ASTM D4629 Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons
ASTM D4629 Standard Test Method for Trace Nitrogen in Liquid Petroleum Hydrocarbons by Syringe/Inlet Oxidative Combustion and Chemiluminescence Detection
11. Procedure
11.1 Obtain a test specimen using the procedure in Section 8. The nitrogen concentration in the test specimen must be less than the concentration of the highest standard used in the calibration. Injection volumes ranging from 3 to 100 µL are acceptable depending on the instrument being used. The size of the injected sample shall be similar to the size of the injected standards used for calibration.
11.2 Flush a clean microlitre syringe several times with the sample to be determined, and introduce it into the furnace using the procedure outlines in 10.2-10.4 (depending on whether a boat inlet system is being used). For samples with total nitrogen concentration in the range 1 to 100 mg/kg, sample sizes injected are typically up to 10 µL. For samples with total nitrogen concentration less than 1 mg/kg, injected sample size can be up to 100 µL. Follow the instrument manufacturer's recommendation on sample size based on type of sample and level of nitrogen present.
11.3 To obtain one result, measure each test specimen a minimum of three times and calculate the average detector response.
12. Calculation
12.1 For samples introduced volumetrically (10.2.1 or 10.2.2), density values used for calculations are to be measured using Practice D1298, Test Method D4052 or their equivalent, at ambient temperature.
12.2 Calculate the nitrogen content of the sample in mg/kg for the average of the three determinations that make up a single result as follows:
nitrogen, mg/kg = (I - I0) x K/(S x V x D)
or
nitrogen, mg/kg = (I - I0) x K/(S x M)
where:
D = density of sample, g/mL,
S = slope of the calibration curve, counts/ng N,
V = volume of sample, µL,
K = dilution factor,
M = mass of sample, mg,
I = average detector response, integration counts, and
I0 = intercept of the calibration curve, integration counts.
12.3 For analyzers equipped with a calibration adjust, calculate the nitrogen content of the sample in mg/kg as follows (the average of three determinations make up a single result):
nitrogen, mg/kg = (I - B) x K/(V x D)
or
nitrogen, mg/kg = (I - B) x K/M
where:
D = density of sample, g/mL,
S = slope of the calibration curve, counts/ng N,
V = volume of sample, µL,
K = dilution factor,
M = mass of sample, mg,
I = visual display reading of the sample, ng N
B = average of visual display readings of the blank, ng N.
