ABC Drug Analysis cheat sheet

Qualitative identification requires at least two independent analytical methods (e.g., color test plus GC-MS or FTIR) to establish identity.

Gas chromatography separates volatile analytes by boiling point and affinity for the stationary phase; retention time (not peak height) is the identification parameter.

Mass spectrometry detection (GC-MS) matches an electron-impact fragmentation pattern against a library; the molecular ion and base peak are key confirmatory features.

FTIR identifies compounds by absorption bands from molecular vibrations; a match requires all major peaks in the fingerprint region, not just one band.

Cocaine base (crack) is distinguished from cocaine HCl by solubility: base is insoluble in water and soluble in organic solvent; the salt dissolves in water.

Methamphetamine HCl is water-soluble; the free base is volatile and soluble in organic solvents, so solvent choice and pH drive extraction recovery.

Quantitation of seized drugs uses an internal standard with a calibration curve; report concentration with uncertainty and the analytical method used.

Presumptive color tests (e.g., cobalt thiocyanate for cocaine) are screening only and cannot support a positive identification alone.

Sampling plans for large seizures follow a hypergeometric or square-root model to estimate the probability that a sampled unit contains the analyte.

Chain of custody documents every transfer of evidence: who had it, when, and for what purpose; an unbroken record is required for admissibility.

The controlled-substance schedules (I–V) rank abuse potential and accepted medical use; Schedule I has high abuse potential and no accepted medical use.

Analytical balance calibration and verification are performed with certified weights traceable to a national standard before weighing evidence.

Limit of detection (LOD) is the lowest amount distinguishable from blank; limit of quantification (LOQ) is the lowest amount measurable with acceptable precision.

Specificity is the ability to measure the analyte without interference from matrix or structurally similar compounds; selectivity is the same concept applied to a group.

Measurement uncertainty combines Type A (statistical) and Type B (calibrated instrument, certificate) contributions, typically reported at 95% confidence.

A blank (negative control) and a positive control are run with each batch to detect contamination and confirm the method is performing.

Chromatographic resolution Rs = 2(t2 − t1)/(w1 + w2); baseline resolution is Rs ≥ 1.5.

Isomer discrimination (e.g., d- vs l-methamphetamine) requires chiral chromatography or a chiral derivatizing reagent.