Determination of Sodium in Biodiesel using Dry Decomposition for the Sample Preparation
This method allows the analyte to be pre-concentrated in the final solution, decreases the volume of strong acid used in the dissolution stage and does not use organic solvents.
The sample of biodiesel is weighed into a crucible and placed in a heating muffle furnace.
Two temperatures are used in the heating program for the dry decomposition: the first temperature (250ºC) is maintained for 1 hour to dry the sample. After this the temperature is progressively elevated to 600ºC and maintained for 4 hours to eliminate the remaining organic material.
After cooling, the resulting inorganic residue is dissolved in a nitric acid solution (1.0% v/v). The resulting solution is transferred to a 100ml polypropylene volumetric flask, and diluted to volume with distilled water.
Due to sodium rapidly plating out onto glassware, polypropylene volumetric flasks should be used for the sample and standards, if not available the analysis of the sample should be carried out rapidly.
It should be noted that when following this method all standards should be diluted in the same 1.0% nitric acid solution to negate any spectral interferences caused by it being present in the solution when the sample is introduced to the flame photometer.
Preparation of Standard Graph
Set the flame photometer in accordance to MultiPoint/Single Ion Calibration found on page 24 of the BWB Technologies Installation and Operation Manual, to measure potassium emission. Nebulise the working standard solutions and adjust the controls until steady zero and maximum readings are obtained. Nebulise the intermediate working standard solutions and construct a graph relating raw emission data (known as RAW in BWB the flame photometer) to concentration of all the standard solutions.