Go beyond simple ingredient labels. A technical guide to understanding chemotypes, physical density tests, and batch records.
Technical Quality Sheets (COA)
When buying essential oils in bulk or seeking true therapeutic-grade quality, reputable suppliers will provide a Certificate of Analysis (COA) and a physical specifications sheet. These technical documents confirm that the batch meets established scientific ranges of purity, density, and chemical composition.
Key Specifications Explained
1. Specific Gravity (SG)
This measures the density of the essential oil at 20°C compared to pure water. Since essential oils are lighter than water, their SG is usually between 0.800 and 0.990. If an oil has an SG of 1.0 or higher, it may contain heavy synthetic diluents like phthalates.
2. Refractive Index (RI)
RI measures how much light bends as it passes through the liquid. Every pure oil has a unique refractive index range (usually between 1.450 and 1.510). Adulterating the oil with mineral oil or cheap carrier oils shifts this number, revealing the manipulation.
3. Optical Rotation
This measures how polarized light rotates as it travels through the oil's natural molecules. Synthetic fragrance molecules are often optically inactive, whereas pure botanical molecules will rotate light left (levorotatory) or right (dextrorotatory).
4. Chemotype (ct.) Designation
A plant growing in a dry Mediterranean climate might produce high levels of camphor, while the exact same species growing in a humid valley yields high cineole. The chemotype (ct.) specifies which active organic component dominates the oil.
Batch Tracking & Transparency
Every genuine distillation cycle produces a unique chemical ratio. Professional aromatherapists use batch numbers to match their bottle directly to its lab testing. If a brand sells multiple "batches" over years under the exact same sheet, the tests are outdated or fake.
Technical Sheets Safety & Verification
- Confirm Date Match: Ensure the test date matches the manufacturing or importing timeline of the batch.
- Review Solvents Column: A high-quality sheet should confirm "Zero ppm" of hexane, benzene, or other heavy extraction solvents.
Frequently Asked Questions
What is a chemotype (ct.) in essential oils?
A chemotype (abbreviated as ct.) indicates that plants of the exact same genus and species have produced essential oil with a significantly different chemical composition due to variations in climate, soil, or altitude (e.g., Rosemary ct. cineole vs. Rosemary ct. camphor).
What are Refractive Index and Specific Gravity?
These are physical quality control specifications. Specific Gravity measures the density of the oil compared to water, while Refractive Index measures how light bends as it passes through the oil. Deviations from standard ranges indicate dilution or synthetic alteration.
Why is the batch number important?
Every single distillation cycle yields a slightly different profile of aromatic compounds. The batch number links your specific bottle to its matching lab-certified GC-MS and specifications sheet.