Scott Test
Definition
A three-step cobalt thiocyanate presumptive test for cocaine and its salts. Step 1: cobalt thiocyanate reagent (blue in aqueous phase). Step 2: hydrochloric acid (blue disappears for non-cocaine compounds). Step 3: chloroform partition (cocaine-cobalt complex partitions as blue layer). All three steps must proceed correctly for a positive result.
- Test type
- Presumptive colour test for cocaine and its salts
- Primary reagent
- Cobalt thiocyanate solution
- Key indicator
- Blue precipitate in organic phase, with colour reversal in subsequent layers
- Steps required
- Three steps: cobalt thiocyanate, hydrochloric acid, chloroform partition
Common questions
What makes the Scott test specific to cocaine?+
The test uses cobalt thiocyanate reagent, which produces a distinct blue precipitate when it reacts with cocaine. The blue color then reverses in subsequent reagent layers (glycerine and saturated salt solution), confirming the result is genuine and not a false positive from other compounds.
Why does the Scott test use multiple steps instead of just one reagent?+
The three-step process eliminates false positives. Step 1 detects the initial blue reaction, Step 2 (hydrochloric acid) confirms the blue disappears for non-cocaine substances, and Step 3 (chloroform partition) verifies the cocaine-cobalt complex separates into a blue layer. All three must proceed correctly for a positive result, making the test more reliable than a single reaction.
Is the Scott test conclusive proof of cocaine?+
No. The Scott test is presumptive, meaning it suggests the presence of cocaine but requires confirmation with more definitive methods like gas chromatography or mass spectrometry. Other compounds can potentially interfere, which is why forensic labs always follow presumptive tests with instrumental analysis before making final conclusions.
Related terms
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- False Positive (Presumptive Test)
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Explained in these topics
- Presumptive Colour Tests: Marquis, Mecke, Duquenois-Levine, Cobalt Thiocyanate and ScottA three-step cobalt thiocyanate presumptive test for cocaine and its salts. Step 1: cobalt thiocyanate reagent (blue in aqueous phase). Step 2: hydrochloric ac...
- Stimulants: Cocaine, Amphetamines, Methamphetamine and MDMAA presumptive colour test specific for cocaine: cobalt thiocyanate solution gives a blue precipitate in the organic phase. Positive result in the first layer i...