Combining IR and GC Evidence

1. Define the claim

Ask whether the product formed, which functional groups are present, whether a mixture is likely, and whether a quantitative yield claim is supported. These are different questions requiring different evidence.

2. Identify independent observations

Recovered mass indicates how much material was collected but not whether it is pure. IR supports functional-group assignments. GC provides method-dependent separation and detector response; peak identification and quantitative composition need standards and calibration.

3. Worked evidence conflict

Imagine a recovered liquid mass that appears too high, an IR spectrum retaining a broad O–H feature, and a GC trace with several peaks. Solvent carryover or unreacted starting material is plausible. The evidence does NOT justify reporting a pure product with >100% yield.

4. Plan the next test

Repeat drying/weighing, inspect raw IR background, run suitable GC standards, and compare replicate chromatograms. Choose the follow-up that most directly discriminates between the proposed explanations.

5. Write a claim-evidence-reasoning conclusion

State the claim, cite at least two measurements with units, explain what each supports, list a plausible alternative, and specify what additional evidence would change your conclusion.

Common interpretation mistakes

• Assuming higher recovered mass means more pure product.
• Treating matching GC retention as proof of molecular identity.
• Discarding contradictory results instead of investigating them.