Forensic Analysis of Drugs

Forensic drug analysis deals with the identification and quantification of illegal drugs. Forensic drug test are generally carried out in two steps – screening and confirmation. Once drugs are detected through screening, for example spot test kits (e.g., immunoassays, Marquis test, etc), samples are then collected and sent to laboratories for confirmation tests. Confirmation requires high sensitivity and selectivity toward drugs, as well as their metabolites, and is frequently carried out by GC/MS.

Following are the screening and confirmatory tests which are
normally performed.

Color Tests/Spot Tests

Many drugs yield characteristic colors when they are allowed to react with certain specific chemical reagents. These tests not only indicate the presence of certain drug but also are for screening purposes to give the investigator a proper direction in which he/she can proceed his investigation. When conducting a color test, chemicals known to produce a colored product in the presence of a suspected drug are added to a small amount of the questioned sample. If the questioned sample contains the suspected drug, a colored product, having a color representative of the suspected drug, will be produced. Color test reactions are generally performed in crime
laboratories using spot plates.

Different chemicals are used for each drug to be tested. Some chemicals, however, are used for more than one class of drugs. For example, the Marquis test, consisting of two chemicals (Concentrated sulphuric acid and formaldehyde) yields a purple product for opiates like morphine, heroin, codeine, and oxycodone and an orange-red product for amphetamine and methamphetamine.

Following is a table of a few reagents which are generally used in drug screening-

Test	Chemical	Test Result	Positive
Van Urk Test	P-dimethylaminobenzaldehyde in 10% concentrated HCI and ethanol	Purple	LSD
Marquis Test	2% Formaldehyde in Sulphuric Acid	Brown Orange Purple	Amphetamine Opium
Simon’s Test	Sodium nitroprusside and Na2CO3	Deep Blue	Methamphetamine
Dillie-Koppanyi Test	1% cobalt acetate in CH3OH followed by 5% isopropylamine in CH3OH	Violet	Barbiturates
Scott Test	Cobalt thiocynate, HCI, glycerine and chloroform	Blue	Cocaine
Duquenois- Levine Test	Tetrahydrocannabinol (THC)	Purple	Marijuana

Microcrystal Tests

Microcrystal tests are more specific than color tests. In these tests, different reagents are made to react the drug, producing a crystalline precipitate. It is the size and shape of the crystal, under microscopic examination, which are highly characteristic of drug.

However, these tests are also not confirmatory, so the presence of a certain drug needs to be further confirmed by various sophisticated instruments.

Drug	Reagents	Colour
Heroine	Platinum Chloride	Rosette
Morphine	Potassium Chromate	Small plates
Nicotine	Sodium Carbonate	Rosette and bunches of needles
Papaverine	Platinum Chloride	Yellow Plates
Thebaine	Platinum Chloride	Dense Rosettes

Confirmatory Tests

There are a number of tests which can detect the presence of drugs even when they are present in a very minute quantity For the quantitative and qualitative analysis of drugs, various chromatographic techniques are used which are excellent methods.

Thin layer chromatography (TLC), gas chromatography (GC) and high performance liquid chromatography (HPLC), etc. are some of the examples which are used for confirmatory tests.

Confirmatory tests requires high selectivity and sensitivity towards drugs, as well as their metabolites, and is frequently carried out by GC/MS. Gas chromatography technique is grounded on the parting of unstable (Volatile) samples by their exceptional affinity for the column.

Target drug compounds in the sample are recognized by their holding time when samples are made to run through the chromatographic columns.
Gas Chromatography combined with mass spectrometry is a robust method because structures of anonymous compounds can be recognized after they have been separated using GC method.
HPLC, FTIR, and UV/Vis are other analytical instruments, found in forensic laboratories as corresponding techniques.