Glass sample cells should be used when measuring in the low range mode, and plastic cells should be used when measuring in the high range mode. If using the Pocket Colorimeter II for pH and Chlorine, use the glass sample cells when measuring pH and the plastic cells when measuring chlorine.

The plastic cells have a shorter path length, and the calibration is different when glass vs. plastic cells are used. If a glass cell is used for a range that is calibrated with a plastic sample cell, the readings will be erroneously high.

Note that the plastic cell used with older model Pocket Colorimeters will not fit correctly in the Pocket Colorimeter II.

How do I dilute the primary Chlorine Standard Solution to prepare calibration standards for calibrating my Pocket II Colorimeter for Chlorine?

If you are required to calibrate your Pocket II Colorimeter, you will need to prepare several (typically 5 to 7) primary calibration standards at different concentrations. The calibration standards should span the full concentration range of the test you use. For example, if you use a Hach method that measures from 0 - 2.00 mg/L, prepare calibration standard concentrations that span this range, for example 0.3, 0.6, 0.9, 1.2, 1.6, and 1.9 mg/L Cl2.

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 (actual concentration on label)
• Flasks, volumetric, class A, glass, 200-mL
• Pipets, volumetric, class A, glass, 1, 2, 3, 4, 5, and 6 mL
• Pipet Filler
• Deionized water

Diluting the Chlorine Standard Solution:

1. Fill a 200-mL volumetric flask approximately half full with deionized water.

2. Open a chlorine standard solution ampule.

3. Pipet 1 mL of the chlorine standard solution into the flask.

4. 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.)

5. 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. You will find the actual concentration 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. 

Diluted concentration = chlorine ampule concentration x multiplier

Example: Your chlorine standard solution is 63.1 mg/L. You pipetted one mL of this standard into a 200-mL flask and diluted to the mark. The concentration of your 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.

The Pocket Colorimeter II Holster, is a carrying case made from durable fabric. Place your instrument, sample vials, and reagents in the holster. Then place the holster on your belt for convenience when taking field measurements.