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Gambica

   

Method F-011G Sodium and Potassium in Silicates,Minerals and Ores

Equipment Required:

  1. Sherwood Model 410 Flame Photometer
  2. Accurate balance
  3. Platinum crucible
  4. Volumetric glassware.

Reagents:

  • 48% Hydrochloric acid
  • Concentrated Sulphuric acid (analytical quality)
  • Hydrochloric acid
  • Sodium standard 1000 ppm ( Sherwood part 00156620)
  • Potassium standard 1000 ppm ( Sherwood part 00156621)

Sample Preparation:

Transfer 1 gm of sample to 30ml platinum crucible, moisten the sample with about 5 drops of water and an equal volume of concentrated sulphuric acid and add 5 ml hydrofluoric acid.

Place the platinum dish in a porcelain dish. Heat the porcelain dish on a hot plate at a rate that will slowly evolve white fumes of sulphuric acid without boiling or splattering. When the sample is almost dry add a second portion of H2SO4 and HF and repeat the slow evaporation. Repeat a third time to make sure that the rock is completely decomposed. On the third evaporation take care to evaporate the sample to complete dryness driving off as much fluoride as possible. There is a tendency to splatter at this point and the heat must be carefully controlled. Use hot 1:9 HCI to transfer the metallic sulphates to a 250ml beaker. About 175mls of hot acid are sufficient with heating and stirring using a glass rod. Transfer the solution to a 200ml volumetric flask, cool and fill to the mark with 10% (V/V) hydrochloric acid. This provides a 0.5% solution of the rock sample in 10% (V/V) HCI.

Having prepared the sample in this way a further dilution may be necessary prior to presentation of sample to nebuliser.

Standard Preparation:

Prepare a series of sodium and potassium standards from the 1000 ppm Standards (10, 6, 4 and 2 ppm) ensuring that each standard contains the same concentration of HCI as the sample.

Method:

  1. Aspirate the 10 ppm standard and set the Coarse and Fine control to set the Display to 10.0
  2. Without touching the controls aspirate the other standards to check linearity.
  3. Aspirate the unknown solution and record the displayed Concentration in ppm

Calculation:

    Concentration of Na (or K) in % weight of original sample= Displayed value (ppm) x 200/ weight sample (gms ) x 10,000

12 September, 2008