Method F-018G The Determination of Lithium in Greases
This method is suitable for the determination of lithium in
conventional soap thickened greases. It may be used for both new and
used samples but with less accuracy in the latter case.
Equipment Required:
Sherwood Flame photometer
Accurate balance weighing to +/-0.0005g
Muffle furnace
Platinum crucible
Reagents Required:
Sherwood lithium standard (1000 ppm)
Hydrochloric acid (cone.)
Sherwood lithium blank diluent
Method:
Weigh accurately about 1 gm of grease in a platinum crucible.
Ignite by gentle heating over a Bunsen. When all volatile matter has burned off, transfer to a muffle furnace at 550°C and heat until all carbon is removed.
Allow to cool, cover the crucible with a watch glass. Add carefully 2 ml concentrated HCI, using the watch glass to retain splashes.
When the reaction has ceased wash splashes from watch glass into the crucible with a little deionised water and heat to dryness on a water bath.
Dilute (quantitatively) the sample with Sherwood lithium blank until the expected concentration falls within the 0-10 ppm range.
From the stock lithium standard prepare 10, 7.5, 5 and 2.5 ppm standards using Sherwood lithium blank as diluent.
Aspirate the standards into the flame photometer and plot a calibration curve of intensity vs concentration.
Aspirate the unknown solution into the flame and record the intensity value.
Interpolate the sample lithium concentration from the standard curve.
Adjust the sample concentration by taking account of the dilution ratio.
NOTE: If the sample contains significant concentrations of other cations then prepare
standard solutions containing similar concentrations of these elements.
