Moisture content of tall oil by coulometry

PCTM 4B

ISSUED- 1996

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Moisture content of tall oil by coulometry

Scope

This test method covers the determination of water in liquid organic materials containing <2% water. The moisture content of tall oil is determined by automatic titration with coulometrically generated Karl Fisher reagent In the Karl Fisher reaction, iodine reacts with water in the presence of sulfur dioxide, an organic nitrogen base like pyridine and an alcohol:

I2+ H2O + SO2+ ROH + 3RN→2RN•H1+ RN•HSO4R

With coulomettic titrators the required iodine is produced by anodic oxidation of an iodide contained in the cell reagents. The sample water content is then determined directly by electronically integrating the current required to generate sufficient iodine to precisely react with the water in the sample.

Safety precautions

Always operate the titrator in a fume hood. Most of the reagents, including some of the pyridine-free systems are noxious or toxic and inhalation or direct skin contact with them should be avoided.

Apparatus

1. Coulometric Karl Fisher titrator.

2. Sample vials, 8-nt or 4-dram.

3. Medicine droppers.

4. Disposable plastic syringes, 1-cc with 16, 18 or 20 gauge needles.

5. Syringe, 10-uL.

Reagents

Karl Fischer pyridine-free reagent. Reagents are available from the manufacturer of the apparatus.

Instrument preparation

Prior to sample analysis the analyst must become familiar with the operation of the titrator which differs slightly depending on the manufacturer of the apparatus.

1.Prepare and calibrate the apparatus as specified in the operating manual supplied by the manufacturer. This generally includes the following step

a. Clean and assemble the titration chamber.

b.Pour the titration solution into the chamber.

c.Add the iodine generator solution to the generator assembly.

d.Put the instrument in STANDBY position.

e.Slowly add neutralizing solution normally by injection with a syringe)

f.Continue the addition until the instrument indicates by a light or a message on an LCD that excess water is present.

g.Stop the addition of neutralizing solution.

h.Let the instrument stabilize for 1 hour in the STANDBY position.

2. Verify the instrument by injecting a known amount of water, usually 1 uL to 5 uL below the surface of the titration solution.

3. Put the instrument in the TITRATE or RUN position and record the reading when the END light comes on or a message appears that the titration is complete.

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