ASTM D5453 for total sulfur in light hydrocarbons, motor fuels and motor oils
ASTM D5453 Standard Test Method for Determination of Total Sulfur in Light Hydrocarbons, Motor Fuels and Motor Oils by Ultraviolet Fluorescence
7. Hazards
7.1 High temperature is employed in this test method. Extra care must be exercised when using flammable materials near the oxidative pyrolysis furnace.
8. Sampling
8.1 Obtain a test unit in accordance with Practice D4057 or Practice D4177. To preserve volatile components which are in some samples, do not uncover samples any longer than necessary. Samples shall be analyzed as soon as possible after taking from bulk supplies to prevent loss of sulfur or contamination due to exposure or contact with sample container. (Warning - Samples that are collected at temperatures below room temperature can undergo expansion and rupture the container. For such samples, do not fill the container to the top; leave sufficient air space above the sample to allow room for expansion.)
8.2 If the test unit is not used immediately, then thoroughly mix in its container prior to taking a test specimen.
9. Preparation of Apparatus
9.1 Assemble and leak check apparatus according to manufacturer's instructions.
9.2 Adjust the apparatus, depending upon the method of sample introduction, to meet conditions described in Table 1.
9.3 Adjust the instrument sensitivity and baseline stability and perform instrument blanking procedures following manufacturer's guidelines.
10. Calibration and Standardization
10.1 Based on anticipated sulfur concentration, select one of the suggested curves outlined in Table 2. Carefully prepare a series of calibration standards accordingly. Make other volumetric dilutions of the stock solution to cover the various ranges of operation within these calibration curve guidelines. The number of standards used per curve can vary, if equivalent results are obtained.
10.2 Flush the microlitre syringe several times with the sample prior to analysis. If bubbles are present in the liquid column, flush the syringe and withdraw a new sample.
10.3 A sample size recommended for the curve selected from Table 2 must be quantitatively measured prior to injection into the combustion tube or delivery into the sample boat for analysis (Note 6 and Note 7). There are two alternative techniques available.
NOTE 6 - Injection of a constant or similar sample size for all materials analyzed in a selected operating range promotes consistent combustion conditions.
NOTE 7 - Injection of 10 µL of the 100 ng/µL standard would establish a calibration point equal to 1000 ng or 1.0 µg.
10.3.1 The volumetric measurement of the injected material can be obtained by filling the syringe to the selected level. Retract the plunger so that air is aspirated and the lower liquid meniscus falls on the 10 % scale mark and record the volume of liquid in the syringe. After injection, again retract the plunger so that the lower liquid meniscus falls on the 10 % scale mark and record the volume of liquid in the syringe. The difference between the two volume readings is the volume of sample injected (Note 8).
NOTE 8 - An automatic sampling and injection device can be used in place of the described manual injection procedure.
10.3.2 Fill the syringe as described in 10.3.1. Weigh the device before and after injection to determine the amount of sample injected. This procedure can provide greater accuracy than the volume delivery method, provided a balance with a precision of +/-0.01 mg is used.
10.4 Once the appropriate sample size has been measured into the microlitre syringe, promptly and quantitatively deliver the sample into the apparatus. Again, there are two alternative techniques available.
10.4.1 For direct injection, carefully insert the syringe into the inlet of the combustion tube and the syringe drive. Allow time for sample residues to be burned from the needle (Needle Blank). Once a stable baseline has reestablished, promptly start the analysis. Remove syringe once the apparatus has returned to a stable baseline.
10.4.2 For the boat inlet, quantitatively discharge the contents of the syringe into the boat containing quartz wool at a slow rate being careful to displace the last drop from the syringe needle. Remove the syringe and promptly start the analysis. The instrument baseline shall remain stable until the boat approaches the furnace and vaporization of the sample begins. Instrument baseline is to be reestablished before the boat has been completely withdrawn from the furnace (Note 9). Once the boat has reached its fully retracted position, allow at least 1 min for cooling before the next sample injection (Note 9).
NOTE 9 - Slowing boat speed or briefly pausing the boat in the furnace can be necessary to ensure complete sample combustion. Direct injection can ease sample handling and improve sample combustion characteristics for materials containing very volatile sulfur compounds.
10.4.3 The level of boat cooling required and the onset of sulfur detection following sample injection are directly related to the volatility of the materials analyzed. For volatile materials, effective cooling of the sample boat prior to sample injection is essential. The use of a refrigerated circulator to minimize the vaporization of the sample until the boat begins approaching the furnace or an increased time for boat cooling can be required.
10.5 Calibrate the instrument using one of the following two techniques.
10.5.1 Perform measurements for the calibration standards and blank using one of the procedures described in 10.2-10.4. Measure the calibration standards and blank three times. Subtract the average response of the blank injections from each calibration standard response. Then determine the average integrated response of each concentration (see 6.4). Construct a curve plotting of the average integrated detector response (y-axis) versus micrograms of sulfur injected (x-axis) (Note 10). This curve shall be linear and system performance must be checked each day of use. See Section 14.
NOTE 10 - Other calibration curve techniques can be used when accuracy and precision are not degraded.
10.5.2 If the apparatus features self calibration routine, measure the calibration standards and blank three times using one of the procedures described in 10.2-10.4. If blank correction is required and is not an available instrument option (see 6.4 or 10.5.1), calibrate the analyzer in accordance with manufacturer's instructions to yield results expressed as nanograms of sulfur (Note 10). This curve shall be linear and system performance must be checked with each day of use (see Section 14).
10.6 If analyzer calibration is performed using a different calibration curve than listed in Table 2, select an injection size based on the curve closest in concentration to the measured solution(s). Construct the calibration curve to yield values that can be used to report sulfur content on a mass/mass basis.
