Flashcards
Chapter 28: Ion chromatography
Cards in this deck (42)
- 1Ion chromatography refers to modern, efficient methods forseparating and determining ions on columns with relatively low ion-exchange capacity
- 2The cations will be separated if the stationary phase has aselective affinity for each of the
various cations - 3The cation A+, which is part of the stationary phase, must not betoo strongly held or exchange will not occur.
- 4The concentration of ____ _____ ______ ______ can be used to control the partition ratios of the analyte ionsA+ in the mobile phase
- 5Because ion formation is favored in aqueous solutions, the mobile phase is aqueous, usuallybuffered to a particular pH.
- 6If the stationary phase contains cationic sites, it is capable of exchanginganions.
- 74 important factors in ion exchange (from power point)• Selectivity of the stationary phase (called a resin in IEC).
• The particular ionic form (counterion) of the resin at the start of the analysis.
• The concentration of the counterion in the mobile phase.
• The pH of the mobile phase. - 8The stationary phase or resin commonly used is astyrene/divinylbenzene copolymer (same as porous polymer LC
- 9Highly crosslinked resins are harder, more brittle, less permeable, less susceptible to swelling, andmore
selective. - 10• Weak exchangers can only be used over a limited pH range‒ ≥ 6 for cation resins
‒ ≤ 8 for anion resins - 11The number of ionic sites on the resin determines thecapacity
- 12Divalent cations are _____ _______ held than monovalent ions.more strongly
- 13Common anion resins have a __________ counterion and cation resins have a __________ ion counterion.chloride
hydrogen - 14___________ _____ works as tridentate(three teeth) chelating species in complexation reactionsIminodiacetic acid
- 15_______ ______ improve the separation of divalent metal ionschelating resins
- 16The chelation exchange mechanisms are ______ than ion exchange.slower
- 17chelating resins show strong ___ dependent behaviorpH
- 18when using chelating resins, its important that the chelating species functional group match the• Efficient separations are possible
only by the choice of the correct
chelating functional group. - 19Where Kex is large, a strong tendency existsa strong tendency exists for the solid phase to retain B+
- 20where Kex is small, a strong tendency existsa strong tendency exists for the liquid phase to retain B+
- 21Thus, for a typical sulfonated cation-exchange resin, values for Kex decrease in the orderTl+>Ag+>Cs+>Rb+>K+>NH4+>Na+>H+>Li+
it relates to size
for divalent: Ba2+> Pb2+> Sr2+>Ca2+>Ni+> Cd2+>Cu2+>Co2+>Zn2+>Mg2+>UO22+ - 22_________-based packings have higher capacity than silica-based packings and can be used over a broad pH range.polymer
- 23______-based ion exchangers give higher efficiencies but suffer from a limited pH range of stability and an incompatibility with suppressor-based detectionSilica
- 24Two types of ion chromatography are currently in use:suppressor-based and single-column
- 25eluent suppressor columnThe suppressor column is packed with a second ion-exchange resin that effectively converts the ions of the eluting solvent to a molecular species of limited ionization without affecting the conductivity due to analyte ions. WATER IS PRODUCED
- 26Single-Column Ion ChromatographyThis approach depends on the small differences in conductivity between sample ions and the prevailing eluent ions. To amplify these differences, low-capacity exchangers are used that permit elution with solutions with low electrolyte concentrations. Furthermore, eluents of low conductivity are chosen.
- 27advantage of single ion exchangenot requiring special equipment for suppression. However, it is a somewhat less sensitive method for determining anions than suppressor column methods.
- 28Capillary Ion ChromatographyCapillary ion chromatography utilizes capillary columns of ~0.4 mm diameter, which in turn provides scaled down volumes of reagents and flow rates of about a factor of 100.
- 29Ion-Exclusion Chromatographya separation technique used to separate electrolytes from nonelectrolytes and to resolve mixtures of weak electrolytes by contact with strong ion exchange resins.J
- 30SIzE-ExCLuSIon CHRoMATogRAPHyaka gel, a powerful technique that is particularly applicable to high-molecular-mass species. Packings for size-exclusion chromatography consist of small (,10 μm) silica or polymer particles containing a network of uniform pores into which solute and solvent molecules can diffuse. The average residence time in the pores depends on the effective size of the analyte molecules.
- 31in size-exculsion chromatography, which elutes first?Larger molecules elute first because they are not retained by the pores of the stationary phase.
- 32in gel chromatography, why are interactions with the stationary and mobile phase avioded?interactions lead to lower column efficiency, separation should only happen due to pore interaction of smaller molecules
- 33in gel chromatography, why is there an upper limit to the retention timebecause no analyte species is retained longer than those that totally permeate the stationary phase.
- 34what detector is used for ion-chromatographyelectrochemical detector
- 35ELECTROCHEMICAL DETECTORUniversal detector in ion chromatography.
Requires the analyte to undergo a
reversible oxidation-reduction reaction.
Amperometry (measure voltage vs. current); Voltammetry (measure current vs. voltage); Coulometry (measure charge vs. time)
• Conductometry – measure voltage vs. time - 36why are suppressor column needed with electrochrmical detectorsSuppresses the ionic strength
of the mobile phase so that the
analyte ions can be detected. - 37disadvantages of suppressor column-Vacancy or void peak is negative going.
‒ Resin becomes exhausted and must be regenerated.
‒ A second column increases zone broadening
-reduces the conductivity of the mobile phase - 38why is MS avoided in ion-chromatographybecause of the high salt content that would build up on the skimmer
- 39Two main ionization sources in ion chromatography-Electrospray ionization (ESI)
‒ Inductively coupled plasma (ICP) - 40LIGAND EXCHANGE CHROMATOGRAPHYUsed to resolve enantiomers of amino acids and their derivatives capable of forming bidentate complexes with transition metal ions, such as copper, zinc, and nickel
- 41ION PAIRING CHROMATOGRAPHY (IPC)A reversed-phase liquid chromatographic technique for separation of organic ions and partly ionized organic analytes. An ion pair reagent is added to the
mobile phase. - 42ADVANTAGES OF ION PAIR CHROMATOGRAPHYAnalytes with very large or very small pKa’s are resistant to separation based on pH adjustment can be separated. Better separation of large ions when compared to ion exchange.
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- GRE instrumental analysis Flashcards on Chapter 28: Ion chromatography, created by Ashlin Deatherage on 01/05/2023.
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