presumptive tests Flashcards
brief
a chemical solution that reacts with a specific chemical or functional group
Reaction results in a visual colour change
If reaction positive, then follow up is required
drugs
Usually colorimetric
If drug present, a colour is observed; if not present another colour is observed
Indicative and only qualitative
Followed by confirmatory analysis in lab – quantitative results
what colour is a positive of amphetamine in the marquis test?
orange - brown
what colour is a positive of aspirin in the marquis test?
pink
what colour is a positive of codeine in the marquis test?
purple
what colour is a positive of diphenhydramine in the marquis test?
yellow
what colour is a positive of fentanyl in the marquis test?
orange
what colour is a positive of heroin in the marquis test?
purple
what colour is a positive of meperidine in the marquis test?
orange
what colour is a positive of methamphetamine in the marquis test?
orange - brown
what colour is a positive of morphine in the marquis test?
purple
what colour is a positive of opium in the marquis test?
purple
what colour is a positive of propoxyphene in the marquis test?
black
what colour is a positive of psilocybin in the marquis test?
yellow
3 advantages of presumptive tests
simple
cheap
sensitive
3 disadvantages of presumptive tests
not specific
false positives
false negatives
2 advantages of confirmatory tests
definite answer
specific
3 disadvantages of confirmatory tests
less sensitive
costly
errors can still occur
give 3 areas in forensic science where presumptive and confirmatory tests are employed?
Body fluids
Drugs of abuse
Explosives
microcrystalline tests - analysis of drugs
Used to identify specific drug substances by studying the size and shape of crystals formed when the drug is mixed with specific reagents
thin layer chromatography - analysis of drugs
Separation technique that uses the solubility and physical properties of the controlled substance to separate compounds
Multiple samples and standards can be spotted on the same TLC plate and the results of the separation compared
how do you work out the Rf value in TLC
distance from origin to centre of spot / distance from origin to solvent front
what are the 5 steps of analysis of drugs scheme
Physical examination Sampling and extraction Presumptive tests Preparation of evidence for analysis Bench and instrumental analysis
what are the two types of material heterogeneities which will influence the sampling of illicit drugs
distribution heterogeneity
constitution heterogeneity
mixing and sampling
Opposite quarters are combined to give half the sample, and the process is repeated until a suitable sample size is obtained.
distribution heterogeneity
Differences in how the pieces (fragments, particles or molecules) are distributed spatially
- How well mixed or segregated the material is due to density, particle size and other factors
Different pieces of material make different contributions to the average concentration
- E.g. THC concentration in cannabis plants will differ between bud, leaves, stalk etc.
constitution heterogeneity
Differences in the constitution of the material
- How alike or different the individual particles or molecules are
For solids – variation between individual fragments or particles
For liquids and gases – individual molecules
how do sampling errors occur
• Arise from differences in composition of particles of the material and from the segregation of different particles
homogenisation of the whole material reduces the sampling error
Normally by mortars and pestles
Very impractical for larger seizures
why do labs take a portion from the bulk material as primary sample?
Taking only one portion (increment) from one place of the bulk material can generate error
taking several increments from different spatial positions can reduce error
The smaller the size of the increments the greater the error arising from particulate structure and ‘microscopic’ heterogeneity of the material
name 4 hallucinogens
LSD
Ectasy
magic mushrooms
cannabis
physical examination LSD
LSD is commonly applied to a substrate
Paper dosage units – blotting paper
Small tablets
Microdots
Gelatin forms
Normal dosage: 30-100 mg of LSD
sampling -LSD
Samples must represent the bulk of the material
- Statistical or non-statistical
May be necessary to perform assays on two separate samples
- Instead of combining and pooling
If prepared separately, wide variations in dosage often occurs
what is a presumptive test for LSD
ehrlich reagent
ehrlich reagent
1g p-dimethylaminobenzaldehyde in 50 mL ethanol and 50mL concentrated hydrochloric acid
what colour shows a positive of LSD with ehrlich reagent
grey/violet
problem with ehrlich reagent - LSD
difficult to conduct in field due to small quantities of drug normally present
TLC analysis LSD
Using chloroform and methanol mixtures as solvent (mobile phase)
Spray with Ehrlich reagent when finished
TLC visualisation LSD
Visualise TLC plate under UV light
- 254nm: dark spots on fluorescent background
- 365nm: fluorescent spots and black background
what is a preemptive test for opiates
marquis test
marquis reagent
5 mL 40% formaldehyde in 100 mL conc. sulphuric acid
what colour occurs when morphine or diamorphine is present in marquis reagent
red/purple
what colour occurs when codeine is present in marquis reagent
blue/purple
what colour occurs with fentanyl is present in marquis reagent
yellow-orange
what happens when heroin is present in marquis reagent
Crystal formations in sodium acetate compared with heroin crystals in mercuric iodide
melting point of morphine
254-256 degrees
melting point of codeine hydrochloride
280 degrees
melting point of heroin
173 degrees
magic mushrooms
Blue Bruising (feature of psilocybin-containing mushrooms)
Microscopy
Scanning electron microscopy
- Marquis reagent
- Ehrlich reagent
Thin Layer Chromatography
DNA
name 5 sedatives
cannabis barbiturates alcohol solvents tranquillisers
physical examination - cannabis
Microscopic analysis to look at characteristic
Short hairs (cystolythic) – upper side of leaf
Trichomes – non-glandular hairs on the underside of the leaves
Other features relate to male and female parts of the plant and flowers
what is a presumptive test for cannabis
duquenois - levine test
what are the 3 solvents in duquenois - levine test - cannabis
Solvent A – 2g vanillin, 2.5mL acetaldehyde in 100mL ethanol
Solvent B – conc HCl
Solvent C – Chloroform
what colour does cannabis go in the duquenois -levine test
purple
TLC - cannabis
cannabinoids are extracted from plant material or resin
Plate of silica gel eluted with toluene or xylene:hexane: dimethaylamine (25:10:1)
cannabinol - TLC
orange colour when treated with Fast Blue (fluorescent dye)
cannabinol - TLC
violet colour when treated with Fast Blue
Δ9-THC - TLC
red colour when treated with Fast Blue
how are barbiturates normally found
normally pills
free acid or salt
physical examination fo alcohol
smell
physical examination of tranquillisers
manufacturers marking
how are barbiturates tested
Test bulk powder (crushed pills) by examining solubility in water and ethyl acetate
Free acids are soluble in organic solvent (ethyl acetate) but not in water
Determine pH in water when pill is dissolved
pH 8 or more indicates that barbiturates are present as sodium or calcium salt
what is the presumptive test for barbiturates
dille-koppanyi test
dille-koppanyi test - barbiturates
1% cobalt acetate in methanol (added to the suspected material)
5% isopropylamine in methanol
what colour do barbiturates go in the dille-koppanyi test
blue
barbiturates - TLC
silica gel plate eluted with isopropyl alcohol and chloroform:acetone mix (4:1)
TLC plate developed using a range of reagents to identify individual components
10% NaOH solution sprayed on plate and heated to 1000C for 5 minutes
When fluorescein is sprayed on – pink spots for bromobarbiturates
tranquillisers - TLC
silica gel plate eluted with range of different solvent systems
E.g. chloroform:methanol (90:10)
give 4 examples of stimulants
Amphetamine
Cocaine
Caffeine
Tobacco (nicotine)
physical examination - amphetamine
Amphetamine is normally found as powders
Salts are usually amphetamine sulphates, phosphate or methamphetamine hydrochloride
These can be identified from their crystal size and colour
- Range from white to dark brown/red
what are the 4 presumptive tests for amphetamines
marquis test
ninhydrin reagent
simons reagent
microcrystalline test to differentiate between optical isomers
marquis test - amphetamine colour
positive immediate orange but turning brown
ninhydrin reagent - amphetamine
used to detect primary and secondary amines
amphetamine is a primary amine
ninhydrin reagent - amphetamine colour
pinkish orange with heating
what does simons reagent react with
amines
what two solutions are involved in simons reagent
Solution A: 1g nitroprusside in 50mL distilled water and 2ml acetaldehyde
Solution B: 2% sodium carbonate in distilled water
simons reagent - amphetamine colour
blue colour for secondary amines
what can give false positives in simons reagent for amphetamines
cutting agents
microcrystalline test to differentiate between optical isomers (enantiomers)
5% HAuCl4 in H3PO4 with 5% NaOH
Use the ‘hanging drop’ technique
Reagent crystals with amine vapour to form yellow rod-like crystals for d- and l- forms
Forms oily drops and plate crystals for d-amphetamine
what is a presumptive test for cocaine
scott test
3 solutions of scott test
- 2% cobalt tiocyanate in 1:1 water:glycerine (Solution A)
- Conc HCl (Solution B)
- Chloroform (Solution C)
scott test -cocaine colour
blue
Blue when adding A, pink when adding B and then blue again when add C.
melting point of cocaine
96-98 degrees
melting point of amphetamine phosphate
150 degrees
melting point for amphetamine sulphate
300 degrees
