ASTM D7319 Standard Test Method for Determination of Existent and Potential Sulfate and Inorganic Chloride in Fuel Ethanol by Direct Injection Suppressed Ion Chromatography
11. Procedure
11.1 Obtain samples in accordance with Practice D4057 or Practice D4177. Samples should be well mixed to ensure homogeneity. Take a representative portion for analysis. Collect samples in containers with closures that seal well to prevent evaporation of ethanol. Samples containers should be clean and not contain any residual sulfate or chloride. If containers have been cleaned and rinsed with water, rinse them with water and dry them prior to use.
11.1.1 Thoroughly mix the samples in their containers immediately prior to withdrawal of a test specimen.
11.2 Set up the ion chromatograph in accordance with the manufacturer's instructions.
11.2.1 Equilibrate the system by pumping eluent for 15 to 30 min, until a stable baseline is obtained.
11.2.2 Start the ion chromatographic run in accordance with the manufacturer's instructions.
11.3 Existent Inorganic Sulfate and Total Chloride:
11.3.1 Obtain the denatured ethanol sample to be analyzed, no sample preparation is necessary.
11.3.2 The dilution factor Df equals 1.0, since the sample is not diluted.
11.3.3 Go to 11.6, if not analyzing for potential sulfate.
11.4 Potential Sulfate:
11.4.1 Add 9.5 mL of the denatured ethanol test specimen to a clean, dry, tared 10-mL glass volumetric cylinder.
11.4.2 Add 0.5 mL of 30% hydrogen peroxide solution to the sample (final concentration of 1.5% hydrogen peroxide), and shake it thoroughly for at least 30 s.
11.4.3 The dilution factor Df equals 1.05.
11.5 Inject 20 µL of sample solution from 11.3 or 11.4 into the ion chromatograph, and measure the areas of the peaks corresponding to chloride and sulfate ions.
11.6 Ifthe concentration ofthe anion ofinterest exceeds that of the highest calibration solution, dilute the sample solution with denatured ethanol containing no measurable sulfate or chloride as appropriate, and repeat the sample measurement. Take into account the dilution factor in the calculation of sulfate content in the ethanol sample, and calculate the dilution factor F as shown in Eq 5.
F = Vf/Vi
where:
F = the dilution factor,
Vi = the volume of the initial sample diluted, in mL, and
Vf = the volume of the final solution, in mL.
12. Calculation
12.1 Calculate the concentrations of sulfate or chloride in the ethanol sample as mg/L (µg/mL) as shown in Eq 6.
C = A x Rf x F x Df
where:
C = concentration of anion in the original ethanol sample, in mg/L,
A = anion peak area, from the ion chromatogram in 11.5, in counts,
Rf = calibration plot response factor from 11.6, in mg/L/counts,
F = dilution factor from Eq 5 (= 1.0 if no dilution), and
Df = dilution factor equals 1.0 for existent inorganic sulfate and total chloride from 11.3, 1.05 for potential sulfate from 11.4.
12.2 The units of mg/L (volume) can be converted to mg/kg (weight) using the density of the same denatured ethanol as is present in the sample, as in Eq 7. Denatured ethanol density can be measured using Test Method D4052.
Sulfate (mg/kg) = Sulfate (mg/L)/D
where:
D = Density of denatured ethanol, in g/mL for existent inorganic sulfate, or
D = Density of the ethanol/peroxide diluted sample, in g/mL for potential sulfate.
NOTE 6 - Any amount of water present in the ethanol samples will affect the sample density. Measurement of the sample density is necessary to achieve the most accurate results, especially in the case of the potential sulfate where the water content is approximately 5 % of the injected sample volume.
