Elemental analysis in microanalysis is a method used to determine the percentage of elements (usually Carbon, Hydrogen, Nitrogen, Sulfur, and sometimes Oxygen) in a very small sample of a compound. Here’s a explanation of how it’s done:
Step 1: Sample Preparation
- A very small amount of the compound (usually 1–2 mg) is weighed accurately.
- The sample must be pure and dry to get correct results.
Step 2: Combustion (for CHN analysis)
- The sample is burned in a chamber with excess oxygen.
- This converts:
- Carbon → CO₂
- Hydrogen → H₂O
- Nitrogen → N₂ or NOx
Step 3: Detection of Products
- The gases produced are measured using detectors:
- CO₂ is absorbed by a substance that measures carbon content.
- H₂O is absorbed to measure hydrogen.
- Nitrogen is measured using a special detector.
Step 4: Calculation of Percentages
- The amounts of CO₂, H₂O, and N₂ produced are used to calculate the percentage of each element in the original sample.
- Results are compared with the theoretical values to confirm the molecular formula.
Step 5: Optional Oxygen or Sulfur Analysis
- Oxygen is often calculated by difference: 100% − (C + H + N + S).
- Sulfur can be measured using combustion followed by precipitation as barium sulfate.
Summary
- Elemental analysis is very accurate even for tiny samples.
- It is commonly used in organic chemistry to verify the molecular formula of new compounds.