Corymbia citriodora essential oil: two studies, ISO 3044

What is Corymbia citriodora, botanically?

According to the World Checklist of Vascular Plants (WCVP, Kew), in the extract read on 28/10/2026, Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson is a name of rank “Species” with the status “Accepted”, placed in the family Myrtaceae (identifier 47992). Koribeche et al. (2026) name the plant of their study “Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson”. According to WCVP (Kew), in the extract read on 28/10/2026, Eucalyptus citriodora Hook., a name of rank “Species”, is a synonym (status “Synonym”) whose accepted name is Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson (identifier 47992).

According to the Plants of the World Online (POWO, Kew) entry for the taxon “Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson”, the native range of the species is “Queensland to NE. New South Wales”. The same entry describes Corymbia citriodora as “a tree” that grows “primarily in the seasonally dry tropical biome”.

How did Koribeche et al. (2026) obtain their two oils of Corymbia citriodora?

According to Koribeche et al. (2026), the fresh foliage used came from healthy mature Corymbia citriodora trees growing on the grounds of the National Higher School of Agronomy (ENSA), Algeria (36.7222384° N, 3.1497033° E), and was harvested during the period of active vegetative growth. In this study, the harvested material dried in the shade at ambient laboratory temperature, the dry leaves were then ground, and two parallel extractions were applied to this leaf powder: classical steam distillation (SD) and steam distillation enhanced by microwave irradiation (MSD). For SD, 200 g of plant matter were distilled for 120 min in a Clevenger-type apparatus, at a steam flow of 10 mL·min⁻¹. According to the authors, SD was run with a 1000 W heating mantle, for a total energy of about 2.0 kWh. According to the authors, MSD used the same mass of plant material (200 g), irradiated at 500 W for 20 min under an identical steam flow, for a total energy of about 0.167 kWh. The 20 min duration of MSD was set from a kinetic optimisation that, according to the authors, showed a complete extraction yield due to a rapid microwave-induced glandular rupture. The recovered hydrodistillates were then dehydrated over anhydrous sodium sulfate, transferred into amber glass vials and kept at 4 °C pending analysis.

How did Koribeche et al. (2026) analyse the oils?

The composition of the oil was characterised with a system coupling gas chromatography to tandem mass spectrometry (GC-MS/MS) by means of a triple quadrupole mass analyser. The oil was injected as a 10 % (v/v) solution in hexane (100 µL of oil with 900 µL of hexane), 1 µL at a time, into an injector held at 250 °C, in split mode at a 1:100 ratio. Separation was performed on a fused-silica capillary column 30 m long, with an internal diameter of 0.25 mm and a stationary-phase film thickness of 0.25 µm. The carrier gas was helium, at a constant rate of 1.20 mL/min, equivalent to a linear velocity of 39.4 cm/s. The oven programme began with a 4 min hold at 35 °C, rose at 10 °C/min to 240 °C, then at 8 °C/min to 300 °C, a temperature held for 8 min. Detection used electron ionisation (EI) at 70 eV over 30–500 m/z, with the ion source at 200 °C, the transfer line at 250 °C and a solvent delay of 3.00 min. Compounds were identified by matching the electron ionisation mass spectra against the NIST 20, Wiley 12 and FFNSC 4 databases, and by comparing calculated Kovats retention indices. The principal constituents (citronellal, citronellol, isopulegol, β-caryophyllene) were further confirmed with commercial reference standards. The relative percentages of the constituents were calculated by normalisation of the GC peak areas, assuming equal mass response factors for all volatile components. According to section 2.1 of the study, profiling of the SD and MSD oils identified “sixty-three constituents” for the two oils together, which account for 99.85 % of the total composition of the SD oil. In the same sentence, they account for 99.97 % of the total composition of the MSD oil.

What do Koribeche et al. (2026) report as the main constituent of each oil?

According to section 2.1 of the study, citronellal is the dominant constituent of the SD oil, at 38.24 %. In the same section, citronellal is the dominant constituent of the MSD oil, at 48.41 %. At the end of section 2.1, the authors write that what they report “supports the use of MSD as a greener and more selective recovery technique for the citronellal chemotype”; “citronellal chemotype” is their qualification, with no numerical criterion in the sentence, and “greener and more selective” is their judgement.

How does Table 1 of Koribeche et al. (2026) group the constituents by class?

The “Chemical class summary” of Table 1 gives the following values, in area %, for the SD oil and the MSD oil.

Which compounds does Table 1 of Koribeche et al. (2026) list?

The rows below are those of Table 1 of the study, in its order and with its numbering, with the compound names as the table writes them; the values are relative peak areas (%), one column for the SD oil and one for the MSD oil. Where the table writes “-”, its note defines it as “not detected”. “Isolongifolol” (No. 52) and “(−)Isolongifolol” (No. 63) are two separate rows of the table, each with its own values.

How did Chikhi-Chorfi et al. (2025) obtain their hydrodistilled oil?

According to Chikhi-Chorfi et al. (2025), section 4.1, the leaves of “E. citriodora” were collected “at the same period” as the other species of the study, which was collected in June 2023 (the month follows from “at the same period”), from the botanical garden of the Higher National Agronomic School of Algiers (ENSA); this is the same school, in Algeria, as in Koribeche et al. (2026). The plants were compared to a “voucher” already deposited in the herbarium of the botanical department and authenticated by Pr. Hassen Abdelkrim (“Plant taxonomist”), of the Department of Botany of the “High National Agronomic School”. The essential oil was extracted by hydrodistillation in a Clevenger-type apparatus: 100 g of shade-dried leaves of “E. citriodora” were placed in 2 L flasks containing 1.5 L of distilled water, for 2 h. At the end of the hydrodistillation, the oil was dried over anhydrous sodium sulphate, then stored at 4 °C, protected from light, for the subsequent analyses. In Table 1 of the study, the line “Oil yield % (v/w)” reads 3.45 for this oil, distilled from shade-dried leaves; the table states the “v/w” basis without further detail.

How did Chikhi-Chorfi et al. (2025) analyse the oil?

According to section 4.3 of the study, gas chromatography was performed on a “GC-FID/7890” system fitted with a fused-silica capillary column with an apolar DB 5MS stationary phase (40 m × 0.18 mm × 0.18 μm), programmed from 50 °C (5 min) to 300 °C at 5 °C/min, then held for 15 min at 300 °C. For GC-FID, 2 μL of a 4 % solution of oil in hexane were injected in split mode (ratio 1:100), injector at 280 °C, He carrier gas at 1.3 mL/min, flame ionisation detection at 320 °C; the quantitative data were taken directly from the GC-FID peak areas, without correction factors. GC-MS was performed on an automated system, a 7890 chromatograph coupled to a 5975C mass spectrometer, with an apolar DB 5MS column (40 m, 0.18 mm internal diameter, 0.18 μm film), helium at 1.3 mL/min, a 1:25 split, 0.2 μL injected (diluted 1/10 in hexane, v/v) at 280 °C, the same oven programme as in GC, electron ionisation at 70 eV and masses scanned from 33 to 550 atomic mass units. According to section 4.4, the constituents were identified “tentatively” by comparing their retention indices, determined against a homologous series of C8-C17 n-alkanes injected under the same conditions, with those of the literature; the identification was confirmed by comparing the mass fragmentation spectra with those of the NIST library (225,000 records) and with literature data. According to section 2.1, the chromatographic analysis identified 27 compounds in this sample of “E. citriodora” oil.

Which compounds does Table 1 of Chikhi-Chorfi et al. (2025) list for this oil?

The rows below are those of the “Eucalyptus citriodora” column of Table 1, in its order and with its numbering, with the compound names as the table writes them; the values are GC-FID peak areas (%), without correction factors. Where the table writes “-”, its note defines it as “Not detected”.

The class lines of the same column read as follows.

Which ISO standard covers the essential oil of Corymbia citriodora?

According to its page in the ISO catalogue, ISO 3044:2020 carries the title “Essential oil of Corymbia citriodora (Hook.) K.D. Hill and L.A.S. Johnson (syn. Eucalyptus citriodora Hook.)”. On 21/09/2026, the same page gives ISO 3044:2020 the status “Published”, the publication date 2020-07, the stage “International Standard confirmed” (90.93) and edition 3. According to the abstract on this page, ISO 3044:2020 “specifies certain characteristics of the essential oil of Corymbia citriodora (Hook.) K.D. Hill and L.A.S. Johnson (syn. Eucalyptus citriodora Hook.) with a view to facilitating the assessment of its quality”. In the ISO catalogue, under classification ICS 71.100.60, on 19/03/2026, the entry ISO 3044:1974 carries the mention “[Withdrawn]”, the title “Oil of Eucalyptus citriodora”, stage 95.99 and committee ISO/TC 54. In the same listing, the entry ISO 3044:1997 carries the mention “[Withdrawn]”, the title “Oil of eucalyptus citriodora Hook.”, stage 95.99 and committee ISO/TC 54. In the same listing, on 19/03/2026, the entry ISO 3044:2020 carries the title “Essential oil of Corymbia citriodora (Hook.) K.D. Hill and L.A.S. Johnson (syn. Eucalyptus citriodora Hook.)”, stage 90.93 and committee ISO/TC 54.

See also: drops ↔ ml converter.

References

• Govaerts R. (ed.), World Checklist of Vascular Plants (WCVP), Royal Botanic Gardens, Kew — https://sftp.kew.org/pub/data-repositories/WCVP/wcvp.zip
• Koribeche S., Bertouche S., Sabba N., Sahraoui N., Djelti F., Alkholifi F.K., Al-dossari R.M., Kahaleras M.S., Hani M., Chetbani Y., Karmi Y., Daoudi-Hacini S., « Extraction, Phytochemical Profiling, and Computational Evaluation of Corymbia citriodora Essential Oil as a COX-2 Inhibitor: Steam vs. Microwave-Assisted Distillation, GC–MS/MS, Docking, DFT, and MD Simulations », Pharmaceuticals 2026;19(9):1382, doi:10.3390/ph19091382 — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pmc&id=13610388
• Chikhi-Chorfi N., Haddadj F., Djellout B., Zenia S., Hazzit M., Marniche F., Milla A., Smai A., « Chemical Composition and Insecticidal Activity of Essential Oils from Origanum floribundum and Eucalyptus citriodora Against the Louse Bovicola limbatus », Molecules 2025;30(19):4001, doi:10.3390/molecules30194001 — https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pmc&id=12525578
• International Organization for Standardization (ISO), catalogue record « ISO 3044:2020 — Essential oil of Corymbia citriodora (Hook.) K.D. Hill and L.A.S. Johnson (syn. Eucalyptus citriodora Hook.) », edition 3, 2020-07, archived copy of 21/09/2026 (Internet Archive) — https://web.archive.org/web/20260921103211id_/https://www.iso.org/standard/77267.html
• International Organization for Standardization (ISO), online catalogue, ICS 71.100.60 « Essential oils », archived copy of 19/03/2026 (Internet Archive) — https://web.archive.org/web/20260319152944id_/https://www.iso.org/ics/71.100.60/x/
• Plants of the World Online (POWO), Royal Botanic Gardens, Kew, taxon page « Corymbia citriodora (Hook.) K.D.Hill & L.A.S.Johnson », archived copy of 21/09/2026 (Internet Archive) — https://web.archive.org/web/20260921005402id_/https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:986336-1