Why does the Hach method for distillation with Fluoride differ from Standard Methods?

Document ID

Document ID TE4366

Version

Version 3.0

Status

Status Published

Published Date

Published Date 03/21/2019
Question
Why does the Hach method for distillation with Fluoride differ from Standard Methods?
Summary
Hach method for distillation with Fluoride differ from Standard Methods
Answer
Standard Methods instructs the user to distill the solution with 2:1 water to acid until it reaches a boiling point of 180C then discard the distillate. This creates the correct boiling point for addition of samples and distillation back to this boiling point.

From a table of sulfuric acid concentrations vs. boiling points, 180C corresponds to solutions of about 65-70% H2SO4. Hach's distillation is made by combining a 2:1 acid to water solution to create approximately a 67% acid solution to create the Standard Methods solution obtained after the initial distillation.

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