Alkalinity

Reagents

  • LaMotte total alkalinity indicator, Part # 7038-G (Amazon $12.94)

  • Baking soda

  • Distilled water

Prepare Calibration Solutions

  • Weigh out 12.63 g of baking soda. Add to 500 mL of distilled water. Mix until dissolved.

  • Dilute 100-fold to yield a 8.42 dKH (150 ppm CaCO3 equivalent) working stock.

  • Dilute the working stock as outlined in the Table below

Standard Curves

Method

  • To each 5 mL sample, add 5 drops of alkalinity solution. Cap and mix by inverting tube several times. An image of all of the calibration solutions after the reagents are added is shown above.

  • Transfer approx. 1mL of each calibration solution to a cuvette.

  • In the colorimeter plotting program, select the custom 610 nm LED and ppm as units. Calibrate the colorimeter with the 0 ppm alkalinity solution and measure absorbance of all of the solutions in duplicate.

Sample calibration data

  • To view/use: Download the file and open in the colorimeter plotting software as described here.