Trouble identifying the correct CAS number for EDTA solutions

EDTACAStitrationreagentschemistry

Registration:
16.11.2022
Messages: 56

Luna_Star Topic author

28.03.2025 10:28

I am working on a titration protocol and need to ensure I am using the correct reagent grade of EDTA. I keep finding multiple CAS numbers listed for different forms, like disodium salt versus the free acid. Specifically, I need to know if the CAS number provided for the anhydrous form is the one I should be referencing when calculating molarity for a standard solution. Has anyone successfully used EDTA in complex matrix samples, and if so, what was the most reliable source for verifying its purity and associated CAS number? Any guidance on best practices for sourcing this reagent would be greatly appreciated.

15 Answers

10.02.2023
Posts: 128

UnrealGod

04.04.2025 09:00

Check the supplier's Certificate of Analysis (CoA). That's the gold standard for both purity and CAS verification.

26.11.2022
Posts: 392

Demon_C

23.05.2025 07:00

The CAS number changes depending on the counterion (Na2EDTA vs. H2EDTA). Always use the CAS number associated with the specific salt form you are weighing out.

31.12.2024
Posts: 240

Hudson_W

26.05.2025 15:20

For standardization, I highly recommend using a commercially prepared, certified EDTA titrant rather than trying to calculate it from anhydrous powder. It saves immense headaches regarding stoichiometry and purity.

05.09.2024
Posts: 1057

Burke_C

10.08.2025 08:49

If you are using the disodium salt, the CAS number is generally more stable for reporting purposes than the free acid form, especially in aqueous solution.

17.05.2022
Posts: 402

SystemRoot

15.08.2025 23:01

I found that referencing the IUPAC name alongside the CAS number is the most reliable way to avoid confusion between different hydrates or salts.

28.10.2023
Posts: 1050

DarkPhoenix

26.08.2025 18:43

Does anyone know if the CAS number for EDTA itself (the ligand) is different from the CAS number for the sodium salt?

30.06.2023
Posts: 338

IceQueen in response

03.09.2025 08:50

Re: The anhydrous form. You must confirm if the CAS number provided is for the pure ligand or for a specific derivative like the free acid. They are not interchangeable for accurate molarity calculation.

17.07.2024
Posts: 649

Teacher_C

16.11.2025 15:41

Always weigh the reagent in a controlled environment and use volumetric glassware calibrated for the specific temperature of your solution. Good technique matters as much as the CAS number.

22.07.2023
Posts: 279

SynthWave

30.11.2025 18:04

For complex matrices, I used a standard dip method and had to verify the EDTA purity using ICP-MS after the titration to account for potential metal contamination affecting the results.

05.06.2024
Posts: 138

Bishop_A in response

11.02.2026 03:33

I agree with the CoA suggestion. Never rely solely on general online databases for critical reagents like this. The CoA is specific to the batch and the supplier.

27.06.2023
Posts: 402

TechGuru

27.02.2026 22:30

If you are calculating molarity from the anhydrous powder, ensure your source specifies the exact molecular weight used for that specific CAS number, as hydration state changes the mass significantly.

27.02.2024
Posts: 1311

Uncle_C

01.03.2026 18:26

What about using EDTA chelate indicators? Does the indicator itself affect the effective CAS number calculation of the EDTA solution?

20.04.2022
Posts: 800

MacCready_M in response

10.03.2026 05:05

I had trouble too! I ended up calling the supplier directly and asking them to confirm the CAS number for the specific grade and counterion I needed. It was the only way to get a definitive answer.

25.03.2025
Posts: 300

Dillon_C

04.04.2026 02:36

For standardization, titrating against a primary standard like ZnSO4 or CaSO4 is much safer than trying to standardize the EDTA solution against another complexing agent.

14.05.2025
Posts: 146

WarzonePro

14.04.2026 21:23

The most reliable source I found was a specialized analytical chemistry textbook that cross-referenced CAS numbers with chemical structures, rather than just general chemical supplier sites. Good luck with your protocol!

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