Quantitative Analysis of the Composition of Tea Tree Oil

Luigi Mondello,¹ Danilo Sciarrone¹ and Margit Geissler,²

¹ Dipartimento Farmaco-Chimico, University of Messina, Italy, ² Shimadzu Europa GmbH, Duisburg, Germany.

Introduction

Essential oils are complex mixtures comprising of many different components. Single components have a special chemical effect, but the sum of all compounds characterizes an essential oil. The composition of the essential oil depends on the climate and soil in which a plant grows. The amount of a compound can even vary from year to year.

Tea Tree Oil

Tea tree (Melaleuca alternifolia) oil is an essential oil that is steam distilled from the leaves of the tea tree, native to Australia. The oil has fresh and pleasant odour, and some medical properties of odour eliminating as well as antibacterial and antiseptic action. Historically, the leaves were used as a substitute for tea, which is how tea tree oil got its name.

Tea tree oil components will vary depending on the growing environment including air and sunlight conditions.

Tea tree oil has found increasing use in certain consumer products including cosmetics. A number of recent dermatological publications indicate that the neat oil has a potential to induce and elicit skin allergies. Dilute solutions have a weaker sensitization potential. As the European Cosmetic Toiletry and Perfumery Association (COLIPA) recommends keeping tea tree oil content in industrial commodities at 1% or below, strict quality control is required.

Heart-cut Multidimensional GC–MS

Due to the complexity of the samples, tea tree oil in this application was analysed using Heart-Cut Multidimensional GC–MS.

Complex samples often cannot be completely characterized by a conventional GC–MS analysis using one single column. Either the matrix content of the sample is too high or the compounds cannot be separated on one column as they are too similar (e.g., optical isomers).

In this case, the use of a second column can solve the separation problem. In the MDGC-2010 system, compounds that could not be separated in the first chromatographic system are transferred to a second capillary column with a different separation mechanism. In this way, two compounds co-eluting on the first column can be identified and quantified on the second column independently of each other. Effectively, the peak capacity of the chromatographic system is increased.

In contrast to traditional heart-cut systems, the MDGC-2010 GC–MS system allows several cuts without showing any shifts of retention times. The user only needs to run one chromatogram to fix all the cut times. Method development for target compound analysis in difficult samples becomes very easy:

• run the standard on the first column (1 run only)

• determine the cut times (unlimited number of cuts)

• run the sample

Analytical Conditions

Tea tree oil diluted 1–10

GC — 1

Column: SLB-5MS 30 m × 0.25 mm i.d. × 0.25 mm f.t. (Supelco, Milan, Italy)

Column head pressure: 200 kPa, helium (constant mode), auxiliary pressure (APC) — 130 kPa, helium

Oven temperature programme: from 50 °C to 280 °C at 3 °C per minute, transfer line — 180 °C

Detector FID (310 °C), H₂: 40.0 mL/min, air: 400.0 mL per minute, sampling rate: 80 msec (12.5 Hz)

GC — 2

Column: SUPELCOWAX 30 m × 0.25 mm i.d. × 0.25 mm f.t. (Supelco, Milan, Italy)

Temperature programme: 50 °C for 10 minutes to 280 °C at 3 °C per minute

Detector: MS, ion source: 200 °C, interface temp.: 220 °C, Interval scan: 40–400 m/z, scan speed: 5000 amu per second (12.5 Hz).

Figure 1

Quantification in Heart-cut MDGC

A calibration curve using standard samples with different concentrations can be acquired using the same conditions and transfer times to the second column.

Table 1

Software for Heart-cut MDGC

All parameters of the system are controlled by the MDGCsolution software. With this software the user can load the monitor chromatogram from FID and graphically determine the cut times for the subsequent MDGC analysis (Figure 1).

Figure 2

Results

In this application note the analysis of tea tree oil using Shimadzu's MDGC-2010 system is shown. Figure 2 shows that sharp peaks of each component in tea tree oil can be obtained using the MDGC-2010 system. In Table 1 the distribution of each component in the tea tree oil is given. Table 2 shows the results of the analysis of the tea tree oil sample in Figure 2. The quadrupole mass spectrometer used for detection in the second dimension ensures a secure identification and characterization of the tea tree oil sample.

Table 2

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