Unit 1 Flashcards
what are examples of naturally occurring substances?
water
CHO
peptides
pigments
what are examples of synthetic substances?
functional additives
food colorings
flavorings
what are examples of undesirable chemical substances?
environmental contaminants
process induced contaminants
agrochemical residues
food contact material residues
define analyte
component of a system to be analysed
define matrix
components of the sample other than the analyte
define matrix effect
combined effect of all components of the sample other than the analyte on the measurement of the quantity
define interference
when a specific component is identified to be causing a matrix effect
describe a small molecule
- low molecular wt (below 900Da)
- simple sugars,
AAs, FAs
describe a large molecule
- up to several hundreds of thousands of Da
- proteins, complex CHOs
describe polar compounds
give examples
- soluble in water and protic organic solvents
ex:
- simple sugars
- oligosaccharides
- AAs
- small proteins
describe non-polar compounds
give examples
soluble in non-polar organic solvents (hydrophobic)
ex:
- fats
- phospholipids
- sterol
- liposoluble vitamins
- carotenoids
when the chemical is hydrophobic, Kow will be… (high/low)
high
when the chemical is hydrophillic, Kow will be… (high/low)
low
what is Kow? what is the equation?
octanol-water partition coefficient
Kow = conc (octanol) / conc (H2O)
measure of the difference in solubility between two compounds, which tells you how hydrophobic or hydrophillic the compound is
define solubility of a solute
- analytical composition of a saturated solution
- expressed in terms of the proportion of a designated solute in a designated solvent
what can solubility be expressed as?
concentration molality mole fraction mole ratio etc...
define a non-volatile compound
give examples
- low vapor pressure or high boiling point
- ex: sucrose, NaCl
define a volatile compound
give examples
- high vapor pressure or low boiling point
- ex: essential oils, low molecular wt FAs, flavor compounds
what are some challenges of food analysis?
- complex matrices
- matrix composition may vary among samples (origin and different processes)
- analyses usually need to be performed within a few hours to a few days to maintain sample integrity and respond quickly to the requester
why do analyses usually need to be performed within a few hours/days?
- to maintain sample integrity (microbiological, physical, chemical degradation)
- respond quickly to requester (client’s request, inspection, regulatory compliance)
what are some technologies that allow for direct analysis of food components without sample prep/separation?
- X-ray fluorescence
- infrared spectroscopy and near infrared
- guided microwave spectrometry
- magnetic resonance imaging
is it possible to analyze food without manipulation? how?
yes. Some technologies allow direct analysis of specific food components without sample prep
what is the Bruker handheld XRF food scanner?
- type of portable analyzer that doesn’t require sample prep
some tasks includes:
- salt analysis for iodine
- milk analysis
- nutrient verification
- etc…
what are advantages of direct analysis?
- no sample prep = overall shorter analysis time
- avoidance of cross-contamination
- large potential for automation
- less hazardous chemicals
- less chemical wastes
- no specific chemical facilities
overall: direct analysis = less manpower, consumables or facilities
what are current limitations of direct analysis?
- sensitivity and selectivity
- surface vs bulk
- methods not standardized or approved yet by regulatory agencies
- high instrument costs
what does most sample preparation steps involve?
separation to isolate the target analyte(s) into a fraction that is more appropriate for analysis
define separations
process of any scale by which the components of a mixture are separated from each other without substantial chemical modification
what did Carl Willhelm Scheele do?
first separated citric acid by crystallizing it from lemon juice
define partition/distribution
- terms are used synonymously
- describes general process by which the distribution of a solute between phases comes into equilibrium
define adsorption
the distribution processes that occur between a solute and a phase at the surface of phase
define absorption
the distribution processes that occur between a solute and a phase within the bulk of the phase
define equilibrium
thermodynamic state of a system where the parameters that define its properties (eg. activity or concentration of a solute) remain unchanged
separation methods may be classified based on what?
the driving force for the separation
compare/contrast the driving forces in equilibrium and non-equilibrium
equilibrium: driving force is what attains the equilibrium
non-equilbrium (kinetic): driving force is the rate at which solutes migrate
describe differential centrifugation
which particles will sediment faster/slower?
- particles of different densities or size will sediment at different rates
- largest and more dense particles sediment the fastest
- less dense and smaller particles sediment slower
what driving forces occur in differential centrifugation?
kinetic non-equilibrium forces
it is the driving force which allows solutes to migrate
what are equilibrium driven separation methods?
- partition chromatography extraction
- distillation
- precipitation
- crystallization
what are kinetic driven separation methods?
- dialysis
- electrophoresis
- exclusion chromatography
- centrifugation
- filtration
- sedimentation
- membrane methods
what are hybrid or hyphenated techniques?
what are examples?
- combination of various instrumental methods
ex:
- gas chromatography mass spectrometry
- high performance liquid chromatographu with diode array
