ASTM D4927 Standard Test Methods for Elemental Analysis of Lubricant and Additive Components - Barium, Calcium, Phosphorus, Sulfur, and Zinc by Wavelength-Dispersive X-Ray Fluorescence Spectroscopy
TEST METHOD A (INTERNAL STANDARD PROCEDURE)
8. Reagents and Materials
8.1 Helium, for optical path of spectrometer.
8.2 P-10 Ionization Gas, 90 volume % argon and 10 volume % methane for the flow proportional counter.
8.3 Diluent Solvent, a suitable solvent free of metals, sulfur, and phosphorus (for example, kerosine, white oil, or xylenes).
8.4 Internal Standard Materials:
8.4.1 Nickel Octoate, preferably containing 5.0 more or less 0.1 mass % nickel. If the nickel concentration is higher or lower (minimum concentration that can be used is 2.5 more or less 0.1 mass % nickel), the laboratory needs to adjust the amount of sample taken in 9.1.1 to yield an equivalent nickel concentration level in the internal standard. Other nickel-containing organic matrices (free of other metals, sulfur, and phosphorus) may be substituted provided the nickel is stable in solution, the concentration is known (not less than 2.5 more or less 0.1 mass % nickel), and the laboratory can adjust the amount of sample taken in 9.1.1 to yield an equivalent nickel concentration level in the internal standard if the nickel concentration does not initially contain 5.0 more or less 0.1 mass % nickel.
NOTE 2 - Many X-ray tubes emit copper X rays which increase in intensity with age. This does not present a problem when using copper as an internal standard for zinc providing that frequent calibrations are performed. No problem exists when using nickel as internal for zinc and nickel is the preferred internal standard material.
8.4.2 Titanium 2-Ethylhexoide or Tin Octoate, preferably containing 8.0 more or less 0.1 mass % titanium or tin. If the titanium or tin concentration is higher or lower (minimum concentration that can be used is 4.0 more or less 0.1 mass % titanium or tin), the laboratory needs to adjust the amount of sample taken in 9.1.1 to yield an equivalent titanium or tin concentration level in the internal standard. Other titanium or tin containing organic matrices (free of other metals, sulfur, and phosphorus) may be substituted, provided the titanium or tin is stable in solution, the concentration is known (not less than 4.0 more or less 0.1 mass % titanium or tin), and the laboratory can adjust the amount of sample taken in 9.1.1 to yield an equivalent titanium or tin concentration level in the internal standard if the titanium or tin concentration does not initially contain 8.0 more or less 0.1 mass % titanium or tin.
8.4.3 Zirconium Octoate, preferably containing 12.0 more or less 0.1 mass % zirconium. If the laboratory uses zirconium octoate with a lower mass % zirconium concentration level, the laboratory needs to evaporate away the petroleum solvent to yield a solution that contains 12.0 more or less 0.1 mass % zirconium. Other zirconium containing organic matrices (free of other metals, sulfur, and phosphorus) may be substituted, provided the zirconium is stable in solution and the concentration is known and does not exceed 12.0 more or less 0.1 mass % zirconium. If the zirconium concentration is <12.0 more or less 0.1 mass %, the laboratory needs to evaporate away the petroleum solvent to yield a solution that contains 12.0 more or less 0.1 mass % zirconium.
8.4.4 Lead Naphthenate, containing 24.0 more or less 0.1 mass % lead.
8.5 Calibration Standard Materials:
NOTE 3 - In addition to calibration standards identified in 8.5.1-8.5.5, single-element or multielement calibration standards may also be prepared from materials similar to the samples being analyzed, provided the calibration standards to be used have previously been characterized by independent primary (for example, gravimetric or volumetric) analytical techniques to establish the elemental concentration mass % levels.
8.5.1 Barium 2-Ethylhexoide or Sulfonate, with concentrations not less than 4 mass % barium and certified to better than more or less 0.1% relative, so that calibration standards can be prepared as stated in 10.1.1 and 10.1.2.
8.5.2 Calcium Octoate or Sulfonate, with concentrations not less than 4 mass % calcium and certified to better than more or less 0.1 % relative, so that calibration standards can be prepared as stated in 10.1.1 and 10.1.2.
8.5.3 Bis(2-Ethylhexyl)Hydrogen Phosphate, 97 % purity (9.62 mass % phosphorus). Other phosphorus containing organic matrices (free of other metals) may be substituted provided the phosphorus is stable in solution and the concentration is not less than 4 mass % phosphorus and certified to better than more or less 0.1 % relative, so that calibration standards can be prepared as stated in 10.1.1 and 10.1.2.
8.5.4 Zinc Sulfonate or Octoate, with concentration not less than 4 mass % zinc and certified to better than more or less 0.1 % relative, so that calibration standards can be prepared as stated in 10.1.1 and 10.1.2.
8.5.5 Di-n-Butyl Sulfide, 97 % purity, (21.9 mass % sulfur). Other sulfur containing organic matrices (free of metals) may be substituted, provided the sulfur is stable in solution and the concentration is not less than 2 mass % sulfur and certified to better than more or less 0.1% relative, so that calibration standards can be prepared as stated in 10.1.2.
8.6 Quality Control (QC) Samples, preferably are portions of one or more lubricating oils or additives that are stable and representative of the samples of interest. These QC samples can be used to check the validity of the testing process and performance of the instrument as described in Section 12.
9. Preparation of Internal Standards
9.1 Barium, Calcium, Phosphorus, and Zinc:
9.1.1 Dispense 240 more or less 0.5 g of nickel octoate (5.0 more or less 0.1 mass % nickel), 30 more or less 0.1 g of titanium 2-ethylhexoide (8.0 more or less 0.1 mass % titanium) or 30 more or less 0.1 g of tin octoate (8.0 more or less 0.1 mass % tin), and 450 more or less 1 g of diluent solvent into a 1-L bottle. Shake or stir the bottle for a minimum of 10 min. If the laboratory uses internal materials that have different elemental concentrations than those explicitly stated in 8.4.1 and 8.4.2, it will be necessary for the laboratory to adjust the amount of sample taken in order to obtain an equivalent elemental concentration in the internal standard blend that is prepared according to the following equations:
A = 240 x (5/x)
B = 30 x (8/y)
C = 720 - [A + B]
where:
A = nickel containing material in blend, g,
B = titanium or tin containing material in blend, g,
C = diluent to add to blend, g,
x = nickel in material chosen as an internal standard, mass %, and
y = titanium or tin in material chosen as an internal standard, mass %.
9.2 Sulfur:
9.2.1 Lead Naphthenate (Warning - Hazardous. Lead naphthenate is toxic and precautions should be taken to avoid inhalation of vapors, ingestion, or skin contact.) 24 mass % lead, serves as a suitable internal standard. No further treatment of this compound is necessary.
10. Preparation of Calibration Standards
10.1 Barium, Calcium, Phosphorus, and Zinc:
10.1.1 For concentrations less than 0.1 mass %, prepare standards containing 0.00, 0.01, 0.025, 0.050, 0.075, and 0.10 mass % of each respective element in the diluent solvent.
10.1.2 For concentrations greater than 0.1 mass %, prepare standards containing 0.00, 0.10, 0.25, 0.50, 0.75, and 1.00 mass % of each respective element in the diluent solvent.
10.1.3 Dispense 1.000 more or less 0.001 g of the zirconium internal standard solution described in 7.4.3 into a 30-mL bottle. Prepare an individual bottle for each of the calibration standards.
10.1.4 Dispense 1.000 more or less 0.001 g of the internal standard solution described in 8.1.1 into a 30-mL bottle. Repeat for all of the calibration-standard bottles.
10.1.5 Add 8.00 more or less 0.001 g of each standard to a respective bottle containing the internal standards and shake or stir well (minimum of 10 min) to mix the constituents.
10.2 Sulfur:
10.2.1 Prepare five standards covering the range from 0.00 to 2.00 mass % sulfur in the diluent solvent.
10.2.2 Dispense 1.000 more or less 0.001 g of lead internal standard into 30-mL bottles (one bottle for each standard).
10.2.3 Add 9.000 more or less 0.001 g of each standard to each respective bottle containing internal standard. Shake or stir contents for a minimum of 10 min using apparatus defined in 6.2.
11. Instrument Calibration for Barium, Calcium, Phosphorus, Sulfur, and Zinc
11.1 Fill respective X-ray cups at least half full with the calibration standard solutions. Make sure that no wrinkles or bulges are present in the film. The film must be flat.
11.2 Place the sample cups in the X-ray beam in order to measure and record the net intensity (peak intensity - background intensity) for both the analyte signal and the internal standard signal according to the wavelengths and conditions suggested in Table 2. Up to 60-s counting periods may be used at each wavelength position. Do this for each of the calibration standards for each of the elements.
NOTE 4 - The parameters indicated in Table 2 are presented for guidance only and they will vary according to the instrument used.
11.3 Calculate the ratio, R, of the net element counts to their corresponding net internal standard counts for all of the net elements and standards as follows:
R = E/I
where:
E = net element counts, and
I = net internal standard counts.
NOTE 5 - Many modern X-ray spectrometer instruments will calculate this ratio automatically and store the information in the instrument computer system.
11.4 Perform regression analyses for each calibration element by ratioing the net element counts to the net internal standard counts versus the element concentration (mass %) on linear graph paper or by way of the instrument computer system. It is recommended that two separate regression analyses be performed for each calibration set for barium, calcium, phosphorus, and zinc, as defined in 10.1.1 and 10.1.2. The regression analyses will determine a slope and intercept for each calibration element that will be used to determine element concentrations of samples to be tested.
12. Analysis of Quality Control Samples
12.1 A QC sample shall be analyzed each day samples are analyzed to verify the testing procedure and instrument performance. Additional QC samples may be analyzed. The QC samples shall be treated as outlined in Section 13.
13. Procedure
13.1 Determination of Barium, Calcium, Phosphorus, and Zinc:
13.1.1 If the concentration of the element is known or suspected to be less than 1.0 mass %, dispense 8.000 more or less 0.001 g of the sample specimen into a 30-mL bottle containing 1.000 more or less 0.01 g of internal standard solution 9.1.1 and 1.000 more or less 0.001 of internal standard solution 8.1.2. Mix carefully using shaker for a minimum of 10 min.
13.1.2 If the concentration is known or found to be higher than 1.0 mass %, then dilute a sample specimen with the diluent solvent, such that the working concentration in the blend is reduced to approximately 0.5 mass %. Dispense 8.000 more or less 0.001 g of the diluted specimen into a 30-mL bottle containing 1.000 more or less 0.001 g of internal standard 9.1.1 and 1.000 more or less 0.001 g of internal standard 8.1.2. Mix carefully using shaker for a minimum of 10 min.
13.1.3 Pour a portion of sample from either 13.1.1 or 13.1.2 into a cell as described in 11.1 and obtain counts as described in 11.2. Calculate the ratio between the element and its internal standard as described in 11.3. Obtain the concentration of the element from the appropriate calibration curve. Undiluted sample results are to be reported directly.
NOTE 6 - In addition to calibration standards identified in 14.4.1-14.4.5, single-element or multielement calibration standards may also be prepared from materials similar to the samples being analyzed, provided the calibration standards to be used have previously been characterized by independent primary (for example, gravimetric or volumetric) analytical techniques to establish the elemental concentration mass % levels.
13.1.4 The mass % of barium, calcium, phosphorus, or zinc, or a combination thereof, is calculated as follows:
where:
M = concentration of the element from the calibration curve, mass %,
S = mass of sample specimen, g, and
D = mass of diluent solvent, g.
13.2 Determination of Sulfur:
13.2.1 If the sulfur content is known to be less than 2 mass %, transfer a 9.000 more or less 0.001-g sample specimen into a 30-mL bottle containing 1.000 more or less 0.001 g of the lead internal standard (9.2.1).
13.2.2 If the sulfur content is known or found to be higher than 2 mass %, dilute to approximately 1 to 1.5 mass % with the diluent solvent. Transfer 9.000 more or less 0.001 g of the diluted specimen into a 30-mL bottle containing 1.000 more or less 0.001 g of lead internal standard (9.2.1).
13.2.3 Run either 13.2.1 or 13.2.2 under the same conditions as the standards. Calculate the sulfur-to-lead ratio and obtain the sulfur concentration from the calibration curve. Undiluted sample results are reported directly. Refer to 13.1.4 for the calculation of diluted samples.