Dear Researchers,

GC and GC-MS instruments equipped with columns of similar stationary phases (polar or non-polar) are used worldwide for essential oil (EO) analysis. Retention Index (RI) and mass spectrum (MS) of the EO constituents should match with literature/online library data.

However, in some cases components have similar mass and very close retention index (RI) on a particular column. In such cases, support of other method(s) became necessary for confirmation of the identity. Determination of RI on a column having other polarity may be a very useful method for confirmation. Some authors used two columns (one polar and other non-polar) for RI determination along with GC-MS for routine EO analyses.

Inspite of wider acceptance, identification of EO constituents using GC and GC-MS methods is considered ‘tentative identification’.

Addition of NMR and/or IR data to the above would strengthen the results.

Regards,

RS Verma

Dear Ganesh

I appreciate your response, but what about HPLC or LC-MS or GC-MS-MS and other techniques?

Best wishes.

Dear Sir,

Looking at the work done by Weyerstahl et al. (Constituents of commercial Labdanum oil, Flav. Fragr. J. 13, 295-318, 1998 or Constituents of the essential oil of Achillea eriophora DC., Flav. Fragr. J. 12, 71-78, 1997) or Cavalli et al. (Chemical variability of the EO of Helichrysum faradifani Sc. from Madagascar, Flav. Fragr. J. 2006, 21, 111-114 for example) you will find examples of EO constituents identification through GC/MS and NMR analysis following liquid-liquid extractions or flash chromatogry purification. NMR analysis (13C NMR spectroscopy) can also be used directly on crude oils (see for example Mariotti et al. Composition of the EO of Cistus ladaniferus L. cultivated in Corsica (France), Flav. Fragr. J. 12, 147-151, 1997).

Best regards.

The standard technique for analysis of constituents of essential oils is gas chromatography, coupled or not with MS, due to the volatile nature of the components of the oil.

Dear Emeline

Thank you for your information. This is what I am looking for. Do you have more such references?

Best wishes.

Dear Nelson

Yes, I am aware of that. In addition to the well-known techniques, what are the other techniques developed recently? Can you throw some light on this aspect?

Thank you for your response.

Best wishes.

GC-FID coupled to MS seem to be widely accepted means of identifying essential oil constituents. Due to their volatility, the choice of methods has to take into consideration of not denaturing or loosing the constituents in any sample being analyzed.

Hello,

The best methods for identification and quantification of essential oil components is CPG/ MS. but HPLC is for  aqueous or organic extract.

Dear Aboaba and Fatima

Thank you for your participation and sharing your informative views on the subject. I am looking for any latest developments in phytochemical analysis and identification other than the widely employed techniques. The problem is that the information published in non-English journals is not accessible and understandable. This is a forum where fortunately we have members from non-English speaking countries.

As far as HPLC is concerned, some of the essential oil constituents (polar, oxygenated constituents) are water-soluble and escape into the distillation water stream during distillation of aromatic crops. This fraction of essential oil rich in organoleptically important constituents is generally lost as the distillation water is discarded (for more details you can see some of my publications on the subject). The investigations carried out so far isolated the constituents/essential oil from the distillation water and examined the composition employing GC-FID and GC-MS. No one (as far as I know) so far attempted HPLC route for the analysis of this water with essential oil constituents.

best wishes.

Dear Friends

The essential oil constituents exist in 2 forms namely, the free (as components of the essential oil) and the bound (to glycosides) forms. I saw a recent article on the isolation and analysis of the 2 forms in curry leaf (Murraya koenigii):

Free and Glycosidically Bound Volatiles in Curry Leaves (Murraya koenigii) (L) Spreng authored by K. P. Padmakumari published in Journal of Essential Oil Research, 20:6, 479-481, DOI: 10.1080/10412905.2008.9700063.

I am adding the abstract of this paper:

Free and glycosidically bound aroma compounds from Murraya koenigii (L.) Spreng, were isolated and separated by Amberlite XAD-2 column. The fraction containing the free aroma compounds was eluted with pentane: diethyl ether (1:1). Aroma compounds from the bound fraction were released by β-glucosidase hydrolysis. Samples were analyzed by GC and GC/MS. Sixty-seven constituents were found to be present in the bound fraction where linalool was found to be the main constituent. In the free aroma fraction, seventy-eight constituents were present with octyl acetate being found as the main constituent. In the hydrodistilled oil, fifty-six compounds were identified and β-caryophyllene was the main compound.

I am sharing this information with all of you hoping that you may add new information on essential oils isolation and identification of its constituents.

Any comments? suggestions?

Best wishes.

Dear Friends

This is another interesting publication though not directly connected to the query:

Shankaranarayana, K.H. and Kamala, B.S. 1989. Six new essential oils from waste plant material. Indian Perfum. 33: 40-43.

The authors re-distilled previously distilled material in Clevenger apparatus by adding acid to the Clevenger water and recovered essential oils from the distilled waste.

Best wishes.

Based on my experienced, GCMS is a good instrument but it is necessary to perform derivatization using BSTFA or MSTFA to obtain good separation.

Dear Andi Suhendi

I appreciate your participation in the discussion. Can you please add brief details of BSTFA and MSFTA for the benefit of young RG friends who are not conversant with these techniques?

Best wishes.

Essential oil is extracted from plant material by hydro distillation in a Clevenger-type apparatus. A sample of the EO is dried over anhydrous sodium sulphate. The EO component analysis is performed by gas chromatography (GC) and gas chromatography/mass spectroscopy (GC/MS) using the adequate instrumentation. The operating conditions should be selected from the literature. Compounds in the chromatograms are identified by comparison of their mass spectra with those in the database (NIST 2008 library or other), and by comparison of their calculated retention index with those reported in the literature (Adams,2007), for the same type of column. Always is necessary to use commercial standards, when available.

Dear Alejandro Urzua

Thank you for providing a detailed response describing all the important steps in the identification of essential oil constituents. In addition to retention indexes and mass spectra, peak enrichment through co-injection of authentic samples is also practiced.

Best wishes. 

Dear Dr. Rao there were affordable and easy methods can be applied in low scale industry or low budget reasearch like the determination of the distinctive physical chracter such as weiht per ml at 20 C, refractive index and optical rotation.

beside that TLC provide alternative for GC or me be used in compination for analysis of fraction seperated by GC. on other han TLC is the method of chice for less volatile sesquiterpenoids

Dear Ahmed Sabir

Physico-chemical properties of essential oils do not provide information on the chemical composition of the essential oil i.e. how many compounds the essential oil contains? Which compounds the essential oil has and their relative percentages or quantities in the essential oil?

Thank you for your views.

Best wishes.

The best methods for essential oil analysis are GC ans GC/MS, Of course with calculation of retention indices. I think  the glycoside compounds. can not be evaporated by steam distillation and do not exist in essential oils

Dear Fatemeh Sefidkon

Thank you for your views on the subject. As far as the glycosidically bound volatile compounds are cocerned you may see the publication of Dr. K. P. Padmakumari published in Journal of Essential Oil Research. I have given the abstract and details of this publication in one of my previous posts.

Best wishes.

Dear Researchers,

GC and GC-MS instruments equipped with columns of similar stationary phases (polar or non-polar) are used worldwide for essential oil (EO) analysis. Retention Index (RI) and mass spectrum (MS) of the EO constituents should match with literature/online library data.

However, in some cases components have similar mass and very close retention index (RI) on a particular column. In such cases, support of other method(s) became necessary for confirmation of the identity. Determination of RI on a column having other polarity may be a very useful method for confirmation. Some authors used two columns (one polar and other non-polar) for RI determination along with GC-MS for routine EO analyses.

Inspite of wider acceptance, identification of EO constituents using GC and GC-MS methods is considered ‘tentative identification’.

Addition of NMR and/or IR data to the above would strengthen the results.

Regards,

RS Verma

Dear Verma

Thanks for your detailed post. Have you tried co-injection with authentic samples? Can you throw some light on LRI and KI?

Best wishes

GC using the retention Indices (Kovac Indices; alkanes used for standardisaton; see literature) is a suitable method. When doing so, use the Kovac Indices on two different colums, a more polar one and an apolar one. When sou only use one column, you should have the GC couples with a MS. So you either have the Kovac Indices on two different columns or those on one column and the molecular weights for sound identification.

Dear Prof. Adolf Nahrstedt

Thank you for your informative response.

If you are not able to use the GC or GC-MS in your lab, or nearby, try to TLC plates that may separate some constituents. But to identify the structures, you may still need to be analyzed by GC-MS, or LC-MS, as well as some other chemical analytical methods fue to the complex of the structures.

Dear Dr. Zhu

Can you provide more details about LC-MS identification/authentication of essential oil constituents?

Best wishes.

LC-MS methods only apply to those compounds that are not volatile or semi-volatile that sometimes GC-MS can not handle them. I assume that you can find quite a lots of reference, especially in new drug discoveries. I do not have any specific paper that can refer.

Dear Dr. Zhu

Thank you for your useful information.

Dear Sir,

I only had one more reference in my archives, but perhaps should you try to contact directly this team ?

Cavalli, J.F., Tomi, F., Bernardini, A.F. and Casanova, J., 2003. Composition and chemical variability of the bark oil of Cedrelopsis grevei H. Baillon from Madagascar. Flavour Fragr. J. 18, 532-538.

Best wishes

Sir,

Co-injection with authentic  compound is one of the very useful technique for identification of essential oil constituents. It is widely / frequently exercised by  essential oil analysts.

Dear Emeline and Verma

Thanks for your informative posts.

Analysis (by GC-MS and/or GC-FID) of optically active enantiomers found in many essential oils can also assist. The Australian TTO industry has developed these to test for adulteration for two compounds (terpinen-4-ol and alpha-terpinene) with good success.

The ratio of optically active enantiomeric constituents of essential oils is an important topic that has not been fully explored. Initial papers on the subject appeared in the 1990s but did not ignite the interest of researchers. Classical analysis of essential oils is still the hot topic of researchers.

Dear @ Dr. Tony, thank you for your interesting post on the adulteration detection in essential oils. In India, colorimetric procedures were developed in the 1960s for adulteration detection before the advent of GC-FID and GC-MS.

Dear friends

Here is an interesting discussion on LinkedIn initiated by Christine Carson:

Phthalates contamination in essential oil

"Have you ever seen phthalate compounds listed in your compositional analysis results for an oil? If so, you need to know phthalates shouldn't be in your essential oils. They are not natural constituents of essential oils but easily get into them during extraction (especially during supercritical CO2 extraction), processing and storage. Contact with phthalate-containing plastics is the most likely source of phthalates in essential oils.

The interesting blog post below discusses some of the related points and I would add that diethyl phthalate is not known to occur naturally. If its in your oil, its a contaminant." Christine Carson

Well we need to look into this problem more closely and devise techniques to detect the contamination in different essential oils. This opens a new window for new research opportunities. 

Thanks to you Christine,

This is an interesting topic that shouldn't be overlooked,

Several studies suggest that DEP can cause nervous system damage as well as to the male and female reproductive organs.

more so, Hormonal imbalance and likable birth defects has been linked to high dosage of certain phthalates in the studies of rodents.

GC method is the best especially when coupled with mass spectrometer

Dear Uchenna and Dahiru

Thanks for your interest in the topic and your useful responses.

Good luck