ASTM D6667 Standard Test Method for Determination of Total Volatile Sulfur in Gaseous Hydrocarbons and Liquefied Petroleum Gases by Ultraviolet Fluorescence
11. Procedure
11.1 Obtain a test specimen using the procedure described in Section 8. Typically the sulfur concentration in the test specimen is less than the concentration of the highest standard and greater than the concentration of the lowest standard used in the calibration.
11.2 Measure the response for the test specimen using one of the procedures described in 10.2-10.4.
11.3 Inspect the combustion tube and other flow path components to verify complete oxidation of the test specimen. 11.3.1 Reduce the rate of injection or the sample size, or both, of the specimen into the furnace when coke or sooting is observed.
11.4 Cleaning and Re-calibration - Clean any coked or sooted parts according to the manufacturer's instructions. After any cleaning or adjustment, assemble and check the apparatus for leaks. Repeat instrument calibration prior to reanalysis of the test specimen.
11.5 To obtain one result, measure each test specimen three times and calculate the average detector response.
11.6 Density values needed for calculations are to be measured using Test Methods D1070 or equivalent, at the temperature at which the sample was tested (Note 8).
NOTE 8 - When sample matrix compositions are known, other techniques may be used to derive sample density, provided accuracy and precision are not degraded.
12. Calculation
12.1 For analyzers calibrated using an internal self-calibration, calculate the sulfur content in the test specimen as follows:
where:
d = density of standard mixture, g/mL,
s = density of sample, g/mL, and
G = sulfur found in test specimen, mg/kg.
12.2 For analyzers calibrated using a one point calibration, calculate the calibration factor, (10.5.2.4).
or
where:
Ac = integrated detector response for calibration standard, in counts, and
Mc = mass of calibration standard injected, in milligrams, either measured directly or calculated from measured volume injected and density.
Mc = V x Dc
where:
Dc = density of calibration standard at measurement temperature, g/mL,
Vc = volume of calibration standard injected, µL,
Scg = sulfur content of calibration standard, mL/kg, and
Scv = sulfur content of calibration standard, mg/L.
12.2.1 Calculate the average of the calibration factor (K) and check that the standard deviation is within the tolerance accepted. This calibration factor shall be established every day.
12.2.2 Calculate the sulfur content, S, of the sample, in mg/kg, using the following equation:
or
where:
K = calibration factor, in counts per nanogram of sulfur, and
M = mass of test specimen solution injected, in milligrams, either measured directly or calculated from measured volume injected and density.
M = V x D
where:
D = density of test specimen solution at measurement temperature, g/mL,
V = volume of the test specimen solution injected, µL,
A = integrated detector response for sample, in counts number,
Fg = gravimetric dilution factor, mass of test specimen/mass of test specimen and solvent, g/g, and
Fv = volumetric dilution factor, mass of test specimen/volume of test specimen and solvent, g/mL.