Ion Chromatography is a relatively new technique which employs a novel manner some well-established principles of ion exchange of allows electrical conductance to be used for detection and quantitative determination of ions in solution after their separation.
Since electrical conductance is a property common to all ionic species in the solution, a conductivity detector clearly has the potential of being a universal monitor for all ionic species.
In Ionic-exchange chromatography there is a problem of electrical back ground i.e., the high conductance of HCl in the effluent effectively "swamps" the lower conductance due to Na+ & K+in their separation and determination. So it prevents their measurement by electrical conductance.
In Ion-Chromatography this problem of electrical background is overcome by means of effluent suppression. This in the above example of Na+ - K+ analysis, if the effluent from separating column is passed through a strong base anion exchange resin in hydroxide form (suppressor column) following process occur.
a) HCl + OH-(resin) gives Cl-(resin) + H2O
b) NaCl/KCl + OH- (resin) gives NaOH/KOH +Cl- (resin)
Thus, the sample cations are presented to the conductivity detector not in highly conducting background, but in a very conducting background of de-ionized water.
Ion-Chromatography permits determination of both inorganic and organic species (ionic) often in concentrations of 50ppb or less. Since analysis time is short (less than 20 min) sample volume may be less than 1ml. Ion-chromatography is a fast and economical technique found its applications in different areas of chemical analysis particularly for quantitative determination of anions.
Ion - Chromatography flow scheme:
Separator Column: In this the specific capacity of the column is kept small using resins of low capacity. These resins are stable over a wide pH range.
Suppressor column: Where the electrical conductance is used for sample ion detection in effluent from the column, as eluant background of low conductivity is required. Function of suppressor column is to convert eluant ions into species giving low or zero conductance, e.x., NaHCO3 used as eluant for anion analysis. This is converted into a dilute carbonic acid background using strong strong acid suppressor resin.
Detector used in Ion-Chromatography:
1) Detectors employing electrochemical principles:
i) Conductometric detectors: Optimum mode of detection for strong acid anions (pKa <> 7 ). This has interchangeable Ag & Platinum working electrodes and may be used alone or simultaneously with conductivity detector.
2) Detectors based on optical absorption and emission techniques.
a) Spectrophotometric detectors
Based on the absorbance of monochromatic light by the column effluent according to Beer-Lamberts law. As most organic species have significant absorption in the UV region of the spectrum these detectors have wide applications.
b) Fluorescence detectors:
The ionic species are converted into fluorescent compounds by post column derivatisation and then detected.
Ion-Chromatography has been successfully applied to quantitative analysis of ions in industrial and environmental samples. The technique is valuable for micro-elemental analysis.
Since electrical conductance is a property common to all ionic species in the solution, a conductivity detector clearly has the potential of being a universal monitor for all ionic species.
In Ionic-exchange chromatography there is a problem of electrical back ground i.e., the high conductance of HCl in the effluent effectively "swamps" the lower conductance due to Na+ & K+in their separation and determination. So it prevents their measurement by electrical conductance.
In Ion-Chromatography this problem of electrical background is overcome by means of effluent suppression. This in the above example of Na+ - K+ analysis, if the effluent from separating column is passed through a strong base anion exchange resin in hydroxide form (suppressor column) following process occur.
a) HCl + OH-(resin) gives Cl-(resin) + H2O
b) NaCl/KCl + OH- (resin) gives NaOH/KOH +Cl- (resin)
Thus, the sample cations are presented to the conductivity detector not in highly conducting background, but in a very conducting background of de-ionized water.
Ion-Chromatography permits determination of both inorganic and organic species (ionic) often in concentrations of 50ppb or less. Since analysis time is short (less than 20 min) sample volume may be less than 1ml. Ion-chromatography is a fast and economical technique found its applications in different areas of chemical analysis particularly for quantitative determination of anions.
Ion - Chromatography flow scheme:
Separator Column: In this the specific capacity of the column is kept small using resins of low capacity. These resins are stable over a wide pH range.
Suppressor column: Where the electrical conductance is used for sample ion detection in effluent from the column, as eluant background of low conductivity is required. Function of suppressor column is to convert eluant ions into species giving low or zero conductance, e.x., NaHCO3 used as eluant for anion analysis. This is converted into a dilute carbonic acid background using strong strong acid suppressor resin.
Detector used in Ion-Chromatography:
1) Detectors employing electrochemical principles:
i) Conductometric detectors: Optimum mode of detection for strong acid anions (pKa <> 7 ). This has interchangeable Ag & Platinum working electrodes and may be used alone or simultaneously with conductivity detector.
2) Detectors based on optical absorption and emission techniques.
a) Spectrophotometric detectors
Based on the absorbance of monochromatic light by the column effluent according to Beer-Lamberts law. As most organic species have significant absorption in the UV region of the spectrum these detectors have wide applications.
b) Fluorescence detectors:
The ionic species are converted into fluorescent compounds by post column derivatisation and then detected.
Ion-Chromatography has been successfully applied to quantitative analysis of ions in industrial and environmental samples. The technique is valuable for micro-elemental analysis.
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