Why do different Pocket Colorimeters for Chlorine give different results?

Document ID

Document ID TE492

Published Date

Published Date 06/13/2022
Question
Why do different Pocket Colorimeters for Chlorine give different results?
Summary
Pocket Colorimeter results on different models
Answer
There are three different Chlorine ranges available on a Pocket colorimeters.

Low range (LR):
Chlorine, Free and Total, Chlorine, Free and Total, Low Range, DPD Method 8021 (free)/8167 (total), AccuVac Ampuls, DR300 and Pocket Colorimeter II_DOC316.53.01450Range, DPD Method 8021 (free)/8167 (total), AccuVac Ampuls, DR300 and Pocket Colorimeter II
Mid range (MR):
Chlorine, Free and Total, Mid-Range, DPD Method 10245 (free)/10250 (total), Powder Pillows, DR300 and Pocket Colorimeter II_DOC316.53.01451
High range (HR):
Chlorine, Free and Total, High Range, DPD Method, Powder Pillows, DR300 and Pocket Colorimeter II_DOC316.53.01449 (Using 10 mL pillows)
Chlorine, Free and Total, High Range, DPD Method 10069 (free)/10070 (total), Powder Pillows, DR300 and Pocket Colorimeter II_DOC316.53.01490 (Using 25 mL pillows)

There are three different DR300s that can measure Chlorine:
DR300 Pocket Colorimeter, Chlorine, Free + Total, with Box Product # LPV445.97.00110 - This instrument can test for LR and HR with 10 mL pillows (PCII equivalent Product # 5870000)
DR300 Pocket Colorimeter, Chlorine, Free + Total, MR, with Box Product # LPV445.97.62110 - This instrument can test for MR and HR with 25 mL pillows (PCII equivalent Product # 5870062)
DR300 Pocket Colorimeter, Chlorine & pH, with Box Product # LPV445.97.12110 - This instrument can only test for HR w/ 25 mL pillows (PCII equivalent Product # 5870012)

In almost all circumstances the reason that two Pocket Colorimeters give a different result on the same sample is because the two instruments are set to use a different ranges. The different ranges have differences in the test procedure. So if two different instruments are set to a different range, but the same procedure is being followed, then the results will be different.

Here are some additional articles for more information:
Which range/sample cells should be used on the low range/high range DR300 for chlorine?
Why do the high range Chlorine methods use a 25 mL powder pillow with a 5 mL sample volume?
 

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