Presumptive testing Flashcards
(25 cards)
What is a presumptive test + ex; higher false neg or pos?
substance is likely present or not present but no ID
- colorimetric
- microcrystal
Low false negative, high false positive
What is a confirmatory test and how is it different from presumptive
confirm ID (usually instrumental analysis)
- chemical principal diff from presumptive
What is a colorimetric test
rxn of sample + reagent or series of reagents = COLOR CHANGE
What is a microcrystalline test
drop of reagent onto small quant sample = UNIQUE CRYSTAL shape and size for ea analyte
- greater specificity
- using PLM
- common in explosives evi
What can you not use a presumptive test for?
Drug purity
What is a Kastle Meyer test?
tests PEROXIDASE ACTIVITY not blood
- from heme group in hemoglobin
- can have cross-reactivity from other oxidizing substances (veggy extract, heavy metals, saliva)
- false negatives when reagents are old or applied incorrectly
How can you reduce false pos & neg in presumptive tests and what is important to keep in mind
- proper controls
- LoD limit of detection
What is Mayer’s reagent test
- indicates narcotic alkaloid (morphine, heroin) or amphetamine
- pos result = white precipitate
What is Marquis’ reagent
- distinguishes btwn alkaloids and amphetamines
- color signature = color and sequence of color change
- VIOLET = opiates (heroin, codeine, morphine)
- PURPLE/ BROWN = amphetamines
What is Mecke’s test
- heroin
mix of selenous acid and concentrated sulfuric acid
Scott’s test for cocaine or Cobalt thiocyanate reagent
- Cocaine rxn w cobalt thiocyanate = blue precipitate ( a lot of false +)
Acidification of solution w HCl to solubize many adulterents but not coca
- PINK
- Pink/ Blue: extraction of cocaine precipitate by adding cholorform = 2 phase solution
- blue organic phase = pos
- colorless orgo phase = neg
What are 3 colorimetric tests for cannabis
- Duquenois- Levine Reagent
- KN reagent
- Fast Blue BB
What doesDuquenois Levine reagent do
Reagents= vanilllin + acetaldehyde
- Cannabis VIOLET
What does KN test for and what color?
- THC
- dark red
What does fast blue test for
TLC? in weed?
What causes incomplete combustion of gunpowder?
The nitrites, usually saltpeter (sodium nitrate)
What tests for nitite ions in solution?
Modified Greiss test (MGT)
How does MGT work?
- nitrite residue + acetic acid solution & heat = nitrous acid
- nitrous acid + sulfanilic acid = diazonium compound
- diazonium compound + alpha naphthol = orange azo dye
What is the positve control for MGT
Paper spiked w dilute sodium sitrate solution
What are the steps of MGT
- evidence on treated paper (sulfanilic acid and a-naphthol)
- ironed with dilute acetic acid steam
- orange if pos
What tests for lead? Where does the lead originate from?
- Sodium Rhodizionate test
- The primer
What is the rxn in sodium rhodizionate test
lead + saturated sodium rhodizionate solution + 2.8 pH buffer solution = pink + 5% HCl = blue vio color
color change from HCl = lead
What indicates a false pos when analyzing GSR?
Reaction ALLL over a garment
What should you do if you suspect a false positive?
- check chemicals to ensure proper reactivity
- clearly document sus of false pos
