Analyzing Essential Oils for Composition and Purity

Checking the quality is important as essential oils are widely used in perfumes, cosmetics, soaps and other home care products, for flavoring food and beverages, and for adding scents to household cleaning products.

Some essential oils are used in pharmaceutical products (i.e. Eucalyptus oil) and for aromatherapy.

An essential oil is a concentrated hydrophobic liquid containing volatile chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetherolea, or simply as the oil of the plant from which they were extracted. An essential oil is “essential” in the sense that it contains the “essence of” the plant’s fragrance—the characteristic fragrance of the plant from which it is derived. An essential oil is distilled from leaves, stems, flowers, barks, roots or other parts from plants. Essential oils, contrary to the use of the word „oil“ are not having an oily appearance. Most essential oils are clear, some are yellow or amber in color.

As essential oils are complex mixtures of various chemical constitutes the composition can be affected in every step of the production, beginning with growing and harvesting condition and ending in the storage. Diluting, cutting or extending high purity oils with lower quality and still selling them as „pure“ is one more critical factor.

The international standard ISO to check the quality of essential oils is to measure physical parameters – one of them being the optical rotation – measured in a polarimeter.

The term „Specific rotation“ implies that for a specific substance or mixture at given, reproducible conditions (temperature, concentration, light path length and wavelength) the optical rotation is specific for this substance.

SubstanceSpecific rotation (at 589nm and 20°C)
Mint oil-17° to -24°
Orange oil+94° to +99°

Using our new VariPol polarimeter with complete CFR part 11 compliance and a high reproducibility the quality of an essential oil can be guaranteed. By adding the VariRef refractometer a second parameter – the refractive index – can be determined in parallel.

Normative reference:

  1. ISO 592:1998(en) Essential oils — Determination of optical rotation
  2. ISO 280:1998(en) Essential oils — Determination of refractive index


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