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NAME THAT SUBSTANCE MDMAHeroin CocaineMeth MDMA heroin cocaine Baking soda and powder
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Chromatography Separation of Mixtures
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What Is Chromatography? A family of laboratory techniques for separating mixtures into their component compounds Uses some version of a technique in which two phases, one mobile, one stationary, flow past one another The mixture separates as it interacts with the two phases
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Basic Principle Different compounds will stick to a solid surface with different degrees of strength or vary in the efficiency with which they dissolve in a liquid
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Basic Principles A mobile phase sweeps the sample over a stationary phase – like the wind sweeps the swarm over the flower bed
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Basic Principles When a mixture of compounds flows over a surface, the molecules will stick to the surface If a molecule does not stick to the surface too strongly, the molecule stick & unstick many times as it is swept along the surface Over time, the molecules will become physically separated from each other
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Basic Principles When the molecules reach the far end of the surface, they are detected or measured one at a time as they emerge Chromatography is non-destructive – does not alter the molecular structure of the compounds
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Types of Chromatographic Attraction Adsorption Chromatography – depends on physical forces such as dipole attraction to cause the molecules to “stick” to the stationary phase column, TLC, HPLC
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Types of Chromatographic Attraction Partition Chromatography – depends on the relative solubility of the mixture’s molecules in the stationary phase coating – polarity may also have some effect gas chromatography
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Types of Chromatographic Attraction Size-exclusion – the relative sizes of the molecules determine how fast the molecules move through the stationary phase – large molecules flow right through – small molecules spend time trapped in the pores of the stationary phase gel filtration chromatography
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Types of Chromatographic Attraction Ion-exchange – depends on the relative strength with which ions interact with an ionic resin – less strongly held ions are displaced by more strongly attaching ions – one kind of ion is exchanged for another ion exchange chromatography
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Gas Chromatography Stationary phase – a solid or very syrupy liquid lines a tube (column) silicone polymers (like Silly Putty) commonly used Mobile phase – an inert gas nitrogen helium
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Gas Chromatograph (GC)
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GC Columns A packed column A capillary column
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Schematic of a GC
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Retention Time
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The time between when the sample is injected & when it exits the column reaching the detector Tm is the time taken for the mobile phase to pass through the column
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Analysis Using the GC Retention time can be used as an identifying characteristic of a substance – retention times may not be unique – GC is not an absolute method of identification An extremely sensitive technique – area under a peak is proportional to the quantity of substance present – allows quantitation of sample
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Identification of Accelerants unevaporated gasoline 90% evaporated gasoline unevaporated kerosene 90% evaporated kerosene
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Pyrolysis Gas Chromatography Used when sample does not readily dissolve in a solvent If heating such sample at high temp (500- 1000 0 C) decomposes it into gaseous products, the products can be analyzed by CGC A pyrogram is obtained
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Next Step? Now that you know WHAT is in there (qualitative), what do you want to know next?
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Mass Spectrometer (MS)
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Mass Spectrometer
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Mass Spectrum
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