Ion chromatograph

Date：2025/7/7 17:55:06

I. Core Principles

Based on ion exchange chromatography, it realizes separation by utilizing the difference in affinity between ions in the sample and the stationary phase (ion exchange resin), combined with quantitative analysis by a detector. When the mobile phase (eluent) carries the sample through the chromatographic column, anions/cations flow out successively due to their different exchange capacities with the resin. The detector converts the ion concentration into electrical signals, with qualitative analysis based on retention time and quantitative analysis based on peak area/peak height.

II. Key Structures and Functions

Components	Functions and Characteristics
Injection System	- Injection valve (e.g., six-way valve): Manual or automatic injection, with a sample loop volume usually 10-200μL (e.g., 20μL).
Chromatographic Column	- Types: Anion column: Filled with strongly basic resins (e.g., quaternary ammonium groups) for separating Cl?, SO?2?, etc.; Cation column: Filled with strongly acidic resins (e.g., sulfonic acid groups) for separating Na?, Ca2?, etc.;- Guard column: A pre-installed short column that adsorbs impurities to extend the life of the analytical column.
Eluent System	- Anion analysis: Commonly used sodium carbonate/sodium bicarbonate solutions (e.g., 3.5mM Na?CO? + 1.0mM NaHCO?);- Cation analysis: Commonly used methanesulfonic acid or dilute sulfuric acid (e.g., 20mM methanesulfonic acid), which requires degassing treatment (to avoid bubbles affecting the baseline).
Detector	- Conductivity Detector (CD): Most commonly used, based on changes in solution conductivity, with a detection limit as low as μg/L level, suitable for inorganic anions/cations (e.g., F?, NO??);- Ultraviolet Detector (UV): Used for detecting ions with ultraviolet absorption (e.g., NO??, CrO?2?);- Amperometric Detector (AD): Sensitive to reductive/oxidative ions (e.g., CN?, sulfide ions).
Suppressor (Key Component)	- Function: Reduces the background conductivity of the eluent and improves detection sensitivity.- Principle: In anion analysis, the suppressor converts CO?2? in the eluent into HCO?? (a weak electrolyte), and simultaneously converts sample ions into highly conductive acids (e.g., Cl? → HCl).

III. Typical Analysis Process

Sample Pretreatment:

Liquid samples: Filtration (0.22μm filter membrane), dilution (e.g., detection of fluoride ions in drinking water);

Solid samples: Ultrasonic extraction (e.g., chloride ions in soil), centrifugation, and then taking the supernatant for injection.

Instrument Parameter Setting:

Eluent flow rate: 1.0-1.5mL/min (e.g., set to 1.2mL/min for anion analysis);

Column temperature: Usually maintained at room temperature or 30℃ (to improve reproducibility).

Separation and Detection: The sample passes through the chromatographic column with the eluent. After the suppressor reduces the background conductivity, the conductivity detector records the signal in real-time.

Result Analysis: Qualitative analysis based on the retention time of standard samples, and quantitative analysis by external standard method/internal standard method (e.g., preparing a mixed standard solution of F? and Cl? to establish a curve).

IV. Core Application Fields

Industry	Examples of Detection Objects
Environmental Monitoring	Anions in water (F?, Cl?, NO??, SO?2?), water-soluble ions in atmospheric particulate matter (e.g., NH??, SO?2?).
Food and Pharmaceuticals	Preservatives in food (e.g., sodium benzoate), organic acids in beverages (e.g., citric acid, malic acid), inorganic impurities in pharmaceuticals (e.g., sulfate).
Chemical Industry and Metallurgy	Ion concentration in electrolytes (e.g., NaOH, NaCl), trace analysis of non-metallic elements (e.g., sulfur, phosphorus) in steel.
Electronics and Semiconductors	Trace ions in ultrapure water/reagents (e.g., Na?, Cl?) to ensure a clean environment for chip manufacturing.
Life Sciences	Organic acids in biological samples (e.g., lactic acid in blood), amino acids (analyzed after derivatization).

V. Comparison with Other Chromatographic Technologies

Comparison Item	Ion Chromatography (IC)	Gas Chromatography (GC)	High-Performance Liquid Chromatography (HPLC)
Separation Objects	Ionic compounds (inorganic anions/cations, organic acids/bases)	Volatile, thermally stable organic compounds	Polar/non-polar organic compounds, biological macromolecules
Mobile Phase	Aqueous solution (eluent, containing ion-pair reagents)	Gas (carrier gas)	Organic solvent/water mixture
Detector	Conductivity, ultraviolet, amperometric	FID, ECD, TCD	Ultraviolet, fluorescence, evaporative light scattering
Sample Pretreatment	Simple (mainly filtration)	Complex (requires derivatization or extraction)	Moderate (requires dissolution, filtration)

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