Can Hardness titration methods be used to accurately measure low levels of hardness?

Document ID

Document ID TE1089

Version

Version 5.0

Status

Status Published

Published Date

Published Date 07/10/2018
Question
Can Hardness titration methods be used to accurately measure low levels of hardness?
Summary
Low hardness methods for best accuracy
Answer
Hach method 8204 uses the digital titrator and either 0.0800 or 0.800 M EDTA titrant. The digital titrator accuracy of ±1% applies only to titrations requiring at least 100 digits. Using the lowest range of method 8204, 100 digits equates to 10 mg/L as CaCO 3 therefore, does not have a specified accuracy for hardness less than 10 mg/L as CaCO 3.

Method 8222 uses a buret and 0.010 M EDTA (0.020 N). The accuracy limitation of this method depends upon the accuracy of the buret. Typically 1 mL is the lowest volume of titrant that can be dispensed accurately, though some are able to accurately dispense less volume. Using the specified 0.0100 M titrant, the volume of titrant in milliliters is multiplied by 20 to achieve a result in mg/L as CaCO 3. Therefore this method is usually not very accurate when measuring hardness less than 20 mg/L as CaCO 3.

For an estimate of low level hardness use the Total Hardness Test Kit, Model HA-71A (catalog number 145201). It is a drop-count titration test kit with an estimated detection limit of 1 mg/L as CaCO 3. Each additional drop of titrant used equates to 1 mg/L as CaCO 3. Refer to the Hardness (Total) Test Kit Manual, Model HA-71A, Drop Count Titration Kit 1452-01 for detailed instructions.

For best accuracy of low-level hardness measured use Hach colorimetric methods 8374 or 8030. Dilute over-range samples to reach the detection limits of the test chosen. Method 8374 range: 8 to 1000 µg/L as CaCO 3 (0.008 to 1.000 mg/L) and method 8030 range: 0.05 to 4.00 mg/L as CaCO 3.

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