ISO 20846 Petroleum products - Determination of sulfur content of automotive fuels - Ultraviolet fuorescence method
WARNING - The use of this International Standard may involve hazardous materials, operations and equipment. This International Standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this International Standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

1 Scope
This International Standard specifes an ultraviolet (UV) fuorescence test method for the determination of the sulfur content of motor gasolines containing up to 3.7 % (m/m) oxygen [including those blended with ethanol up to about 10 % (V/V)], and of diesel fuels, including those containing up to about 10 % (V/V) fatty acid methylester (FAME), having sulfur contents in the range 3 mg/kg to 500 mg/kg. Other products can be analysed and other sulfur contents can be determined according to this test method, however, no precision data for products other than automotive fuels and for results outside the specifed range have been established for this International Standard. Halogens interfere with this detection technique at concentrations above approximately 3500 mg/kg.

NOTE 1 Some process catalysts used in petroleum and chemical refning can be poisoned when trace amounts of sulfur-bearing materials are contained in the feedstocks.

NOTE 2 This test method can be used to determine sulfur in process feeds and can also be used to control sulfur in effuents.

NOTE 3 For the purposes of this International Standard, the terms "% (m/m)" and "% (V/V)" are used to represent the mass fraction and the volume fraction of a material respectively.

NOTE 4 Sulfate species in ethanol do not have the same conversion factor of organic sulfur in ethanol. Nevertheless, sulfates have a conversion factor close to that of organic sulfur.

NOTE 5 It is preferable to check the nitrogen interference and to take it into account, especially when sulfur content is measured on diesel blended with cetane improver containing nitrogen. For example, alkyl nitrate, as 2-ethyl hexyl nitrate (EHN), added as cetane improver to diesel fuel shows an enhancing effect on sulfur content that can range from 0 to 1.7 mg/kg when 2000 mg/kg EHN is added to diesel fuel containing 10 mg/kg sulfur.

2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 1042, Laboratory glassware - One-mark volumetric fasks
ISO 3170, Petroleum liquids - Manual sampling
ISO 3171, Petroleum liquids - Automatic pipeline sampling
ISO 3675, Crude petroleum and liquid petroleum products - Laboratory determination of density - Hydrometer method
ISO 12185, Crude petroleum and petroleum products - Determination of density - Oscillating U-tube method

3 Principle
A hydrocarbon sample is injected into a UV fuorescence detector. The sample enters a high temperature combustion tube (1000 °C to 1100 °C), where the sulfur is oxidized to sulfur dioxide (SO2) in an oxygen-rich atmosphere. Water produced during the sample combustion is removed and the sample combustion gases are exposed to UV light. The SO2 absorbs the energy from the UV light and is converted to excited sulfur dioxide (SO2*). The fuorescence emitted from the excited SO2* as it returns to a stable state SO2 is detected by a photomultiplier tube and the resulting signal is a measure of the sulfur contained in the sample.