HPLC Coupled with Quadrupole Mass Spectrometry in the Forensic Analysis of Cocaine

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Analysis of Cocaine Important for forensic analysis of crime scenes Samples are often found in the form of: An unknown powder (could contain other components) A human specimen Fluids (urine, blood saliva) Hair

Molecular structure of cocaine (C17H21NO4) with a molecular weight of 303.353 g/mol

Reverse Phase High Performance Liquid Chromatography (HPLC) Sample injected using pressurized system Compounds travel through column at different rate Interact with stationary phase Detection Traditionally by UV absorption More recently Mass spectrometry Better identification of unknowns In reverse phase HPLC: Stationary Phase: small silica particles with long hydrocarbons chains attached (non polar) Mobile Phase: solvent, typically a water/alcohol solution (polar)

HPLC Column with silica beads composing the stationary phase Typical Silica Bead with hydrocarbon chains

Typical HPLC Results: Red compound is less polar and present in lower quantity than the blue compound

Results in Cocaine HPLC


HPLC Results for Cocaine.  Peak for cocaine circled in red.

Mass Spectrometry

Quadrupole Mass Spectrometry Apply voltages to 4 parallel rods Create an electric field Can change voltages to scan through m/z ratios Resonant ions will make it through to the detector Non-resonant ions will be neutralized by hitting rod Quadrupole MS allows distinction of compounds with similar m/z Compounds can also be distinguished by fragmentation patterns Tandem mass spec (MS/MS) detect molecular ion add energy to fragment detect fragment ions

Diagram of Quadrupole Structure.  Distinguishing features and path of ions illustrated.

Example MS Results

Mass Spectrometry Results for Cocaine.  Unfragmented circled in bold red;
two resulting fragments of most common fragmentation circled in red.