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Analytical Chemistry Semester One > ALL > Flashcards

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1
Q

What is Qualitative analysis? And what might this include?

A

What do we have?
Identifying new molecules - confirming new molecules studying reaction mechanisms and quality control
Confirming the identity/ purity of new molecules

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2
Q

What is Quantitative Analysis and what might this include?

A

How much do we have?
Measures the quantity of a substance, compound, ion, atom or molecules grouping, which is presented for analysis
Large range of analyses requires a wide range of methods
Environmental, pharmaceutical, medical, health, legal , forensics, materials

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3
Q

What questions do you have to ask yourself about how you carry out an analysis? E.g. Drug testing in athletes

A

How do you get the sample?
How do you maintain the sample?(identity, stability)
What’s the drug mixed with- how would you separate this?
How would you do the analysis?
Are the results reliable? Uncertainty in measurements, identification etc?

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4
Q

What are the 7 steps that need to be considered when carrying out an analysis?

A
  1. Formulate the problem
  2. Select the analytical method
  3. Obtains samples
  4. Sample prep
  5. Make the measurements
  6. Consider the significance of the result
  7. Draw the conclusions and report
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5
Q

What needs to be considered when formulating the problem?

A

What will be measured and what will the results be shed for? The purpose of the experiment often determines how it is performed
Consider cost, convenience, ease of analysis, time available, equipment, personnel etc.

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6
Q

What needs to be considered when selecting the analytical method?

A

What methods detect the analytical at the required sensitivity

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7
Q

What needs to be considered when obtaining samples?

A

Is the sample representative of the whole?

Usually take several samples to get statistically valid results

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8
Q

What needs to be considered when preparing samples?

A

Is the sample suitable for the analysis?
Does it need to be dissolved/ separate from the matrix or from interferences?
We must not lose the material of interest
Must not introduce impurities into the sample

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9
Q

What needs to be considered when making the measurements?

A

Measure the property of the analyte together with any repeats, blanks or calibrations that are needed.
Need to express the concentration in appropriate units

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10
Q

What needs to be considered when considering the significance of the results?

A

How accurate and precise are the results
What is the uncertainty?
Are there any interferences
How valid is the result

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11
Q

What needs to be considered when drawing conclusions and reporting the result?

A

Have the results answered the question and solved the problem

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12
Q

What are the 7 SI units?

A

Metre, kilogram, second, ampere, kelvin, candela, mole

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13
Q

What steps need to be taken to ensure quality assurance and significance of results are considered?

A

Standard and blank runs
Is the result chemically valid
Does it seem reasonable
Is it statistically valid

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14
Q

Define accuracy

A

How close the result is to the real value

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15
Q

Define precision

A

How close together are reparations measurements

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16
Q

What physical interactions are involved in chromatography?

A 
Solubility
Ionic interactions
Van der waals forces
Dipole-dipole, dipole-induced dipole, dispersion
Hydrogen
Size
Shape
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17
Q

What is the IUPAC definition of chromatography?

A

Chromatography is a physical method of separation in which the components to be separated are distributed between 2 phases.one of which is stationary (stationary phase) while the other (mobile phase) moves in a definite direction

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18
Q

What are the parameters that determine the effectiveness of separation?

A

Operational
Column temp isothermal/gradient
Carrier gas velocity and flow rate
Amount of sample injected

Column parameters
Length
Internal diameter
Film thickness
Stationary phases composition
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19
Q

What 2 things is the quality of separation determined by?

A

The relative retentions - efficient chromatography

Peak widths - efficient columns

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20
Q

Name and outline the steps involved in undertaking an analytical toxicology experiment?

A

Pre-analytical obtain details of suspected poisoning episode. Obtain the patients medial and occupational history. Decide the priorities for the analysis
Analytical - perform the agreed analysis
Post-analytical interpret the results

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21
Q

What questions are involved in analytical toxicology?

A
  1. What sample should be collected/is relevant?
  2. How should it be prepared?
  3. Which analytical technique should be chosen?
  4. Qualitative and quantitative analysis - screening tests or target analysis?
  5. Disposition of xenobiotics in the body - look for parent compound or metabolite
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22
Q

What is phase one metabolism?( functionalisiation)

A

Chemical modification of the original xenobiotic molecule by oxidation, reduction or hydrolysis (this may activate the compound)

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23
Q

What is phase 2 metabolism? (Conjugation)

A

Conjugation reactions in which a second hydrophilic molecule such as glucuronic acid is added to the molecule

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24
Q

What processes are involved in phase 1 metabolism?

A
  1. Oxidation
  2. Reduction
  3. Hydrolysis
  4. Hydration
  5. Dehalogenation
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25
Q

What processes are involved in phase 2 metabolism?

A
  1. Sulphation
  2. Glucuronidation
  3. Glutathione conjugation
  4. Acetylation
  5. Amino acid conjugation
  6. Methylation
26
Q

What is the organic solvent water partition coefficient P

A

Ratio of the concentration of unionised compound X in organic solvent (e.g. In octanol, chloroform) to concentration of compound X in water

27
Q

What is the organic solvent-water distribution coefficient(D)?

A

Ratio of the sum of the concentrations of all forms (ionised and un-ionised) of the compound X in organic solvent (e.g. Octanol, chloroform) in each of the two phases

28
Q

What are the characteristics of a lipophilic xenobiotic substance?

A

Rapidly absorbed
Rapidly and widely distributed in body tissues
Extensively metabolised before it is excreted

29
Q

How is pKa defined?

A

The pH where the chemical exists as 50% ionised and 50% unionised

30
Q

What is the analytical procedure of rapid screening techniques?

A

(E.g. Rapid screening, immunoassay techniques)
For rapid analysis
No sample preparation required
Low sensitivity and selectivity
Usually allow for detection only of any drugs/ poisons in the samples

31
Q

What is the analytical procedure of advanced analytical techniques?

A 
(E.g. HPLC, GC, MS, NMR)
Take time
Require sample preparation
Very sensitive and selective
Allow for identification and quantification of drugs/poisons
32
Q

What steps are involved in the analytical procedure?

A

Sample collection
Sample preservation
Sample preparation
Sample analysis

33
Q

What extraction procedures are there for non-/semi- volatile compounds from liquids?

A

Liquid-liquid extraction (LLE)
Solid-phase extraction (SPE)
Solid-phase microextraction (SPME)

34
Q

What extraction procedures are there for non-/semi- volatile compounds from solids

A 
Soxhlet extraction
Ultrasonic extraction (sonication)
Supercritical fluid extraction
Accelerated solvent extraction
Microwave assisted extraction
35
Q

What extraction procedures are there for volatile compounds from solids and liquids?

A

Static headspace extraction
Dynamic headspace extraction - purge and trap
Solid-phase microextraction

36
Q

Describe the solid phase extraction mechanism

A

Sorption of analyses from solution on solid phase based on affinity of analytes for the solid phase

37
Q

What is the application, sorbent, interactions and eluents for normal-phase SPE?

A

Application: extraction of polar analytes from non-polar samples
Sorbent: activated alumina, silica gels
Interactions: polar interactions (hydrogen bonding, dipole-dipole)
Eluents: polar solvents

38
Q

Give examples of normal-phase SPE sorbent

A

Silica (SiO2)
Alumina (Al2O3)
Bonded silica sorbents

39
Q

What is the applications, sorbents, interactions and eluents of reversed-phase extraction?

A

Application: extraction of non-polar analytes from polar samples (e.g. Water)
Sorbents: hydrophobic particles bonded-phase silica, copolymers
Interactions: nonpolar interactions (van der Waals forces)
Eluents (nonpolar solvents): hexane, ethyl acetate, acetone but also methanol, acetonitrile)

40
Q

Give examples of reversed phase SPE sorbents

A

C8-bonded phase (octyl-) silica

C18 bonded phase (octadecyl-) silica

41
Q

What is chemically modified silica?

A

Silanol groups on the surface of silica are chemically modified to give stationary phases with specific properties

42
Q

What are the applications, sorbent, interactions and eluents of ion-exchange SPE?

A

Application: extraction of ionic analytes from polar solvents
Sorbent (ion-exchange particles): silica gel or polymers containing cation or anion functional groups
Interactions: action and anion exchange
Eluents: (high ionic strength, required pH)
Buffers, salt solutions

43
Q

If pH is greater than pKa by 2 units what distribution will you get for weak acids and bases?

A

100% dissociated product

44
Q

If pH is less than pKa by 2 pH units what is the distribution of weak acids and bases?

A

100% undissociated product

45
Q

Give examples of ion exchange SPE sorbents

A 
Apolar polymeric resins or silica sorbents containing ionised or unionisable functional groups:
Primary amines
Quarternary amine
Carboxylate acid 
Aromatic sulphonic acid
46
Q

What are mixed mode SPE sorbents?

A

Have multiple retentive sites on an individual particle that exploit different retention mechanisms

47
Q

What adsorptive centres are found on the surface of silica?

A 
Free silanols
Geminal silanol
Associated (vicinal) silanols
Silanols near metal cations
Siloxanes
48
Q

What is the pH stability of silica?

A

1-8

49
Q

What is the pH stability of styrene-divinylbenzene?

A

1-13

50
Q

What is the isocratic mobile phase regime?

A

When the mobile phase remains constant over the course of separation

51
Q

What is the gradient mobile phase regime?

A

When alteration of the composition of the mobile phase during the course of the chromatographic run

52
Q

What are volatile buffers needed for

A

Light scattering detection
Coupling with mass spectrometry
Preparative separations

53
Q

Why is the pH of mobile phase so important in both ion exchange chromatography and reversed phase HPLC?

A

The ion exchange mechanism is controlled by pH
pH influences retention time and peak shape in reversed phase HPLC. The pH level affects the degree of dissociation of acidic/basic compounds and free (residual) silanol groups on the surface of stationary phase

54
Q

What are mobile phase additives

A

Small % of additives or modifiers added to a mobile phase to improve peak shapes, retention times and to modify selectivity

55
Q

What are the advantages of increase in temperature in HPLC?

A

The performance of a column often increases because of the decrease of mobile phase viscosity which improves mass transfer
Analysis time decreases due to the possibility of using higher flow rates of the mobile phase due to the increase in diffusion coefficients
It is necessary to work at higher temperatures if the mobile phase is viscous-less pressure is needed to pump the mobile phase

56
Q

What are the disadvantages of increase in temperature in HPLC?

A

Solvent of sample are more likely to decompose
The vapour pressure of the solvent rises thus increasing the risk of bubbles in the detector- uneven baseline, ghost peaks

57
Q

What is the maximum temperature silica and chemically bonded stationary phases should not exceed?

A

120 and 80 degrees respectively

58
Q

What does a variable UV-Vis detector do?

A

Allows for the choice of one wavelength in order to accommodate the absorption characteristics of a particular solute or group of solutes

59
Q

What does a photo diode array detector do?

A

Allows for an access to all of the wavelength s simultaneously
An entire spectrum of light is passed through the detector cell
The light is then bounced off a grating and detected using a multiple array of photodiodes

60
Q

What does a fluorescence detector do?

A

Measures the emission of radiation from a molecule which has attained an excited electronic state after the absorption of radiation

61
Q

What are the applications of a fluorescence/UV detector?

A

Compounds that fluorescence or which fluorescing derivatives can be obtained
Due to small number of molecules which show fluorescence this type of detection can be used for the detection of trace quantities of analyte in complex matrices

Analytical Chemistry Semester One (2 decks)

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