Cobalt(II) thiocyanate
-thiocyanate-trihydrate-xtal-1976-CM-3D-balls.png)
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| Identifiers | |
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3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.019.234 |
| EC Number |
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PubChem CID
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CompTox Dashboard (EPA)
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| Properties | |
| C2CoN2S2 | |
| Molar mass | 175.098 g/mol |
| Hazards | |
| Safety data sheet (SDS) | External MSDS |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Cobalt(II) thiocyanate is an inorganic compound of cobalt.
It is best known for the cobalt thiocyanate test (or Scott test), which is a screening test for the presence of cocaine.
The test has been responsible for widespread false positives and false convictions. In Harris County, Texas, the prosecutor's office identified hundreds of false convictions, and is trying to notify those who were falsely convicted.[1][2]
Preparation
This compound may be prepared by the salt metathesis reaction of aqueous cobalt(II) sulfate and barium thiocyanate; barium sulfate precipitates, leaving the desired compound in solution:[3]
- CoSO4 (aq) + Ba(SCN)2 (aq) → BaSO4 (s) + Co(SCN)2 (aq)
Cobalt thiocyanate test
The cobalt thiocyanate reagent can be prepared by dissolving ten grams of cobalt (II) thiocyanate in a mixture of 490 milliliters of distilled water and 500 milliliters of glycerin.[citation needed]
The cobalt thiocyanate test is performed by placing approximately 2 to 4 milligrams of a target substance in a glass test tube, then 5 drops of cobalt thiocyanate reagent. After shaking, 1 or 2 drops of concentrated hydrochloric acid (other acids can be used[4]) are added, and the tube is again shaken. Ten drops of chloroform (or similar solvent)) are then added, and the tube is vortexed, then allowed to settle and separate into two layers. The final color of the chloroform (organic) layer is recorded.
Addition of the cobalt thiocyanate reagent to cocaine hydrochloride results in the surface of the particles turning a bright blue (faint blue for cocaine base). The solution changes back to pink upon adding one or two drops of hydrochloric acid and mixing. Addition of 10 drops of chloroform, vortexing, and allowing the solution to settle results in a blue organic layer for both cocaine hydrochloride and cocaine base.
Diphenhydramine and lidocaine also give blue organic layers. These compounds are known false positives for cocaine.
If the procedure is adjusted to basify the sample rather than acidifying it, the test can be used to test for ketamine hydrochloride.[5]
References
- ^ [https://www.propublica.org/article/common-roadside-drug-test-routinely-produces-false-positives Busted: Tens of thousands of people every year are sent to jail based on the results of a $2 roadside drug test. Widespread evidence shows that these tests routinely produce false positives. Why are police departments and prosecutors still using them?] by Ryan Gabrielson and Topher Sanders, ProPublica, July 7, 2016
- ^ ‘No Field Test is Fail Safe’: Meet the Chemist Behind Houston’s Police Drug Kits, Decades after L.J. Scott developed a test for cocaine, his invention played a role in hundreds of wrongful convictions in Houston, by Ryan Gabrielson, ProPublica, July 11, 2016
- ^ Cano, F. H.; García-Blanco, S.; Laverat, A. G. (1976). "The crystal structure of cobalt(II) thiocyanate trihydrate". Acta Crystallographica Section B. 32 (5): 1526. doi:10.1107/S0567740876005694.
- ^ Anna L. Deakin (2003). "A Study of Acids Used for the Acidified Cobalt Thiocyanate Test for Cocaine Base". Microgram Journal. 1: 40–43.
- ^ Morris, JA (2007-01-01). "Modified Cobalt Thiocyanate Presumptive Color Test for Ketamine Hydrochloride". J Forensic Sci. 52 (1): 84–87. doi:10.1111/j.1556-4029.2006.00331.x. PMID 17209915. Retrieved 2012-02-07.