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
5. Apparatus
5.1 Furnace - An electric furnace held at a temperature (1075 +/- 25°C) sufficient to pyrolyze all of the sample and oxidize sulfur to SO2.

5.2 Combustion Tube - A quartz combustion tube constructed to allow the direct injection of the sample into the heated oxidation zone of the furnace or constructed so that the inlet end of the tube is large enough to accommodate a quartz sample boat. The combustion tube must have side arms for the introduction of oxygen and carrier gas. The oxidation section shall be large enough (see Figs. 1 and 2) to ensure complete combustion of the sample. Figs. 1 and 2 depict conventional combustion tubes. Other configurations are acceptable if precision is not degraded.

5.3 Flow Control - The apparatus must be equipped with flow controllers capable of maintaining a constant supply of oxygen and carrier gas.

5.4 Drier Tube - The apparatus must be equipped with a mechanism for the removal of water vapor. The oxidation reaction produces water vapor which must be eliminated prior to measurement by the detector. This can be accomplished with a membrane drying tube, or a permeation dryer, that utilizes a selective capillary action for water removal.

5.5 UV Fluorescence Detector - A qualitative and quantitative detector capable of measuring light emitted from the fluorescence of sulfur dioxide by UV light.

5.6 Microlitre Syringe - A microlitre syringe capable of accurately delivering 5 to 20-µL quantities. The needle shall be 50 mm (+/-5 mm) long.

5.7 Sample Inlet System - Either of two types of sample inlet systems can be used.
5.7.1 Direct Injection - A direct injection inlet system must be capable of allowing the quantitative delivery of the material to be analyzed into an inlet carrier stream which directs the sample into the oxidation zone at a controlled and repeatable rate. A syringe drive mechanism which discharges the sample from the microlitre syringe at a rate of approximately 1 µL/s is required. See example, Fig. 3.

5.7.2 Boat Inlet System - An extended combustion tube provides a seal to the inlet of the oxidation area and is swept by a carrier gas. The system provides an area to position the sample carrying mechanism (boat) at a retracted position removed from the furnace. The boat drive mechanism will fully insert the boat into the hottest section of the furnace inlet. The sample boats and combustion tube are constructed of quartz. The combustion tube provides a cooling jacket for the area in which the retracted boat rests awaiting sample introduction from a microlitre syringe. A drive mechanism which advances and withdraws the sample boat into and out of the furnace at a controlled and repeatable rate is required. See example, Fig. 4.

5.8 Refrigerated Circulator - An adjustable apparatus capable of delivering a coolant material at a constant temperature as low as 4°C could be required when using the boat inlet injection method (optional).

5.9 Strip Chart Recorder, (optional).

5.10 Balance, with a precision of +/-0.01 mg (optional).

6. Reagents
6.1 Purity of Reagents - Reagent grade chemicals shall be used in tests. Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.

6.2 Inert Gas - Argon or helium only, high purity grade (that is, chromatography or zero grade), 99.998 % minimum purity, moisture 5 ppm w/w maximum.

6.3 Oxygen - High purity (that is, chromatography or zero grade), 99.75 % minimum purity, moisture 5 ppm w/w maximum, dried over molecular sieves. (Warning - Vigorously accelerates combustion.)

6.4 Toluene, Xylenes, Isooctane, reagent grade (other solvents similar to those occurring in samples to be analyzed are also acceptable). Correction for sulfur contribution from solvents (solvent blank) used in standard preparation and sample specimen dilution is required. Alternatively, use of a solvent with nondetectable level of sulfur contamination relative to the sulphur content in the sample unknown makes the blank correction unnecessary. (Warning - Flammable solvents.)

6.5 Dibenzothiophene, FW184.26, 17.399 % (m/m) S (Note 2).

6.6 Butyl Sulfide, FW146.29, 21.92 % (m/m) S (Note 2).

6.7 Thionaphthene (Benzothiophene), FW134.20, 23.90 % (m/m) S (Note 2).

NOTE 2 - A correction for chemical impurity can be required.

6.8 Quartz Wool.

6.9 Sulfur Stock Solution, 1000 µg S/mL - Prepare a stock solution by accurately weighing approximately 0.5748 g of dibenzothiophene or 0.4652 g of butyl sulfide or 0.4184 g of thionaphthene into a tared 100 mL volumetric flask. Dilute to volume with selected solvent. This stock can be further diluted to desired sulfur concentration (Notes 3-5).

NOTE 3 - Working standards should be remixed on a regular basis depending upon frequency of use and age. Typically, stock solutions have a useful life of about 3 months.

NOTE 4 - Calibration standards can be prepared and diluted on a mass/mass basis when result calculations are adjusted to accommodate them.

NOTE 5 - Calibration standards from commercial sources can be used if checked for accuracy and if precision is not degraded.

6.10 Quality Control (QC) Samples, preferably are portions of one or more liquid petroleum materials that are stable and representative of the samples of interest. These QC samples can be used to check the validity of the testing process as described in Section 14.