Sulfate standards

Reagents

• SulfaVer® 4 Sulfate Reagent, 10 mL, Hach, Part # 2106769, $28.95 for 100 tests

• Sulfate standard, 1000 ppm, Labchem Part # LC255101, $33.20 for 500 mL

• Distilled water

Equipment

List of vendors and prices: https://sites.google.com/iorodeo.com/colorimeter/equipment

• Colorimeter with RGB board (use green for measurement)

• Cuvettes

• 1 x 50 mL capped tube

• 9 x 10 mL capped tubes

• Pippete pump

• 5 mL, 10 mL pipettes

Prepare calibration solutions

• Prepare a 375 ppm sulfate working standard: In a clean 50 mL tube, add 7.49 mL of 1,000 ppm sulfate standard + 12.51 mL of distilled water. Cap and mix.

• Dilute the 375 ppm sulfate standard as outlined in the Table below

Method

• To each 10 mL sample, add the contents of one SulfaVer 4 Sulfate reagent, shake and let stand. An image of all of the calibration solutions after adding the powder reagent is shown above.

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

• In the colorimeter plotting program, select the green LED and ppm as units. Calibrate the colorimeter with the 0 ppm sulfate solution and measure absorbance of all of the solutions in duplicate or triplicate.

Sample calibration data

• Sample calibration data: sulfate_hach.txt

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

• Calibration curve measurements were repeated three times. Data for the three separate calibration trials were compiled into one file. The final plot for all three sets of data is shown in the graph below