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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

A

may contain large amounts of poison (if ingested)

24
Q

2 disadvantages in gastric components

A

variable sample

no use if inhaled or injected

25
Q

advantage of hair

A

usually available even if decomposition advanced

26
Q

2 disadvantages of hair

A

high sensitivity needed

only gives exposure data for the weeks/months before death

27
Q

4 advantages of saliva

A

often large volumes

high concentrations of many poisons

simpler matrix than blood

non-invasive

28
Q

2 disadvantages of saliva

A

parent drug might be present in low concentration

no or little correlation between amount

29
Q

2 advantages of liver

A

parent drug and metabolites can be found

high concentrations in comparison to other tissues

30
Q

disadvantage of liver

A

extensive sample prep required

31
Q

advantage of bile

A

useful for morphine, benzodiazepines and chlorpromazine

32
Q

disadvantage of bile

A

difficult to sample

33
Q

3 advantages of brain

A

useful for assessing the overall body burden

unaffected by trauma to abdomen and chest

establish cocaine dose

34
Q

2 disadvantages of brain

A

extensive sample prep required

little inartistic significance

35
Q

sample storage considerations

A

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
Q

what should samples not be stored in

A

plastic

37
Q

what are the two reasons why samples need to be stored properly before analysis

A

to prevent analyte degradation

to prevent analyte formation

38
Q

sample storage HCN

A

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
Q

why do we undertake sample preparation

A

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
Q

what may sample prep involve

A 
dissolution
extraction
reacting with another chemical species
filtering 
dilution
41
Q

matrix effects

A

matrix are the components of a sample other than the target analyses

matrix can severely affect the quality of the results

42
Q

dilute and shoot

sample prep

A

no sample prep - just dilution

used for simple sample matrixs

fast and simple

too crude

43
Q

headspace GC

sample prep

A

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
Q

precipitation

A

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
Q

Liquid-liquid extraction

A

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
Q

solid phase extraction

A

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
Q

SPE column

A

the extraction device used to execute the SPE protocol. Also called cartridge or extraction plate

48
Q

sorbent

A

packing used to implement the SPE procedure. also called stationary phase

49
Q

matrix

A

Liquid present in the SPE sorbent bed at any time. May be either a protocol solvent or the sample itself

50
Q

retention

A

Occurs when the analytes are attracted to and held by the active chemistry within the sorbent bed

51
Q

elution

A

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
Q

breakthrough

A

Analyte passing through the SPE column unretained during sample application, especially when the desired result is retention

53
Q

capacity

A

mass of retained compounds that may be held by given mass of sorbent

54
Q

SPE

A

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
Q

SPE 4 steps

A

conditioning

sample addition

washing

elution

56
Q

SPE advantages

A

high output

only small amount of sample needed

several different sorbents avaliable - high specificity

commercial kits available

can be automated

57
Q

solid phase micro-extraction

A

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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