analytical separations Flashcards
chemical analysis
provides chemical information about the constituents in the sample
typical sample consist of
analytes, matrix, and interference or interferent
constituents of interest
analytes
consist of all other constituents in a sample except for the analytes
matrix
component species of the matrix that causes an error in an analysis by enhancing or attenuating the quantity being measured
interference or interferent
a measure of a method’s freedom from interferences
selectivity
techniques or reactions that apply for only a few analytes are
selective
techniques or reactions that work for only one analyte are said to be
specific
one important part of an analysis
dealing with interfering substances by separating analyte from the interfering species
most powerful and widely used methods of treating interferences
separation techniques
useful when there is a significant difference in at least one of the chemical or physical properties between analyte and interferences
separation techniques
what are the separation techniques
- filtration
- centrifugation
- masking
- distillation; sublimation; recrystallization
- precipitation; electrodeposition; volatilization
- extraction; chromatography
most basic physical property we can exploit in a separation
size
uses a porous medium such as a filter paper or membrane through which only the analyte or the interferent can pass
filtration
solution passing through the filter
filtrate
material retained by the filter
retentate or residue
used to separate particles that cannot be separated using filtration process
centrifugation
factors affecting centrifugation separation
particle shape and viscosity
the interference bind to a ligand forming a strong soluble complex that prevents it from interfering in the analyte’s determination
masking
considered a pseudo separation technique bcs it can only chemically isolate the interference from the analyte
masking
use to separate volatile analyte from nonvolatile interferent — separation due to difference in boiling point
distillation
transition of a substance from the solid to the gas state
sublimation
requires large solubility differences between analyte and potential interferences
precipitation
metal can be purified from other metal by first dissolving it on appropriate acid and by application of a specific voltage a specific metal can deposit on an electrode
electrodeposition
separation is based on the extent to which solute distribute themselves between two immiscible liquids
liquid-liquid extraction
the liquid sample is passed through a cartridge that contains a solid absorbent
solid phase extraction (SPE)
can retain low to moderate polarity species from organic matrices such as fat soluble vitamins; steroids
silica solid phase
can retain hydrophobic species from aqueous matrices like caffeine, sedative, polyaromatic, hydrocarbons, carbohydrates, pesticides
octadecyl (C-18) solid phase
common example of solid phase extraction
ion exchange
a reversible chemical reaction wherein an ion from solution is exchanged for a similarly charged ion attached to an immobile solid particle
ion exhange
high molecular weight polymers that contain large numbers of an ionic functional group per molecule
synthetic ion-exchange resins
cation exchange resins and anion exchange resins contain what groups?
cation: acidic groups, anion: basic groups
resin types
- strong acid cation resins
- weak acid cation resins
- strong base anion resins
- weak base anion resins
continuous extraction process
soxhlet extraction
why is continuous extraction conducted
bcs analyte with an unfavorable partition coefficient needs single extraction will not recover all the analyte
most used supercritical fluid, sometimes modified by co-solvents such as ethanol or methanol
carbon dioxide (CO2)
process of separating one component from another
supercritical fluid extraction
substance at a temperature and pressure above the critical point and have both gaseous and liquid properties
supercritical fluid
defined as a point on a phase diagram where both the liquid and gas phases of a substance have the identical density and are therefore indistinguishable
critical point
