1. For one sample, in theory, there are probabaly several analytical methods by various instruments. So you'd better compare their performance-price ratio, operational characteristics, maintenance service. List the reasons why you choose this supplier's GC.

2. Find and consult reference documents regarding analyzed samples, including international standard, national standard, industry standard etc.

3. Consult with others who analyzed and are analyzing the the sample. Usually they will give you useful and valuable advice.

4. Collect as much GC information as you can. Prepare making a final decision.

5. Is your GC job a long term or short term? Different job decides different investment.

6. How about your current conditions? Do you already have a GC? Can it be upgraded? or Just want to buy a new GC directly.