ASTM D5184 Standard Test Methods for Determination of Aluminum and Silicon in Fuel Oils by Ashing, Fusion, Inductively Coupled Plasma Atomic Emission Spectrometry, and Atomic Absorption Spectrometry
9. Sampling
9.1 The objective of sampling is to obtain a sample for testing purposes that is representative of the entire quantity. Thus, take samples in accordance with the instructions in Practice D4057 or D4177. Typically, a gallon size container filled to approximately three-fourths of capacity is satisfactory.
10. Sample Handling
10.1 Homogenization - It is extremely important to homogenize the fuel oil in the sample container in order to obtain a representative specimen. (Warning - Failure to use this homogenization procedure can invalidate the results because non-representative aliquots could be obtained and this could lead to erroneous results.)
10.2 Place the sample container in an oven at a temperature of 50 to 60°C. Keep the container in the oven until the sample comes to temperature. Insert the shaft of a high speed homogenizer into the sample container so that the head of the shaft is immersed to approximately 5 mm from the bottom of the sample vessel. Mix the sample for about 5 min.
11. Specimen Preparation
11.1 Weigh a clean platinum dish to the nearest 0.1 g. Immediately transfer up to 50 g (but not less than 20 g) of the well-mixed sample, preferably containing about 1.3 mg aluminum, to the platinum dish and re-weigh the dish and contents to the nearest 0.1 g to obtain the weight of the specimen.
NOTE 3 - The specimen mass proposed, based on the aluminum content will suffice for silicon as both elements are usually found in fuel oils at similar concentrations.
11.2 Warm the dish and contents gently with a bunsen flame until the sample can be ignited. Maintain the contents of the basin at a temperature such that most of the combustible material is removed and only carbon and ash remain.
NOTE 4 - If the specimen contains considerable amounts of moisture, foaming and frothing can cause loss ofmaterial. If this is the case, discard the specimen and to a fresh portion add 1 to 2 mL of 2-propanol before heating. If this is not satisfactory, add 10 mL of a mixture of equal parts of toluene and 2-propanol and mix thoroughly. Place several strips of ashless filter paper in the mixture and warm gently. When the paper begins to burn, the greater part of the water will have been removed.
11.3 Place the dish and contents in a muffle furnace maintained at a temperature of 550 +/- 25°C. Maintain the muffle furnace at this temperature until all the carbon is removed and only ash remains. This may require more than 10 h in the muffle furnace and may conveniently be done overnight.
11.4 Cool the dish to room temperature, add 0.4 g of flux and mix with the ash. Place the dish in a muffle furnace maintained at a temperature of 925 +/- 25°C for 5 min. Remove the dish and ensure contact ofthe flux with the ash. Replace the dish in the muffle furnace and maintain at a temperature of 925 +/- 25°C for 10 min.
11.5 Remove the dish, cool the fusion melt to room temperature and add 50 mL of the tartaric acid/hydrochloric acid solution. Place the dish and contents on the hot plate maintained at a temperature of approximately 80°C. Heat until the melt is dissolved. (Warning - Vaporization of a significant amount of the liquid can lead to precipitation of an insoluble form of silica leading to erroneous results.)
NOTE 5 - Prolonged heating can be necessary to dissolve the melt completely and obtain a solution. Agitation or the use of magnetic stirring can be employed to speed dissolution of the melt.
11.6 Allow the solution to cool and then transfer it to a 100-mL flask with water, washing the dish several times to ensure transfer is complete. Make up to the mark with water. Then, transfer the solution to a plastic bottle.
NOTE 6 - Transferring the test solution to a plastic bottle is desirable because the dilute acid solution contains fluoboric acid from dissolution of the flux. Storage tests have shown that there is no significant attack of glassware in the short term (up to one week), and that the solution does not contain fluoride ion above the 5 mg/L concentration.
12. Preparation of Calibration Solutions
12.1 Blank Solution - Prepare a blank solution containing only 0.4 g flux and 50 mL ofthe tartaric acid/hydrochloric acid solution diluted to 100 mL. Transfer it to a plastic bottle.
12.2 Aluminum - Prepare a 250 mg/L aluminum working solution by diluting 25 mL of the 1000 mg/L standard solution to 100 mL with water. To each offour clean 100 mL volumetric flasks, add 0.4 g of flux and 50 mL of the tartaric acid/hydrochloric acid solution. To successive flasks add 2, 4, 10, and 20 mL of the 250 mg/L aluminum working solution and dilute to 100 mL with water. The calibration solutions contain 5, 10, 25, and 50 mg/L of aluminum, respectively.
12.3 Silicon - Prepare a 250 mg/L silicon working solution by diluting 25 mL of 1000 mg/L standard solution to 100 mL with water. To each of four clean 100 mL volumetric flasks, add 0.4 g of flux and 50 mL of the tartaric acid/hydrochloric acid solution. To successive flasks, add 2, 4, 10, and 20 mL of the 250 mg/L silicon working solution and dilute to 100 mL with water. These calibration solutions contain 5, 10, 25, and 50 mg/L of silicon, respectively.
12.4 Transfer all calibration standards to plastic bottles.
NOTE 7 - When both aluminum and silicon are being determined, the 5 to 50 mg/L calibration solutions can be combined providing there are no incompatibility problems caused by the reagents used in the preparation of the standard solutions described in 7.7.1 and 7.7.2.
