1、 Working principle
Ion ChromatographBased on ion exchange technology, ion separation and detection are achieved through reversible exchange of ions between the fixed phase (low exchange capacity ion exchange resin) and the mobile phase (aqueous solution). The core principles include:
Ion exchange separation
Separable ions on the stationary phase resin exchange with solute ions of the same charge in the mobile phase, and different ions have different retention times in the chromatographic column due to differences in affinity, thus achieving separation.
For example, during anion separation, anions such as F ⁻, Cl ⁻, and SO ₄² ⁻ exchange with OH ⁻ on the resin. Ions with weak affinity are eluted first, while those with strong affinity are eluted later.
conductive detection
The separated ions enter the conductivity detector with the mobile phase, and the ion concentration is determined by measuring the change in conductivity.
Suppressor technology: A suppressor is added in front of the detector to convert high conductivity eluent (such as NaOH) into low conductivity components (such as H ₂ O), while converting sample ions into corresponding acids/bases (such as Cl ⁻ → HCl), significantly improving detection sensitivity.
Separation type
Ion exchange chromatography: commonly used and suitable for separating hydrophilic anions and cations.
Ion exclusion chromatography: separates organic acids and oxygen-containing acid ions (such as borate and carbonate ions).
Ion pair chromatography: Separation of hydrophobic anions and metal complexes.
2、 Usage method
1. Preparation before operation
Equipment inspection
Check the rinsing solution system: Open the argon gas cylinder and adjust the pressure reducing valve to 0.2-0.3MPa; Open the rinsing solution air source device and adjust it to 3-6 Psi.
Ensure that the filter head of the mobile phase bottle is always submerged below the liquid level to prevent it from drying up.
Sample processing
Filtration: Use 0.45 μ m or 0.22 μ m microporous filter membranes to remove suspended solids.
Digestion: Liquid samples can be microwave digested with 22% hydrogen peroxide for 1.5 hours to adjust the pH to neutral; Solid samples can be ashed at high temperatures and then soaked in a washing solution.
Removing interfering ions: The high Cl ⁻ sample is treated with an Ag column to remove Cl ⁻; The high SO ₄² ⁻ sample is treated with a Ba column to remove SO ₄² ⁻.
2. Operation process
power on
Power on the host, computer, and printer in order.
Enter the operating interface and initialize the system.
Turn on the pump. If the instrument has not been used for a long time or if the rinsing solution has been replaced, first open the PRIME valve on the balance pump head to exhaust. After the pump pressure stabilizes, turn on the suppressor power supply.
Sample injection and analysis
The sample is introduced through an injector, and the mobile phase carries the sample into the chromatographic column for separation.
When using an anion chromatography column, adjust the current to 70 ± 5mA when passing the mobile phase; after the experiment is completed, turn off the current first and then turn off the pump.
The detector signal is transmitted to the data processing system, generating a chromatogram and calculating ion concentration.
Shut down
Turn off the suppressor current (during cation and anion detection).
Turn off the power supply of the pump and the main engine.
When not in use for a long time, deionized water should be supplied once a week to prevent microbial growth.
3. Ion ChromatographMaintenance and Care
Pump maintenance
Clean the flow path with water for 20 minutes before and after each use.
When not in use for a long time, regularly replace the liquid that may breed microorganisms with deionized water.
Column maintenance
After the experiment, seal and store the chromatography column with a washing solution.
Avoid direct injection of high concentration samples to prevent a decrease in column efficiency.
Suppressor maintenance
When not in use for a long time, inject 0.2mol/L sulfuric acid solution in reverse to activate the biofilm and let it sit for more than half an hour.
When there is leakage or high background conductivity, check if the regeneration liquid flow path is blocked or if the current setting is too low.