When purchasing Normal Paraffin (C10-C13 or C14-C17), you must prioritize purity levels (typically >98%) and carbon distribution. Key metrics include the Bromine Index, which indicates the level of unsaturated hydrocarbons (should be <20 mg/100g for high quality), and Sulfur content, which must be below 1 ppm for environmental and catalyst protection. Additionally, verify the distillation range and flash point (typically >70°C) to ensure the product meets your specific industrial application requirements.