Pre lec 3- Drug analysis

Question 1

Naturally flourescent compounds

Answer 1

• Are candidates for spectrofluorimetic analysis
  
  • Ergometrine
  • Riboflavine
  • Catecholamines
  • Phenothiazines
  • Chlortetracycline
  • Oxytetracycline
  • Barbiturates (at pH >13)

Question 2

Fluorescent Barbiturates

Answer 2

Question 3

Derivatisation

Answer 3

• Some weakly-fluorescent or non-fluorescent drugs may be derivatised with a fluorescent reagent
• Dansyl Chloride
  
  • Derivatives primary and secondary amines and phenols
• Fluorescamine
  
  • Derivatises primary aliphatic amines including peptides and proteins
• Isatoic Anhydride
  
  • Derivatises primary and secondary amines and alcohols
• o-Phthaldehyde
  
  • Derivatises primary amines

Question 4

Fluorescence spectrophotometry considers

Answer 4

• Fluorescent contaminants
• Extent of derivatisation
• Reliability of the derivatisation reaction

Question 5

Infra-red spectrophotometry

Answer 5

• IR total range = 4000-400 cm^-1
• Fingerprint region= 1600-400 cm^-1
  
  • Complex
  • Unconfirmed origin
  • Characteristic of the particular molecule

Question 6

Infra-red Instrumentation

Dispersive spectrophotomters (old types)

Answer 6

• Scanned absorbance
• Single beam
• Double beam (uses a reference beam to compensate for solvent absorbance
• Usually a real-time chart paper readout
• computational subtraction- sometimes
• Low sensitivity at high absorption

Question 7

Infra-red instrumentation

Dispersive spectrophotometers problems- frequency errors

Answer 7

• Inherent in the instrument
• Adjustment errors
• Chart paper in wrong place
• The pen
• Error greater at higher wavenumbers
• IT IS ESSENTIAL TO CALIBRATE EACH SPECTRUM BEFORE IT IS REMOVED FROM THE READER
• Record the sample spec
• Record a few of the main bands (known) of the spectrum of a sample of polystyrene over the top

Question 8

Fourier transform infra-red (FTIR)- modern

Answer 8

• An interferometric method
• Light from the whole range (5000-400 cm^-1) is split into two beams
• One beam travels a longer path than the other
• One beam passes through the sample
• Beams recombined
• Interference pattern (interferogram) - the sum of all the interference patterns from every wavelength
• Converted via a Fourier transformation to the absorbance spectrum

Question 9

Fourier transform infra-red (FTIR)

Advantages

Answer 9

• Fast- Whole spectrum measure at once- can use for real-time chromatographic output
• Reproducible-
• Accurate (0.01 cm-1 at 4000cm-1 cf 50cm-1 on older, dispersive instruments)
• High resolution- without sacrifice of sensitivity
• Low sample concentrations- add successive scans
• Low stray light levels- ABsorbance linear beyond 3 absorbance units
• Data digital
  
  • Manipulation- subtraction of pure compound possible to reveal other components
  • Spectrum identification- best-fit possibilities with a digital library of authentic compounds
  • Interpretation- computerised function group recognition