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 volumetric flask, and diluted to volume with dilute nitric acid (1.0% v/v). The LOD (limit of detection) for this method is given as 1.3 μg g-1 sodium and the LOQ (limit of quantitation) is 4.3 μg g-1 sodium.
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. Nebulize the working standard solutions and adjust the controls until steady zero and maximum readings are obtained. Nebulize 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.