What are the guidelines for identifying which Total Chlorine application to use on an AT1000?

Document ID

Document ID TE10992

Published Date

Published Date 04/16/2019
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Question
What are the guidelines for identifying which Total Chlorine application to use on an AT1000?
Summary
Description of the different Total Chlorine applications included in the Amperometric Application pack to identify which applicaiton would be recommended to use.
Answer
The Titration Application Pack Amperometric: Free & Total Chlorine, Chlorine Dioxide, Chlorite, & Sulfite (Autocat) (Product # AP0007.AT1122) includes four different Total Chlorine applications.

"Tot. Cl2 0.005 to 1 mg_L" is recommended for samples in that range.
"Tot. Cl2 0.05 to 5 mg_L" is recommended for samples over 1 mg/L up to 5 mg/L.

These two applications are available for convenience for customers that have samples above 0.05 mg/L in addition to samples below 0.05 mg/L. For customers that only have samples above 0.05 mg/L colorimetric methods and instruments would be recommended over amperometric titration.

The other two applications are the applications where it can be less clear which one should be used.

The application "Tot. Cl2 0.005 to 0.100 mg_L" is the application that uses application note DOC316.52.93147_1ed_Total Chlorine Forward Titration 0.00564N Titrant, follows SM 4500-Cl D, and uses 0.00564N PAO (Product # 199953) as the titrant.

The application "Tot. Cl2 4500-E 3-100 ug_L" is the application that uses application note DOC316.52.93148_1ed_Total Chlorine Forward Titration Diluted Titrant, follows SM 4500-Cl E, and uses 0.000564N PAO (Product # 199849) as the titrant.

In theory the lower concentration titrant would be "better" for lower concentration samples, but this is based on older instrumentation and manual titrations from when the Standard Methods were developed. When using newer instrumentation like the AT1000 there is little difference in resolution, sensitivity, and reproducibility between the two applications. But using the lower concentration titrant does have some downsides over the higher concentration titrant. The consumable cost will increase as it will take 10x more titrant to reach the end point with the titrant that is 10x lower in concentration, and therefore the cost per test is increased. Also lower concentration titrant would be less stable as any offset in concentration would have a larger % error on result due to the lower relative concentration. (For example if the concentration was off by 0.0001, this would has a larger % error at 0.000564 than at 0.00564). Using the application that uses the dilute titrant requires the use of ACS grade KI for that reagent addition so the swifttester cannot be used for this reagent addition. (Although using the ACS grade KI over the swiftester is recommended for customers using the application with the higher concentration titrant is recommended as well when reading on samples closer to the detection limit.)

Because of these reasons using the application that uses 0.00564N PAO is recommended for almost all customers over the use of the dilute titrant. The alternate method (using 0.000564N PAO) is available specifically for customers who are required by regulation to follow SM 4500-Cl E (instead of D) which specifies the use of the lower concentration titrant.

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