Method F-012G The Determination of Sodium in Raw Pine Oil

It involves conversion of the sample into an inorganic residue by ashing. The residue dissolved in sulphuric acid is diluted with distilled water, and sodium is determined using a Sherwood Flame Photometer.

Equipment Required:

1. Sherwood Flame Photometer
2. Small crucible (nickel or porcelain)
3. Bunsen burner, tripod, etc.
4. Accurate balance weighing to +/-O.0005g

Reagents:

• Anhydrous sodium sulphate (analar)
• Concentrated sulphuric acid
• Distilled water

Sample Preparation:

1. Weigh accurately 1g of raw pine oil into a small clean crucible.
2. Heat the sample under a bunsen burner in a fume cupboard. Ignite the vapours and ensure the sample burns freely. Re-ignition may be necesary before only a char remains.
3. Transfer the crucible to a muffle furnace pre-heated to 500-525C and maintain this temperature until all carbon is burned off.
4. Allow the crucible to cool and wash the ash off the sides with a little distilled water.
5. Add 1 ml of concentrated sulphuric acid to fully dissolve the ash.
6. Carefully add distilled water to the crucible and transfer the solution and washing to a 100ml volumetric flask.
7. Dilute to the mark using distilled water.

Standard Preparation:

Working Standard (5 ppm Na): Dilute 5ml of the stock standard to about 900mls with distilled water. Add 10ml of concentrated sulphuric acid and dilute to the mark with distilled water.

Prepare 3, 2 and 1 ppm Na standards by dilution of the working standard ensuring that each contains the equivalent of 1 ml concentrated H₂SO₄ per 100mls.

Method:

1. Aspirate the standards into the Sherwood Flame Photometer. Plot a standard curve of sodium concentration against the meter reading.
2. Aspirate the sample solution into the flame and record the meter reading.
3. From the graph read off the sample sodium concentration.
4. To calculate sodium concentration in mg/g of the raw pine oil divide the concentration read off the graph by 10.