Chromatography in Inorganic Analysis
Chromatography is an analytical technique used to separate, identify, and sometimes quantify different components of a mixture. In inorganic analysis, it is especially useful for separating metal ions, inorganic salts, and coordination complexes that are often difficult to distinguish by classical wet chemistry alone.
How Chromatography is Used in Inorganic Analysis
1. Paper Chromatography
- Used for simple separation of cations and anions.
- Example: Transition metal ions (Cu²⁺, Ni²⁺, Co²⁺, Fe³⁺, Mn²⁺) can be separated based on how far they travel on chromatography paper.
- Each ion gives a characteristic colored spot after spraying with specific reagents (e.g., dimethylglyoxime for Ni²⁺).
2. Thin Layer Chromatography (TLC)
- Similar to paper chromatography but uses a coated plate (silica gel, alumina).
- Can separate inorganic complexes and colored salts.
- Example: Separating rare earth elements (lanthanides) after complexation with organic ligands.
3. Ion Exchange Chromatography
- One of the most powerful tools in inorganic analysis.
- Separates ions based on their affinity for charged resins (cation-exchange or anion-exchange resins).
- Applications:
- Separation of lanthanides and actinides (critical in nuclear chemistry).
- Water analysis – removing or detecting Ca²⁺, Mg²⁺, Pb²⁺, SO₄²⁻, NO₃⁻.
- Analysis of transition metal complexes.
4. Gas Chromatography (GC)
- Rarely used for inorganic salts (since they are not volatile).
- But volatile inorganic compounds like metal carbonyls (Ni(CO)₄, Fe(CO)₅) and halides (SiCl₄) can be analyzed.
5. High-Performance Liquid Chromatography (HPLC)
- Useful for separating metal-ligand complexes in solution.
- Often combined with UV-Vis or mass spectrometry to identify trace metal ions.
Real-World Applications
- Environmental Analysis
- Detecting heavy metals in polluted water using ion-exchange chromatography.
- Nuclear Industry
- Separation of radioactive isotopes (e.g., U, Th, Pu, Am) for fuel reprocessing.
- Forensics
- Identifying inorganic poisons like arsenic or chromium.
- Pharmaceuticals
- Checking purity of inorganic salts used in medicines.
- Geology & Mining
- Analysis of trace metals in ores and minerals.
In short: Chromatography in inorganic analysis is mainly used for separating and detecting cations, anions, and metal complexes, with ion-exchange chromatography being the most significant technique.