ASTM D5708 Method for Nickel, Vanadium, and Iron in Crude Oils and Residual Fuels
ASTM D5708 Standard Test Methods for Determination of Nickel, Vanadium, and Iron in Crude Oils and Residual Fuels by Inductively Coupled Plasma (ICP) Atomic Emission Spectrometry
12. Apparatus
12.1 Refer to 7.1-7.4.

12.2 Sample Decomposition Apparatus (optional) - This apparatus is shown in Fig. 1. It consists of a high-silica or borosilicate 400-mL beaker for the specimen, an air bath (Fig.2) that rests on a hot plate, and a 250-watt infrared lamp supported 1 in. above the air bath. A variable transformer controls the voltage applied to the lamp.

12.3 Glassware, high-silica or borosilicate 400-mL beakers, volumetric flasks of various capacities, and pipettes of various capacities. When determining concentrations below 1 mg/kg, all glassware must be thoroughly cleaned and rinsed with water.

12.4 Electric Muffle Furnace, capable of maintaining 525 +/-25°C and sufficiently large to accommodate 400-mL beakers. The capability of an oxygen bleed is advantageous and optional.

12.5 Steam Bath (optional).

12.6 Temperature Controlled Hot Plate (optional).

13. Reagents
13.1 Aqueous Standard Solutions, individual aqueous standards with 1000 mg/L concentrations of vanadium, nickel, and iron.

13.2 Nitric Acid, concentrated nitric acid, HNO3.

13.3 Nitric Acid (1 + 1) - Carefully add, with stirring, one volume of concentrated nitric acid to one volume of water.

13.4 Dilute Nitric Acid (19 + 1) - Carefully add, with stirring, one volume of concentrated nitric acid to 19 volumes of water.

13.5 Sulfuric Acid, concentrated sulfuric acid, H2SO4.

14. Preparation of Standards and Quality Control (QC) Samples
14.1 Blank Standard - Dilute (19 + 1) nitric acid.

14.2 Multi-element Standard - Using the aqueous standard solutions, prepare a multi-element standard containing 100 mg/L each of vanadium, nickel, and iron.

14.3 Working Standard - Dilute the multi-element standard ten-fold with dilute nitric acid.

14.4 Check Standards - Prepare calibration check standards in the same way as the working standard and at analyte concentrations that are typical of the samples being analyzed.

14.5 Quality Control (QC) Samples - Follow Section 15 using the QC samples as test specimens.

15. Preparation of Test Specimens
15.1 Into a beaker, weigh an amount of sample estimated to contain between 0.0025 and 0.12 mg of each metal to be determined. A typical mass is 10 g. Add 0.5 mL of H2SO4 for each gram of sample.

NOTE 1 - If it is desirable to extend the lower concentration limits of the method, it is recommended that the decompositions be done in 10-g increments up to a maximum of 100 g. It is not necessary to destroy all the organic matter each time before adding additional amounts of sample and acid. When it is desirable to determine higher concentrations, reduce the sample size accordingly.

15.2 At the same time, prepare reagent blanks using the same amount of sulfuric acid as used for sample decomposition. Perform all steps specified in this section. (Warning - Reagent blanks are critical when determining concentrations below 1 mg/kg. To simplify the analysis, use the same volume of acid and the same dilutions as used for the samples. For example, if 20 g of sample is being decomposed, use 10 mL of sulfuric acid for the reagent blank.)

15.3 The use of the air bath apparatus (Fig. 2) to minimize sample spattering and foaming is optional. Place the beaker in the air bath, which is located in a hood. The hot plate is off at this time. Heat gently from the top with the infrared lamp (Fig.1) while stirring the specimen with a glass rod. As decomposition proceeds (indicated by a frothing and foaming), control the heat of the infrared lamp to maintain steady evolution of fumes. Give constant attention to each sample mixture until all risk of spattering and foaming is past. Then, gradually increase the temperatures of both the hot plate and lamp until the sample is reduced to a carbonaceous ash.

15.4 If the air bath apparatus is not used, heat the sample and acid on a temperature controlled hot plate. As described in 15.3, monitor the decomposition reaction and adjust the temperature of the hot plate accordingly. (Warning - Hot, fuming, concentrated sulfuric acid is a very strong oxidizing acid. The analyst should work in a well-ventilated hood and wear rubber gloves and a suitable face shield to protect against spattering acid.)

15.5 Place the sample in a muffle furnace maintained at 525 +/- 25°C. Optionally, introduce a gentle stream of oxygen into the furnace to expedite oxidation. Continue to heat until the carbon is completely removed.

15.6 Dissolve the inorganic residue by washing down the wall of the beaker with about 10 mL of 1 + 1 HNO3. Digest on a steam bath for 15 to 30 min. Transfer to a hot plate and gently evaporate to incipient dryness.

15.7 Wash down the wall of the beaker with about 10 mL of dilute nitric acid. Digest on the steam bath until all salts are dissolved. Allow to cool. Transfer quantitatively to a volumetric flask of suitable volume and make up to volume with dilute nitric acid. This is the specimen solution.

16. Preparation of Apparatus
16.1 Refer to 10.1-10.3.

17. Calibration and Analysis
17.1 Refer to Section 11.

17.2 Analyze the reagent blank (refer to 15.2) and correct the results obtained on the test specimen solutions by subtracting the reagent blank results.