How do I dilute the primary chlorine standard solution to prepare calibration standards for calibrating my DR300 or Pocket Colorimeter™ II for chlorine?

Document ID

Document ID TE493

Published Date

Published Date 07/12/2021
How do I dilute the primary chlorine standard solution to prepare calibration standards for calibrating my DR300 or Pocket Colorimeter™ II for chlorine?
Prepare primary standards to calibrate DR300 or Pocket Colorimeter II for chlorine
The DR300 for chlorine (Product # LPV445.97.00110) and the Pocket Colorimeter™ II, Chlorine (Free and Total) (Product # 5870000) is factory calibrated and does not need to be user calibrated. However, the instrument does accept a user-prepared calibration curve, if the user chooses to do so.
In order to calibrate the colorimeter, several primary standards (typically 5 to 7) at different concentrations will need to be prepared. The calibration standards should span the full concentration range of the test. For example, if using a Hach method that measures from 0 - 2.00 mg/L, prepare calibration standard concentrations that span this range. For example, a good range to use would be 0.3, 0.6, 0.9, 1.2, 1.6, and 1.9 mg/L Cl 2.

The following procedure is one way to accurately prepare 6 chlorine calibration standards from a Hach Chlorine Standard Solution:

Required Items:
-Chlorine Standard Solution, 50-75 mg/L as Cl 2, pk/16 - 10 mL Voluette Ampules (NIST) (actual concentration on label) (Product # 1426810)
 -Flask, volumetric Class A, Glass, 200 mL (Product #1457445)
-Pipette, Variable Volume, 1.0 - 5.0 mL (Product # BBP065)
-Pipette  Tips for BBP065 (1.0 - 5.0 mL) 75/pk (Product # BBP068)
-Water, Deionized, 4 L (Product # 27256)

Diluting the Chlorine Standard Solution:
1. Fill a 200-mL volumetric flask approximately half full with deionized water. Open a chlorine standard solution ampule.
2. Pipet 1 mL of the chlorine standard solution into the flask.
3. Fill the flask to the mark with deionized water, stopper, and invert repeatedly to mix. This makes an approximately 0.3 mg/L Cl2 standard solution. (Use the equation below to find the exact concentration.)
4. Prepare additional standards by repeating the above steps, substituting 2, 3, 4, 5, and 6 mL of the chlorine standard solution for the 1 mL shown in step 3.

Calculating the Concentration: Because Chlorine Standard Solutions are difficult to prepare accurately, Hach targets a concentration range, in this case 50 to 75 mg/L, and then determines the actual concentration by amperometric titration. The actual concentration is on the label. Use this concentration to calculate each of your calibration standard concentrations. Multiply the concentration from the Chlorine Standard Solution label by the multipliers in the following table:

Standard #    Pipet volume (mL)    Multiplier
     1                         1                        0.005
     2                         2                        0.01
     3                         3                        0.015
     4                         4                        0.02
     5                         5                        0.025
     6                         6                        0.03 

Diluted concentration = chlorine ampule concentration x multiplier.

Example: the chlorine standard solution value is 63.1 mg/L. One mL was pipetted into a 200-mL flask and diluted to the mark. The concentration of the diluted standard is 63.1 x 0.005 = 0.32 mg/L chlorine. Enter 0.32 in the calibration mode of your Pocket II Colorimeter for standard 1. Measure the absorbance of this standard after adding the DPD reagent.

Note: Use the diluted standard solutions as soon as possible after mixing.

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