Analytical Forensics > Sampling and Sample prep > Flashcards

Sampling and Sample prep Flashcards

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1
Q

What are the general steps in chemical analysis?

A
  1. Formulating the question or defining the problem
  2. Designing the analytical method
  3. Sampling and sample storage
  4. Sample preparation
  5. Analysis
  6. Assessing and analysing the data
  7. Method validation
  8. Documentation
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2
Q

What is qualitative analysis?

A

What is present?

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3
Q

What is quantitative analysis?

A

How much is present?
-Amount of analyte in a sample

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4
Q

What are the 3 components of an analytical sample?

A

-Sample analyte
-Sample matrix
-Interferent

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5
Q

What is the sample analyte?

A

Substance whose chemical constituents are being identified and measured

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6
Q

What is the sample matrix?

A

Components of a sample other than the analyte of interest

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7
Q

What is an interferent?

A

Anything in the sample that can affect the result
-Chemicals that have a similar chemical structure

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8
Q

What are blank samples?

A

Measures the sample solvent response

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9
Q

What is a system suitability sample?

A

A calibration standard is used to confirm that the HPLC system and column are working

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10
Q

What are calibration standards?

A

A series of standards containing an increasing known concentration of your analyte

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11
Q

What does good sample prep ensure?

A

-representative sample
-avoid instrument damage
-ensure conditions of sample are optimum for analysis
-increases concentration of analyte for detection

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12
Q

What are real samples without internal standards?

A

Real samples show the peaks of the analyte if present and all peaks of the sample matrix that couldn’t be removed during sample prep

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13
Q

What are real samples with an internal standard?

A

Real samples would show the peaks of your analyte if present and all peaks of the sample matrix that couldn’t be removed during sample prep

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14
Q

Why do we need good sample prep?

A
  1. Analyse a representative sample
  2. Avoid damage to instruments
  3. Separate sample from other components
  4. Increase concentration of the analyte for detection
  5. Ensure optimal physical conditionsfor analysis
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15
Q

Where can contamination occur during the sampling process?

A

From collection tools and storage containers

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16
Q

What are aliquots?

A

Make room for multiple test portions of sample for replicate analysis

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17
Q

What are subsets?

A

Small quantity of material that reflects the same properties that exist in a larger population for a representative sample

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18
Q

What do subsets prevent?

A

False positives and negatives

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19
Q

What are homogenous samples?

A

-Standard materials
-Pure

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20
Q

What are heterogenous samples?

A

-not uniform
-composition varies from one part of the sample to another

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21
Q

What are environmental samples?

A

-Water
-Soil
-Vegetation
-Wipes
-Swabs
-Food
-Filtrates
-Bulk items
-Fomites

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22
Q

What are clinical samples?

A

-Feces
-Urine
-Blood components
-Sputum
-Fluids
-Washes
-Tissues
-Hair

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23
Q

What factors affect sample storage?

A

-Safety of the sample
-Concentration of analyte in the sample
-Form sample is in
-How long will the sample last
-How much sample we have
-How will it be stored

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24
Q

How can we dissolve solid samples for analysis?

Study These Flashcards
A

-Grind using pestle and mortar
-Mill sample using ball mill
-Sonicator using electrosonic waves

25
What are the extraction techniques for inorganic analytes?
-Ashing -Acid digestion and dissolution
26
What are extraction techniques for organic analytes?
-Solvent extraction -Liquid-liquid extraction -Solid-phase extraction
27
What is ashing used for?
inorganic and heavy metal samples
28
What is ashing?
Removal of organic material from a sample by incineration, converting organics to CO₂ and H₂O, leaving inorganic components as solid oxides.
29
What is dry ashing?
solid decomposes on its own
30
What is wet ashing?
solid decomposed in an acid
31
What is acid dissolution and digestion used for?
inorganic materials
32
What is acid dissolution and digestion?
-Concentrated acid added to sample then heated -Choice of acid depends on sample
33
How can liquids be separated from insoluble solids?
-Filtration -Centrifugation
34
What is continuous solvent extraction used for?
-Extract the soluble analyte from insoluble sample matrix -Remove the soluble matrix from the insoluble analyte
35
What is the continuous solvent extraction procedure?
1. place sample in thimble 2. place thimble in main chamber 3. place solvent in round bottom flask 4. solvent boiled and condensed into main chamber 5. solvent syphons back down to bottom flask after reaches a particular level taking the analyte with it 6. process repeated
36
What are immiscible solvents?
2 solvents which don't form a homogeneous mixture when mixed
37
What miscible solvents?
2 solvents which don't form a homogeneous mixture when mixed
38
How does hydrogen bonding affect polarity?
O-H and N-H donate H bonds O and N can accept H bonds More H bonding sites = high polarity
39
How do dipole-dipole interactions affect polarity?
Carbonyls C=O can form dipoles which contribute to polarity
40
How do charge-dipole interactions affect polarity?
Ions have the biggest contribution to polarity strongest interaction
41
What are non-polar interactions?
-attractions between molecules that don’t have permanent partial charges - their electrons are shared evenly
42
What are the most polar compounds on the liquid-liquid extraction polarity ladder (polar to non-polar)?
-Water -COOH -Amide -Amine -Alcohol -Ketone -Aldehyde
43
What are the least polar compounds on the liquid-liquid extraction polarity ladder (polar to non-polar)?
-Ester -Aliphatic hydrocarbons -Alkenes -Benzene ring -Alkyl halides -Ether -Nitro
44
What is the process of liquid-liquid extraction?
-Add mixture to a separating funnel -Add second immiscible solvent -Shake and allow layers to separate -Compound partitions between layers -Drain and collect each layer
45
How does liquid-liquid partitioning work?
-A solute distributes between two immiscible liquids based on its solubility -The extent of this is given by the Partition coefficient (Kᴅ)
46
What is the Partition Coefficient equation?
KD​=[A]organic/​[A]aqueous
47
What does the partition coefficient explain?
-Ratio of concentrations in each layer -Higher Kᴅ → more solute in organic layer → better extraction -Choose organic solvent where analyte is most soluble - “Like dissolves like”
48
How does adjusting pH affect analyte solubility?
-turns a molecule into a charged (ionic) or uncharged (neutral) form -Charged (ionic) → dissolves in aqueous layer - polar -Neutral (uncharged) → dissolves in organic layer - non polar
49
What is liquid-liquid microextraction?
-Uses very small volumes (µL) of solvent -Suitable for limited sample amounts -Pre-concentrates analyte → improves detection
50
What is single-drop microextraction?
-Uses a µL syringe to form a small solvent drop -Headspace → drop above solution Extracts volatile analytes -Direct immersion → drop in solution Extracts polar compounds
51
What is dispersive liquid-liquid microextraction?
-Extraction solvent forms fine droplets in aqueous phase -High surface area → very fast extraction -High extraction efficiency -Low solvent use
52
What is hollow fibre liquid phase microextraction?
-Uses a hollow fibre membrane containing organic solvent -Analyte passes through pores into the organic phase -Extraction solvent has high boiling point -Longer extraction time (30–60 min)
53
What is solid phase extraction?
-Separation of an analyte from the liquid phase using a solid phase material
54
What is the bind and elute strategy for solid phase extraction?
-Transfer of dissolved analyte in aliquid phase to a solid phase through absorption -Sample matrix can be washed through the filter using a solvent -Sample is then eluted off in a suitable elution solvent
55
What is the removal/trapping strategy for solid phase extraction?
-Transfer of dissolved matrix in a liquid phase to a solid phase through absorption -Analyte is washed through the column -Matrix components are retained on the solid phase
56
What is Normal Phase vs Reverse Phase (Chromatography)?
Normal Phase Stationary phase = polar (silica) Mobile phase = nonpolar Reverse Phase Stationary phase = nonpolar (C18 hydrocarbon chains) Mobile phase = polar (water + methanol)
57
What are molecularly imprinted Polymers (MIPs) in Solid-Phase extraction?
-a material that can selectively bind to an analyte of choice
58
What is dispersion Solid-phase extraction ?
-Solid phase is a sorbent powder or microspheres -High extraction efficiency due to high surface area – Easy to functionalise (Add different chemical groups)
Analytical Forensics
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