Automated on‐line HPLC‐HRGC with gradient elution and multiple GC transfer applied to the characterization of citrus essential oils

Abstract

Citrus essential oil analysis is characterized by the complexity of the separation of all the components which may belong to different classes of compounds and be present in a wide range of concentrations. Capillary GC is the best technique for characterizing the volatile fraction of citrus essential oil. In many cases, however, this technique does not achieve complete separation of all the components. A combination of LC and HRGC in off‐line methods is necessary to achieve complete resolution of the minor components present in the oil and in general to facilitate the identification of the components belonging to different classes. Very recently we have demonstrated the possibility of using on‐line HPLC‐HRGC coupling for fractionation and identification of alcohols in lemon oils. In the present work, a fully automatic HPLC‐HRGC instrument was used for the pre‐separation of the essential oils into the various classes of compounds, using gradient elution and multiple fraction transfer into the capillary column. This method allowed a pre‐separation of the components into four major classes of compounds: hydrocarbons, aldehydes, esters, and alcohols before their transfer into the GC. A good correlation with the existing off‐line methods was found. The ability of the Instrument to perform, In a fully automatic way, HPLC pre‐separation with gradient elution and GC transfer of more than one fraction from a single HPLC injection, was found to be very useful for routine characterization of various essential oils.

Advanced and innovative chromatographic techniques for the study of citrus essential oils

“…This technique was first applied to citrus essential oil analysis by Munari et al in 1990. 53 In a later study, on-line LC-GC coupled with Fourier transform infrared spectroscopy (FTIR) was used as a sensitive approach for the determination of citropten and bergapten in a bergamot oil sample.…”

“…53 In a later study, on-line LC-GC coupled with Fourier transform infrared spectroscopy (FTIR) was used as a sensitive approach for the determination of citropten and bergapten in a bergamot oil sample. 54 Figure 9 illustrates (a) the HPLC separation of the bergamot oil, (b) the GC separation of the target analytes employing FID, and (c) FTIR detection.…”

Automated LC‐GC: A powerful method for essential oils analysis. Part IV. Coupled LC‐GC‐MS (ITD) for bergamot oil analysis

“…have been outlined in many publications [ 12, and, in comparison with off-line methods, it offers a number of advantages: the amount of sample required is much lower; no sample work-up, evaporation, or dilution is needed when liquid samples are analyzed; and very complex sample pre-treatment is possible in a fully automated way. The analysis of essential oils presupposes transfer via a retention gap [22-251 because such samples contain volatile components requiring analysis temperatures starting at 45°C.…”

“…The simple mixtures thus obtained are easier to resolve without problems of peak overlap. It has been shown that the use of grade I1 activity neutral alumina as adsorbent, and light petroleum, light petroleum/diethyl ether, and diethyl ether as eluents [12] permits better fractionation of the essential oils into compound classes (hydrocarbons, esters, carbonyl compounds, and alcohols) than other systems such as distillation or preparative gas chromatography [ Figure 1. Schematic of the LC-Gc-MS inte@ace.…”

2, 5-Dihydroxybenzohydrazide as Electroactive Labeling Reagent for Aliphatic Aldehydes by High Performance Liquid Chromatography with Electrochemical and Ultraviolet Detection

“…The determination of carbonyl compounds in analytical chemistry is becoming always more important for the monitoring of formation reactions or the transformation of aldehydes [ l ] and for the study of the fractions of the volatile compounds responsible for the organolectic characteristics of natural aromas and flavoring agents [2,3].…”