Capillary columns in series for the gas chromatographic analysis of essential oils

Summary By connecting capillary columns of different polarity in series and by changing the temperature program gradient, a system of variable polarity is obtained. The working conditions can be adjusted to optimize separations of complex mixtures. Application to the analysis of essential oils of: lavender, thyme, lemon petit grain, bergamot, and tangerine, are reported.Dedicated to Prof. Dr. A. Liberti on the occasion of his 70th birthday.     

Multidimensional Capillary GC-GC for the Analysis of Real Complex Samples. Part IV. Enantiomeric Distribution of Monoterpene Hydrocarbons and Monoterpene Alcohols of Lemon Oils

This paper describes a fully automated, multidimensional, double-oven GC-GC system, developed in our laboratory. The system is based on the use of mechanical valves which allow the multitransfer of different fractions during the same GC analysis and the use of the two GC independently when the multitransfer options is not used. Pneumatic and electronic circuits permit maintenance of constant retention times in the pre-column, even for the components eluted after numerous transfers. The system has been used for the determination of the enantiomeric distribution of β-pinene, sabinene, limonene, linalol, terpinen-4-ol, and α-terpineol in lemon oils. The results obtained allowed the characterization of cold-pressed lemon oils.     

Limonene concentration in lemon (Citrus volkameriana) peel oil as a function of ripeness

The dependence of the limonene content of lemon (Citrus volkameriana) peel oil on the degree of ripeness of the fruit has been studied by using steam distillation and cold pressing to extract the oils from lemon fruit peel at different stages of maturation (green, greenish-yellow, and yellow-orange peel coloration). Samples of essential oils were analyzed by high resolution GC and GC-MS, using tetradecane as internal standard for quantitation. Forty components were detected; thirty eight were positively identified by comparison of their mass spectra (El, 70 eV) and Kováts retention indexes (determined using a non-logarithmic scale on capillary columns coated with both polar (DB-Wax) and non-polar (DB-1) stationary phases) with those of standards and with data reported in the literature. The limonene concentration reached a maximum level of 79.4% when the fruit was in the intermediate maturation stage characterized by greenish-yellow coloration.     

Fast headspace analysis with short microcapillary columns

Summary A new method of analysis using headspace gas chromatography with microcapillary columns is proposed. Small diameter (50 μm I.D.) fused-silica capillary columns with non-extractable SE-54 and PS-255 polysiloxane stationary phases were used for the analysis of low boiling organic compounds. The small diameter columns possess the usual very high efficiency so that the method can be employed for the headspace analysis of complex mixtures. The use of short microcolumns reduces the analysis times in comparison to conventional capillary columns. Good performances were obtained in the analysis of volatile compounds in some lemon essential oil, perfumes, and water samples.     

Determination of petitgrain oils landmark parameters by using gas chromatography–combustion–isotope ratio mass spectrometry and enantioselective multidimensional gas chromatography

Gas chromatography–combustion–isotope mass spectrometry was employed for the assessment of the Carbon isotope ratios of volatiles in Italian mandarin and lemon petitgrain oils. In addition, the composition of the whole oil and the enantiomeric distribution of selected chiral compounds were determined for all the samples by using gas chromatography and by multidimensional and conventional enantioselective gas chromatography. The composition of the oils was compared with previous studies. The enantiomeric distribution of lemon petitgrain oils is here reported for the first time. On the composition of mandarin petitgrain oil, the information available in literature, to date, is relative only to one sample from Egypt. Carbon isotope ratio of several terpene hydrocarbons and of their oxygenated derivatives contained in petitgrains was compared with the δ ¹³C_VPDB values of the same compounds present in the corresponding genuine Italian Citrus peel oil. The results prove that the isotopic values obtained for lemon and mandarin petitgrain oils are very close to those relative to the corresponding peel oils determined in previous studies.     

Authenticity control of essential oils containing citronellal and citral by chiral and stable-isotope gas-chromatographic analysis

Enantioselective capillary GC on a Supelco β-DEX 225 column (heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin SPB 20poly—20% diphenyl, 80% dimethylsiloxane) and isotope-ratio mass spectrometry, coupled online with capillary GC on an HP5 column have been used for origin-specific analysis and authenticity control of essential oils, for example lemon (Citrus limon), lemongrass (Cymbopogon citratus and Cymbopogon flexuosus), citronella (Cymbopogon nardus L.—Ceylon type and Cymbopogon winterianus—Java type), Litsea cubeba, Lippia citriodora, lemon myrtle (Backhousia citriodora), lemon gum (Eucalyptus citriodora), and, especially, precious lemon balm oil (Melissa officinalis L.). Isotope data (δ¹³C_PDB and δ²H_V-SMOW) for citral (neral + geranial) and citronellal from on-line GC–C/Py–IRMS and chiral data for citronellal in these essential oils are reported. The possibility of using these data to determine the origin of these essential oils and to detect adulteration is discussed. Principal-components analysis (PCA) of specific compounds in two essential oils of lemongrass and Litsea cubeba was performed as a practical statistical method for distinguishing between these two types of oil.     

Dynamics of the accumulation of the monoterpenoids ofCitrus limon

The amounts and compositions of the essential oils in the leaves and fruit of Meyer's lemon in the various vegetation periods have been studied. It has been established that as the fruit ripens the amount of essential oils and of monoterpene hydrocarbons in its peel and in the leaves increases.     

Lemon Oils Attenuate the Pathogenicity of Pseudomonas aeruginosa by Quorum Sensing Inhibition

The chemical composition of three Citrus limon oils: lemon essential oil (LEO), lemon terpenes (LT) and lemon essence (LE), and their influence in the virulence factors production and motility (swarming and swimming) of two Pseudomonas aeruginosa strains (ATCC 27853 and a multidrug-resistant HT5) were investigated. The main compound, limonene, was also tested in biological assays. Eighty-four compounds, accounting for a relative peak area of 99.23%, 98.58% and 99.64%, were identified by GC/MS. Limonene (59–60%), γ-terpinene (10–11%) and β-pinene (7–15%) were the main compounds. All lemon oils inhibited specific biofilm production and bacterial metabolic activities into biofilm in a dose-dependent manner (20–65%, in the range of 0.1–4 mg mL⁻¹) of both strains. Besides, all samples inhibited about 50% of the elastase activity at 0.1 mg mL⁻¹. Pyocyanin biosynthesis decreases until 64% (0.1–4 mg mL⁻¹) for both strains. Swarming motility of P. aeruginosa ATCC 27853 was completely inhibited by 2 mg mL⁻¹ of lemon oils. Furthermore, a decrease (29–55%, 0.1–4 mg mL⁻¹) in the synthesis of Quorum sensing (QS) signals was observed. The oils showed higher biological activities than limonene. Hence, their ability to control the biofilm of P. aeruginosa and reduce the production of virulence factors regulated by QS makes lemon oils good candidates to be applied as preservatives in the food processing industry.     

Applications of the O-FID oxygenes analyzer in the cosmetic industry

Summary The application of the O-FID Oxygenates Analyzer developed for the selective determination of oxygenated compounds in modern fuels has been studied for the identification and characterization of essential oils. In comparison to FID detection the O-FID technique results in a much simpler chromatogram. Because of the high selectivity for oxygenated compounds the O-FID method offers a fast and reliable quality control and positive identification of samples of different origin. Chromatograms obtained for lavender oils of different origin, natural and synthetic lemon oils and oils of bergamot respectively, as well as for camomilla oils are presented.     

Analysis of pesticide residues in essential oils of citrus fruit by GC–MS and HPLC–MS after solid-phase extraction

A robust reliable method for the analysis of residues of pesticides in citrus groves was developed. Residues of twelve pesticides were extracted from citrus essential oils by SPE, separated by liquid chromatography and analyzed by GC-MS. In addition, ten pesticides were extracted by SPE, separated and analyzed by electrospray HPLC-MS. In the case of lemon essential oils, all twenty residues were separated by liquid/solid extraction on a mixed Florisil-C(18) cartridge. The method enabled the analysis of the twenty pesticide residues at levels of 2 to 30 ppm with limits of detection ranging between 0.02 to 0.50 mg L(-1).     

Sicilian lemon oil: Composition of volatile and oxygen heterocyclic fractions and enantiomeric distribution of volatile components

A total of 92 samples of Sicilian lemon oils (Citrus limon (L.) Burm. f.) produced from September 2008 to June 2009, industrially cold-pressed by different extraction techniques (Brown Oil Extractor and Food Machinery Corporation), were analyzed by GC-flame ionization detector (FID) and GC/MS-LRI to investigate the volatile fraction; by RP-HPLC/PDA to determine the non-volatile components and by enantio-GC-FID to determine the enantiomeric ratios of 12 volatile components. This study provides a detailed investigation on the composition of Sicilian lemon essential oils industrially produced during a productive season, with the aim to recognize quality parameters for the characterization of this product. The results obtained are discussed to evaluate seasonal variation, influence of the extraction techniques, and are compared with those obtained for samples produced during different seasons.     

Conventional inner diameter short capillary columns: an approach to speeding up gas chromatographic analysis of medium complexity samples.

Short capillary columns (5 m) with 0.25 mm inner diameter (I.D.) are applied to the GC analysis of medium complexity samples (up to 30 components) with the aim of shortening analysis time. This approach is complementary to fast GC with narrow-bore columns and is based on compensating the lower efficiency of short columns with conventional I.D.'s (0.25-0.32 mm) by using a stationary phase selectivity suitable to separate the components of the sample under investigation, so that the required resolution power is achieved but, at the same time, the analysis time is shortened. The qualitative and quantitative effectiveness of this approach is demonstrated through the analysis of: essential oils with different compositions (chamomile and rosemary), low-volatility triterpenes in a plant extract (Maytenus aquifolium and M. ilicfolium), thermolabile pyrethrins in a Pyrethrum extract, and a mixture of pesticides applied to protect medicinal plant crops. In all examples, GC analysis was five to ten times faster than with conventional columns.     

Direct resistively heated column gas chromatography (Ultrafast module-GC) for high-speed analysis of essential oils of differing complexities

This study applies Ultrafast module-GC (UFM-GC) with direct resistively heated columns to routine analysis of a group of essential oils of differing complexities (chamomile, peppermint, rosemary and sage). Essential oils were analysed by conventional GC with conventional inner diameter (i.d.) columns (0.25 mm) of different lengths (5 and 25 m long) and by Fast GC and Ultrafast module-GC with narrow bore columns (0.1 mm i.d., 5 m long). Column performance were evaluated and compared through their Grob test, separation number and peak capacity. Ultrafast module-GC was successful in the qualitative and quantitative analysis of essential oils of different compositions with analysis times between 40 s and 2 min versus 20-60 min required by conventional GC. Critical pairs or groups of components were separated by carefully tuning selectivity of the stationary phase to compensate for loss of efficiency due to the use of short columns and high temperature rates. The Ultrafast module-GC results of peppermint e.o. analyses were also validated and compared to those obtained by conventional GC; by measuring precision over time (i.e. repeatability and intermediate precision) and accuracy. Ultrafast module-GC showed a good separation reproducibility affording reliable component identification through the relative retention times and quantitative determination through normalised peak areas. Accuracy data also showed that Ultrafast module-GC and conventional GC normalised areas and areas percentage were perfectly comparable.     

Six Common Herbs with Distinctive Bioactive,Antioxidant Components. A Review of Their Separation Techniques

Rosemary, oregano, pink savory, lemon balm, St. John’s wort, and saffron are common herbs wildly grown and easily cultivated in many countries. All of them are rich in antioxidant compounds that exhibit several biological and health activities. They are commercialized as spices, traditional medicines, or raw materials for the production of essential oils. The whole herbs or the residues of their current use are potential sources for the recovery of natural antioxidant extracts. Finding effective and feasible extraction and purification methods is a major challenge for the industrial production of natural antioxidant extracts. In this respect, the present paper is an extensive literature review of the solvents and extraction methods that have been tested on these herbs. Green solvents and novel extraction methods that can be easily scaled up for industrial application are critically discussed.     

Determination of tocopherols in vegetable oils by CEC using methacrylate ester-based monolithic columns

The separation and determination of tocopherols (Ts) in vegetable oils by CEC using methacrylate ester-based monolithic columns has been developed. The effects of pore size of the monolithic columns were studied, and the composition of mobile phase was optimized. The optimal pore size of the monolith was obtained with 12 wt% 1,4-butanediol in the polymerization mixture. Excellent resolution between tocopherols was achieved within 10 min analysis time with a 99:1 v/v MeOH-aqueous buffer containing 5 mM tris(hydroxymethyl)aminomethane at pH 8.0. The LODs were lower than 2.3 microg/mL, and interday and column-to-column reproducibilities at 25 microg/mL were better than 5.6%. Using a 93:7 v/v MeOH-aqueous buffer, both tocopherols and tocotrienols (T(3)s) of grapeseed and palm oils were resolved. Application to the detection of olive oil adulteration with low-cost edible oils was demonstrated.     

Determination of the volatile compounds of vegetable oils using an ion-mobility spectrometer

An analysis of olive, pressed sunflower, extracted sunflower, extracted soybean, deodorized sunflower, deodorized rapeseed, and deodorized corn vegetable oils has been performed on an FlavourSpec® ionmobility spectrometer. Twenty-four compounds were found in the spectra of the gas phase above samples of vegetable oils and 12 of them were identified. Ion-mobility spectrometry combined with polycapillary chromatography columns made possible distinguishing oils from different plants, as well as pressed and extracted sunflower oil by the volatile components found in the gas phase above the oil.     

Spectrophotometric Estimation of Citral in Essential Oil

Citral forms an important constituent of many essential oils. It is present in a large number of essential oils containing lemon perfume and is of great commercial value. Methods of estimation of citral, available in literature are not very accurate or time consuming. The method developed by the author is based on colour change reaction of citral with rhodium (III). If all necessary requirements for experiment are ready, the estimation of citral occures within ten minutes. Rhodium (III) can also be determined with its colour change reaction by citral.     

Column Chromatographic Procedure for the Determination of Polychlorinated Biphenyls in Certain Industrial Oils

Abstract

Certain oils cause considerable interference in the determination of PCBs by gas chromatography with electron capture detection, requiring time-consuming sample clean-up procedures. Column chromatography, using small, radially-compressed silica columns, is used to isolate PCBs in various oil matrices, thus permitting quantitative analysis. Pure mineral oil, phosphate ester, glycol-base, and sulfonated mineral oils were studied.     

Rapid preliminary separation of petroleum hydrocarbons by solid-phase extraction cartridges

Small, prepacked columns are tested for fractionating petroleum hydrocarbons from crude oil and products oils. Both normal-phase (silica) and reversed-phase (C₁₈) stationary phases yielded fast, easy, and reproducible separations, which facilitated further analysis of the oils by gas or liquid chromatography and mass spectrometry. The different separation characteristics of the stationary phases offer great flexibility in fractionating oil, enriching special compound classes, or separating hydrocarbons from environmental matrices.     

Qualitative Analysis of Citrus Fruit Extracts by GC/MS: An Undergraduate Experiment

Rinds from a variety of citrus fruits (grapefruit, lemon, lime, navel and Valencia orange, tangerine, and tangelo) were extracted and analyzed using GC/MS. In this experiment, sophomore organic chemistry students explore extraction techniques and gas chromatography with mass spectrometry detection as well as the theory associated with these methods. Furthermore, the experiment provides students with an opportunity to learn about essential oils and terpenes. Background information on terpenes, the extraction protocol, and GC/MS conditions used for analysis is provided. A summary is given of the most frequently observed terpenes and terpenoids identified for each citrus fruit mentioned above.