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Analytical Chemistry > Sample collection, storage and preparation > Flashcards

Sample collection, storage and preparation Flashcards

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1
Q

what are 8 sample collection considerations?

A

ease of collection

matrix interferences

parent drug and/or metabolites

detection/analysis time

stability of the drugs in the sample

putrefaction

potential for automation analysis

reference data

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2
Q

post mortem forensic toxicology

A

Establish the cause and mode of intoxication/death through the analysis of various fluids and tissues during autopsy

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3
Q

sample collection post mortem (9)

A 
blood
urine
vitreous humour
liver
gastric contents
bile
hair
lung fluid
kidney
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4
Q

ante-mortem forensic toxicology - human performance

A

Evaluating the role of a compound in the modification of human behaviour, usually applied to traffic safety and the respective operation of a motor vehicle, as well as doping in sport.

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5
Q

ante-mortem forensic toxicology - xenobiotics testing

A

Establish prior use or abuse of selected compounds through the analysis of body fluids usually urine. Results from these tests are usually applied to the workplace setting.

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6
Q

sample collection ante-mortem

A 
blood
exhaled air
urine
hair
saliva
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7
Q

blood sample collection time?

A

28 hours ish

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8
Q

saliva sample collection time?

A

a few days

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9
Q

urine sample collection time?

A

from a couple hours to days

weeks for marijuana

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10
Q

hair sample collection time

A

from a couple weeks to months/years

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11
Q

sample collection urine

A

non invasive

collected in post mortem investigations since some toxins show in higher levels in urine

Sample is checked for adulteration by checking the pH, creatine, specific gravity and for any unusual colour or smell

Poor correlation between drug concentrations in urine and drug effects

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12
Q

sample collection saliva

A

Non invasive

Easy to collect

Simple matrix – little interference

Indicative of recent drug use

Many different drugs can be determined

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13
Q

sample collection blood

A

The most satisfactory method for obtaining samples is from venous puncture of the femoral vein

Invasive

Post-mortem blood specimen are taken from two sites

  • Heart
  • Peripheral (femoral vein)

High correlation between blood drug concentration and the effects of the drug

Whole blood, plasma and/or serum

Dried blood-spots (DBS)

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14
Q

sample collection hair

A

Preferably collected from the back of the skull where the average hair growth is fairly constant

In cases with a suspicion of a recent poisoning, analyses of plucked hair may be better

Interval for most drugs during which blood, urine and cut hair may all be negative

Drugs only present in extremely low concentrations

Controversy between active and passive drug use

Good timeline for drug usage

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15
Q

what are the 4 routes of entry for drugs in hair

A

During formation of shaft (anagen phase)

Diffusion from blood stream

Diffusion from secretions

External examination

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16
Q

sample collection bile

A

Can be useful where morphine, benzodiazepines and chlorpromazine are suspected toxins

These toxins are concentrated by the liver and excreted into the gall bladder

Direct collection of bile into a bottle is advised because bile is too viscous to be drawn by a needle

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17
Q

sample collection gastric content

A

Typically done in a sudden death in which the deceased has large quantities of a lethal agent in the stomach

Contents should be empties into a wide mouth jar

In the case of suicide, large amounts of pills can be found in the gastric tract

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18
Q

sample collection brain

A

Useful to assess the impact on the overall body burden

Can establish dose of cocaine in body at time of death

Complex matrix that requires extensive sample clean-up and preparation

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19
Q

2 advantages of blood

A

detect parent compound

correlation between amount of drug and blood concentration

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20
Q

4 disadvantages of blood

A

limited volume

low concentrations of basic drugs and some other poisons

complex matriculates - interferences

invasive method

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21
Q

4 advantages of urine

A

often large volume

high concs of many poisons

simpler matrix than blood

non-invasive method

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22
Q

2 disadvantages of urine

A

parent drug might be present in low concentration

no or little correlation between amount

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23
Q

advantage of gastric contents

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A

may contain large amounts of poison (if ingested)

24
Q

2 disadvantages in gastric components

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A

variable sample

no use if inhaled or injected

25
advantage of hair
usually available even if decomposition advanced
26
2 disadvantages of hair
high sensitivity needed only gives exposure data for the weeks/months before death
27
4 advantages of saliva
often large volumes high concentrations of many poisons simpler matrix than blood non-invasive
28
2 disadvantages of saliva
parent drug might be present in low concentration no or little correlation between amount
29
2 advantages of liver
parent drug and metabolites can be found high concentrations in comparison to other tissues
30
disadvantage of liver
extensive sample prep required
31
advantage of bile
useful for morphine, benzodiazepines and chlorpromazine
32
disadvantage of bile
difficult to sample
33
3 advantages of brain
useful for assessing the overall body burden unaffected by trauma to abdomen and chest establish cocaine dose
34
2 disadvantages of brain
extensive sample prep required little inartistic significance
35
sample storage considerations
Stability in simple matrix Preservations in test tube to prevent putrefaction of blood Tissue stored same as blood but no preservatives in container Volatiles need to be stored properly (e.g. sealed, cooled container)
36
what should samples not be stored in
plastic
37
what are the two reasons why samples need to be stored properly before analysis
to prevent analyte degradation to prevent analyte formation
38
sample storage HCN
formed when certain fuels burn asphyxiant gas - prevents chemical respiration - suffocates even though one can breath highly unstable in blood - degrades rapidly - whole blood needs to be frozen
39
why do we undertake sample preparation
detection techniques are often not responsive to the analyte in the form its present in the sample results may also be distorted by interfering compounds
40
what may sample prep involve
``` dissolution extraction reacting with another chemical species filtering dilution ```
41
matrix effects
matrix are the components of a sample other than the target analyses matrix can severely affect the quality of the results
42
dilute and shoot sample prep
no sample prep - just dilution used for simple sample matrixs fast and simple too crude
43
headspace GC sample prep
no sample prerp- just heating used for liquid or solid matrixs - analyte needs to be more volatile than matrix not suitable for thermally instable compounds too crude
44
precipitation
Used for blood sampled and other protein-rich samples Simple method for removing proteins - Better than heating or cooling sample due to higher efficiency Something is added to the sample to make the proteins precipitate - Salts – sulphates or ammonium - Organic solvent Precipitated proteins are centrifuged - Supernatant then collected
45
Liquid-liquid extraction
One of the most widely employed and useful technique Used for simple matrices such as urine or serum and plasma Simple and straightforward technique, also reasonably effective At least 2 phases of liquids - Selective partitioning of analytes versus contaminants between the 2 phases Immiscible solvents are mixed – one containing the analyte The 2 phases are agitated, by vortexing or shaking, to bring about substantial physical mixing After agitation, the phases are allowed to separate The phase containing the analytes is removed either by careful pipetting or by “freeze-pour” - Placing the samples in a freezer to freeze the aqueous layer, after which the organic layer may be poured off Example: hexane and acetonitrile for barbiturates in serum - Polar drugs end up in the acetonitrile - Lipids from serum will partition in the hexane Could add buffers or pH modifiers (acids, bases) Low extraction efficiency
46
solid phase extraction
Perhaps the most powerful sample prep technique - High selectivity - Flexibility - High automation potential Chromatographic sorbent in a column format Available in variety of format to accommodate different sample sizes and applications
47
SPE column
the extraction device used to execute the SPE protocol. Also called cartridge or extraction plate
48
sorbent
packing used to implement the SPE procedure. also called stationary phase
49
matrix
Liquid present in the SPE sorbent bed at any time. May be either a protocol solvent or the sample itself
50
retention
Occurs when the analytes are attracted to and held by the active chemistry within the sorbent bed
51
elution
Disruption of the attractive interaction between the analytes and the sorbent bed, resulting in the analytes being released from the sorbent and out of the column
52
breakthrough
Analyte passing through the SPE column unretained during sample application, especially when the desired result is retention
53
capacity
mass of retained compounds that may be held by given mass of sorbent
54
SPE
a sample is passed through the column bed and analytes are retained SPE cartridge is washed to remove interferences, and the purified analytes subsequently eluted from the column - Sample matrix liquid passes through May also be used to retain interferences, allowing analytes to pass unretained through the sorbent bed
55
SPE 4 steps
conditioning sample addition washing elution
56
SPE advantages
high output only small amount of sample needed several different sorbents avaliable - high specificity commercial kits available can be automated
57
solid phase micro-extraction
Fibre coated in adsorbent - Polymer (liquid) - Sorbent (solid) Can be used on liquid or gas phase sample Fibre is then inserted into the injection port of the GC - Heating causes analytes to desorb and enter GC column Fast and simple In most cases, no solvent needed

Analytical Chemistry (17 decks)

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