Methods for Analyzing Essential Oil Composition and Purity

Analyzing Essential Oil Purity and Composition Methods

Customers are often in dilemma about quality and purity of essential oils, when buying them. It’s never easy as essential oils are complex blends of various chemical constituents.

What Factors Affect the Quality & Purity of Essential Oil?

The quality of essential oils can be affected by a number of external factors. Some of these factors include growing and harvesting conditions, distillation method, handling, and storage conditions.

In addition, there are some middle men who adulterate these oils in order to make more profit margin.

How to Analyze the Quality/Purity and Composition of Essential Oils?

There are certain ways that can be helpful in analyzing essential oil composition and purity, however not always these testing techniques are 100% accurate to ensure the composition and purity of an essential oil.

In general, there are 3 ways that are used for testing essential oil

  1. Polarimetry (Optical Rotation)
  2. Refractometery (Refractive Index)
  3. Density

Method 1: Measuring Specific Rotation Using Polarimetry

The specific rotation of a substance is referred as the optical rotation of a solution comprising 1 g/ml in a 100 mm polarimeter tube. The solution is affected by temperature (for example 20°C) and Sodium D line wavelength (around 589 nm). After that it can be measured by using below given formula:


α = measured optical rotation

d = light path in dm

c = concentration as g/ml

How to Test Using Optical rotation Technique

Fill a clean, 100 mm-long polarimeter tube with the diluted/pure essential oil. Put the filled sample tube in the polarimeter and record the measured value. Compare the calculated value with the expected value.

Method 2: Measuring Refractive Index

Another popular technique to analyze the quality of an essential oil, refractive index is a unique number that designates how the oil responds to and bends light.

In simple terms, this purity test is measurement of how the speed of light is altered when passing through the essential oil. The refractive index of essential oil can be compared to that of a reliable sample.

Method 3: Measuring Gravity (Specific Gravity)

The 3rd method includes measurement of essential oil purity using a densitometer.

In this method the density of a particular essential oil is compared with the density of water. Specific gravity readings are measured at certain temperatures and pressures, as these factors can affect the final result.

How to check purity using Specific Gravity?

The essential oils should have a pre-defined range of specific gravity. In case the test results are not in that range then essential oil is considered to be unadulterated and pure.