Presumptive test Flashcards
(49 cards)
1
Q
What is a presumptive test
A
- They generally are a chemical solution that reacts with a specific chemical or functional group
- The reaction results in a visual colour change (positive)
- Tests are very sensitive but not specific
2
Q
if the reaction is positive what is required
A
follow up analysis
3
Q
drugs- presumptive test
A
- Usually colourimetric
- If drug is present, a colour is observed; if not present another colour is observed.
- Indicative and only qualitative
- Followed by confirmatory analysis in the laboratory – quantitative results
4
Q
types of presumptive tests
A
- Prospect that the unknown substance may be any one of a thousand or more commonly encountered drugs
- Screening tests to reduce these possibilities to a small and manageable number
- Often accomplished by subjecting the material to a series of colour tests – Spot tests
- Characteristic colours for the more commonly encountered compound e.g. illicit drugs
5
Q
marquis reagent
A
Drug-Colour Amphetamine- organe brown aspirin- pink codeine- purple diphenhydramine- yellow fentanyl- orange heroin- purple meperidine - orange methamphetamine- orange- brown morphine- purple opium- purple propoxyphene- black psilocybin- yellow
6
Q
advantages of presumptive tests
A
- Simple – easy to use
- Cheap
- Sensitive
7
Q
disadvantages of presumptive tests
A
- Not specific
- False positives
- False negatives
8
Q
confirmatory test
A
- Confirmatory tests provide a definite answer to the nature of the test
- They may be less sensitive but of course are specific
- Can be costly
- Errors can still occur
9
Q
presumptive/confirmatory test
A
- Body fluids
- Drugs of abuse
- Explosives
10
Q
analysis of drugs
A
- Microcrystalline tests
- Thin layer chromatography
- IR
11
Q
Microcrystalline test
A
Used to identify specific drug substances by studying the size and shape of crystals formed when the drug is mixed with specific reagents
12
Q
TLC
A
Separation technique that uses the solubility and physical properties of the controlled substance to separate compounds (chromatography)
Multiple samples and standards can be spotted on the same TLC plate and the results of the separation compared
13
Q
TLC equation
A
rf= distance from origin to centre of spot/ distance from origin to solvent front
14
Q
analysis of drug scheme
A
- Physical examination
- Sampling and extraction
- Presumptive tests
- Preparation of evidence for analysis
- Bench and instrumental analysis
15
Q
analysis of drug scheme diagram
A
look on ppt
16
Q
heterogenous samples
A
- All real materials are heterogenous
- Two types of material heterogeneities which will influence the sampling of illicit drugs
- Distribution heterogeneity
- Constitution heterogeneity
17
Q
mixing and sampling
A
seen on previous ppt
18
Q
distributing heterogeneity
A
- 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.
19
Q
constitution heterogeneity
A
- 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
20
Q
how does sampling errors arise
A
from differences in composition of particles of the material and from the segregation of different particles
21
Q
what reduces sampling errors
A
- Homogenisation of the whole material
–Normally by mortars and pestles
Very impractical for larger seizures
22
Q
how does homogenisation work
A
- Laboratories usually 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 this error
o The smaller the size of the increments the greater the error arising from particulate structure and ‘microscopic’ heterogeneity of the material
23
Q
hallucinogens
A
- LSD – lysergic acid diethylamide
- Ecstasy
- Magic mushrooms
- (Cannabis)
24
Q
physical examination of LSD
A
- LSD is commonly applied to a substrate
- Paper dosage units – blotting paper
- Small tablets
- Microdots
- Gelatin forms
- Normal dosage: 30-100 mg of LSD
25
sampling - LSD
- Samples must represent the bulk of the material
Sampling plan? 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
26
Presumptive test-LSD
| Ehrlich reagent
– 1g p-dimethylaminobenzaldehyde in 50 mL ethanol and 50mL concentrated hydrochloric acid
- Positive is denoted by a grey/violet colour
• Difficult to conduct in field due to small quantities of drug normally present
27
TLC analysis- LSD
- Using chloroform and methanol mixtures as solvent (mobile phase)
- Spray with Ehrlich reagent when finished
- Contains p-dimethylaminobenzaldehyde
Visualise TLC plate under UV light
245nm: dark spots on fluorescent background
365nm: fluorescent spots and black background
28
physical examination- opiates
- Heroin
| - Morphine
29
presumptive tests for opiates - marquis test
Heroin, morphine and opiate derivatives
5 mL 40% formaldehyde in 100 mL conc. sulphuric acid
- Positive denoted by a red/purple colour for morphine and diamorphine, blue/purple for codeine and yellow-orange for fentanyl (synthetic opioid)
- For heroin, different crystals forms will exist in different reagents
Crystal formations in sodium acetate compared with heroin crystals in mercuric iodide
30
melting point- opiates
- Morphine: 254-2560C
- Codeine hydrochloride: 2800C
- Heroin: 1730C
31
magic mushrooms
- Blue Bruising (feature of psilocybin-containing mushrooms)
- Microscopy
- Scanning electron microscopy
Marquis reagent
Ehrlich reagent
- Thin Layer Chromatography
- DNA
32
sedatives
- Cannabis
- Barbiturates
- Alcohol
- Solvents
- Tranquilisers
33
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
34
presumptive test- cannabis
| duquenois- levine test
Solvent A – 2g vanillin, 2.5mL acetaldehyde in 100mL ethanol
Solvent B – conc HCl
Solvent C – Chloroform
- Positive denoted by a purple colour
- The purple colour develops in the chloroform
- Found to be not effective in 2000 and today Fast Blue dye is used as it is superior
35
cannabis
| TLC- cannabinoids are extracted from plant material or resin
- Plate of silica gel eluted with toluene or xylene:hexane: dimethaylamine (25:10:1)
- Cannabidiol – orange colour when treated with Fast Blue (fluorescent dye)
- Cannabinol – violet colour when treated with Fast Blue
- Δ9-THC – red colour when treated with Fast Blue
36
physical examination- sedatives
- Barbiturates – normally pills
- Alcohol and other solvents – smell
- Tranquilisers – manufacturer’s marking
37
physical examination- barbiturates
- Barbiturates – free acid or salt
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
- Are there any fillers/contaminants that might help with identification?
38
presumptive test- barbiturates
| dille-koppanyi test
- 1% cobalt acetate in methanol (added to the suspected material)
- 5% isopropylamine in methanol
Positive denoted by a blue colour
39
barbiturates
| TLC – silica gel plate eluted with isopropyl alcohol and chloroform:acetone mix (4:1)
– 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
40
presumptive test- tranquillisers
TLC – silica gel plate eluted with range of different solvent systems
- E.g. chloroform:methanol (90:10)
41
stimulants
- Amphetamine
- Cocaine
- Caffeine
- Tobacco (nicotine)
42
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
43
presumptive test- amphetamine
| marquis teest
- Positive immediate orange but turning brown
44
presumptive test- amphetamine
| ninhydrin reagent
used to detect primary and secondary amines
- Amphetamine is a primary amine
- Positive denoted by pinkish orange (with heating)
45
presumptive test- amphetamine
| Simon's reagent
reacts with amines
- Solution A: 1g nitroprusside in 50mL distilled water and 2ml acetaldehyde
- Solution B: 2% sodium carbonate in distilled water
- Positive denoted by a blue colour for secondary amines
- Can differentiate between methamphetamine and amphetamines
- Cutting agents can give false positive
46
presumptive test- amphetamine microcrystalline test
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
47
enantiomers
superimposable mirror images
48
presumptive test- cocaine
| Scott test
- 2% cobalt tiocyanate in 1:1 water:glycerine (Solution A)
- Conc HCl (Solution B)
- Chloroform (Solution C)
- Positive denoted by a blue colour
- Blue when adding A, pink when adding B and then blue again when add C.
49
melting point for stimulants
- Cocaine: 96-980C
- Amphetamine phosphate: 1500C
- Amphetamine sulphate: 3000C
