Doctor test

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The doctor test or ( English ) doctor test is a qualitative method in analytical chemistry to detect hydrogen sulfide or mercaptans .

application areas

The doctor test is mainly used in the petrochemical and mining industries. It is also a mandatory alternative method for determining the sulfur mercaptan content in aviation fuels.

execution

The detection of hydrogen sulfide is carried out according to the Universal Oil Products method 41. The doctor's solution , which consists of an aqueous solution of lead oxide in sodium hydroxide, is added to the substance to be examined . A discoloration reaction occurs from a concentration of 0.5 ppmv hydrogen sulfide. A deep brown color is evidence of concentrations of more than 8 ppmv H 2 S. If the sample to be examined is in gaseous form, the hydrogen sulfide-containing gas is passed through a filter paper soaked with the doctor's solution.

If mercaptans are detected in fuels or solvents according to ISO 5275 or ASTM D4952, the sample is mixed with sodium plumbite Na 2 PbO 2 · 3H 2 O and shaken. Then a small amount of sulfur is added. The mixture is shaken further. The presence of mercaptans and / or hydrogen sulfide leads to a discoloration of the sulfur floating at the oil-water interface or to a discoloration of one of the two phases. Since this is a qualitative test, no conclusions can be drawn about the concentration of mercaptans.

standardization

The doctor test is a standardized verification procedure. It is described under

  • DIN ISO 5275: 2003: "Petroleum products and hydrocarbon solvents - Detection of thiols and other sulfur species - Doctor test",
  • ASTM D4952-09: "Standard Test Method for Qualitative Analysis for Active Sulfur Species in Fuels and Solvents (Doctor Test)" and
  • UOP 41-07: "Doctor Test for Petroleum Distillates".

literature

Individual evidence

  1. ↑ Glossary of Petroleum Industry Common Terms & Symbols
  2. ↑ Register of Mining Standards ( Memento of the original from September 12, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 268 kB), FABERG Mining Standards Committee, 10/2011.  @1@ 2Template: Webachiv / IABot / www.faberg.de
  3. ↑ ExxonMobil: World Jet Fuel Specifications 2005 (PDF; 841 kB) page 34; Accessed February 6, 2012.
  4. ↑ Patrick J. Moore, Rodney W. Spitler: HYDROGEN SULFIDE MEASUREMENT AND DETECTION. In: 2003 Proceedings. American School of Gas Measurement Technology, p. 119, accessed on July 14, 2016 (PDF; 109 kB).
  5. ^ RA Nadkarni: Guide to ASTM Test Methods for the Analysis of Petroleum Products and Lubricants , page 21, ASTM International, 2007, ISBN 978-0-8031-4274-9
  6. ↑ ISO 5275: 2003: Petroleum products and hydrocarbon solvents - Detection of thiols and other sulfur species - Doctor test
  7. ↑ ASTM D4952-09: Standard Test Method for Qualitative Analysis for Active Sulfur Species in Fuels and Solvents (Doctor Test)
  8. ↑ UOP41-07: Doctor Test for Petroleum Distillates