. This concept is reflected in the differences with groundwater versus surface water. In certain areas the alkalinity is very high because rainwater dissolves calcium carbonate as it percolates through the soil. Because alkalinity is a general parameter that influences a wide variety of processes it is an important parameter to measure for growers (including hydroponics and aquaponics), saltwater aquarists, food and beverage industries, and pools and spas to name a few.

Alkalinity can be measured as Phenolphthalein Alkalinity or Total Alkalinity. The Phenolphthalein Alkalinity is determined by neutralizing the sample to a pH of 8.3 using a dilute hydrochloric acid solution and a phenolphthalein indicator. This process converts hydroxide ions to water, and carbonate ions to bicarbonate ions:

OH- + HCl → H2O + Cl-→ CO3-2 + HCl → HCO3- + Cl-

Since bicarbonate ions can be converted to carbonic acid with the addition of hydrochloric acid, the Phenolphthalein Alkalinity measures total hydroxide ions, but only half of the bicarbonate contribution. To completely convert the carbonate ions, hydrochloric acid is added until the sample pH is 4.5, which is known as Total Alkalinity: 

HCO3 - + HCl → H2CO3 + Cl-

 

Titration

Hanna Instruments offers a variety of titration systems.

Potentiometric titration systems include single and dual channel options along with version with a single or dual dosing pump. These systems are the most accurate in dosing with a 40,000 step dosing pump that can deliver microliters of titrant.

The mini-titrator is a Hanna Instruments innovation to bring the accuracy and precision of our potentiometric titration systems to the users that are performing manual titration with a pH meter. The mini-titrators use a syringe pump to accurately dose the titrant. The titrant is pre-standardized so no specialized glassware or analytical balances are need to make the titrant.

 

 

 

Portable pH Meters

We offer a variety of portable pH meters that can be used for a manual titration for alkalinity. Each would still require a graduated burette filled with an acid to determine the amount of acid to reach the pH end point.

 

 

 

pH Electrodes

A wide range of pH electrodes are available for measuring pH. The pH electrodes include ones supplied with our mini-trators for alkalinity of water and others include versions made specifically for non-aqueous titrations.

The probes designed for non-aqueous titrations are made with chemically resistant materials to withstand harsh chemicals. They also use a double junction design that allows the electrolyte to be replaced for example with lithium chloride dissolved in the solvent that is in the sample matrix.

 

 

Solutions

Solutions required for performing alkalinity titrations include calibration buffers and maintenance solutions used for cleaning and storage.

Calibration Solutions

The quality of a titration is only is as good as the calibration of the meter. A wide variety of calibration buffers are available including pH 8.20 that is used with our mini-titrators. The pH 8.20 buffer can be used with other meters as long as the value can be entered as a buffer. Many portable and benchtop meters allow for a custom calibration point such as pH 8.20

 

 

Benchtop Photometers and Spectrophotometers

Benchtop photometers are multi-parameter photometers for water treatment, wastewater treatment, aquaculture, and pools and spas. Each benchtop photometer has the methods specific to the industry pre-programmed into the meter. Spectrophotometers, like benchtop photometers, have pre-programmed methods for alkalinity but also allow users to develop custom methods.

 

 

Checker HC

A Checker HC, like a chemical test kit, are reagent based design with a color change to indicate the endpoint. The handheld colorimeters use the Beer-Lambert principle to determine the color change. The color change is measured by a photoelectric cell which is more accurate than subjective visual interpretation. Checker HC for alkalinity include those for marine use and display results in mg/L CaCO3 or dKh.

 

 

Chemical Test Kits

A variety of chemical test kits are available for measuring alkalinity from single parameter test kits to multi-parameter test kits for water quality, environment monitoring, and boilers and cooling towers.

 

 

 

Accessories

Accessories include magnetic stirrers that should be used while performing a manual titration to ensure adequate mixing and solution homogeneity. Other accessories include syringe and tubing for titration systems.

 

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