Which standard can be used to check TOC determination using the difference method in cell test LCK380/LCK381?

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Document ID TE10151

Published Date

Published Date 03/24/2020
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Question
Which standard can be used to check TOC determination using the difference method in cell test LCK380/LCK381?
Answer
Regulatory requirements for the TOC standard difference method

a) TOC stock solution with 1000 mg/L
2.125 g Potassium Hydrogen Phthalate (Merck 60359) in 1 L DI water.
The Potassium Hydrogen Phthalate must be dried at 105 °C for 2 h before weighing and then stored dry and airtight.
b) Dissolve TIC stock solution with 1000 mg/L
4.410 g Sodium Carbonate (Merck 106392) and 3.5 g Sodium Hydrogen Carbonate (Merck S6014) in 1 L DI water. Both substances must be dried using silica gel before weighing and then stored dry and airtight.
Caution!
The TIC solutions produce an alkaline reaction and adsorb CO 2 from the ambient air. Therefore, they must not be left open under any circumstances and must be freshly prepared for each test.
The shelf life of the TC stock solution is max. 2 weeks if refrigerated.

Standard LCK380 example:
Pipette 3 ml of TOC stock solution and 1.5 ml of TIC stock solution into a 100-ml flask and fill with DI water.
Target values:
TC: 45 mg/L
TIC: 15 mg/L
TOC: 30 mg/L

Standard LCK381 example:
Pipette 40 ml of TOC stock solution and 15 ml of TIC stock solution into a 100-ml flask and fill with DI water.
Target values:
TC: 550 mg/L
TIC: 150 mg/L
TOC: 400 mg/L

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