LC-GC analysis of the aromatics in a mineral oil fraction: Batching oil for jute bags

Aromatics of a C₁₅? C₃₀ mineral oil fraction, the “batching oil” used for producing jute fabrics, were analyzed for estimating the toxicity of oil transferred from jute bags to foods. Group-type pre-separation according to ring systems occurred on a LC NH₂ column with pentane and small additions of methanol as eluent. LC fractions were characterized by LC-GC-MS and quantitated by LC-GC-FID. The oil contained 23% aromatics and 1% “polars”; some 99.5% of the aromatics were alkylated.     

Early solvent vapor exit in GC for coupled LC-GC involving concurrent eluent evaporation

Use of early solvent vapor exits for concurrent eluent evaporation with the loop-type interface has two purposes: protection of the GC detectors from large amounts of solvent vapors and more efficient discharge of the vapors to accelerate eluent evaporation and help avoiding broad solvent peaks. Use of a retaining pre-column after the uncoated pre-column can rule out losses of solute materials that form sharp peaks.     

On-line HPLC-HRGC coupling and simultaneous transfer of two different LC fractions: Determination of aliphatic alcohols and sterols in olive oil

A modified loop-type interface is decribed which uses two 6-way valves and concurrent eluent evaporation to perform an on-line transfer and simultaneous gas chromatographic analysis of two different fractions pre-separated by liquid chromatography. The interface is used to simultaneously analyze aliphatic alcohols and sterols present in olive oil. LC pre-separation is carried out using a normal phase column (20 cm × 0.21 cm i.d.) and hexane-isopropanol (99:1) as a mobile phase at a flow of 0.2 ml/min; for the GC analysis a 5 % phenyl, 95 % dimethyl siloxane (25 m × 0.32 mm i.d., 0.4 μm film thickness) column is used.     

Application of coupled LC-GC to the analysis of the polar fraction of diesel particulate matter

Emissions from diesel engines contain mutagenic compounds, many of which are derivatives of polycyclic aromatic hydrocarbons. The complexity of extracts of particulate matter requires multi-stage chromatographic analysis performed off-line. In this study, coupled LC-GC is presented as an alternative method for the analysis of the polar fraction of extracts of diesel particulate matter. Preseparation of the sample was achieved by normal phase HPLC and fractions were transferred to the GC through an on-column interface. Through selective transfer, extensive characterization of the extract is possible and chromatograms can be greatly simplified, thus aiding identification.     

Determination of acylglycerols in vegetable oil methyl esters by on-line normal phase LC-GC

An on-line LC-GC method for the analysis of mono-, di-, and triacylglycerols in vegetable oil methyl esters has been developed. The concentrations of these components have turned out to be key parameters for the quality of diesel fuel substitutes. Separation of all classes of acylglycerols from the fatty acid methyl ester matrix is achieved by LC after acetylation of the hydroxyl groups. The acylglycerol fraction is transferred on-line to GC, using the loop-type interface and concurrent eluent evaporation. Quantification of mono-, di-, and triacylglycerols is performed by combining external calibration with internal standardization. Both recovery of the procedure and reproducibility of the quantitative results are evaluated.     

Characterization of fuel samples by on-line LC-GC with automatic group-type separation of hydrocarbons

Characterization of fuels by LC-GC is possible by use of automatic successive transfer (multiple transfer) of HPLC fractions to a GC via an on-column interface. This paper describes the instrumentation and the methodology for the HPLC separation of the hydrocarbons (aliphatic and aromatic) into separate groups and the on-line transfer of these groups to a capillary GC column. Two HPLC methods were used with the same valve configuration: single column (silica) with column back-flush to detector; and double column (silica and amino-bonded silica) with multiple fraction transfer and back-flush. The first method was used for the analysis of total saturated compounds and total aromatic compounds; the second was used for the separation of the one-, two-, three-, and four-ring aromatic compounds present in diesel fuels. Examples are shown of the characterization of diesel fuels, and the repeatability of the data.     

Coupled LC-GC: The capacity of silica gel (HP)LC columns for retaining fat

Many applications of coupled LC-GC in food analysis require that LC separates large quantities of triglycerides from the components of interest. The capacities of silica gels to retain triglycerides have been determined for n-hexane as mobile phase as well as some eluent mixtures. Conclusions are drawn for practical applications.     

Determination of aflatoxins in olive oil by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometric with electrospray ionization (LC/ESI-MS/MS) method for determining the four naturally occurring aflatoxins (AFs) B1, B2, G1, and G2 in olive oil is proposed. AFs were extracted from oil sample by means of matrix solid phase dispersion (MSPDE), utilizing C18 as dispersing material. No further purification step, such as lipid removal, was performed. Aflatoxin M1, the hepatic metabolite of AFB1, was employed as internal standard. Olive oil extract was analyzed by LC/ESI-MS/MS in positive ionization mode, with multireaction monitoring acquisition. Due to a signal suppression ranging between 4 and 23%, quantitation was performed by matrix-matched calibration curves. The regression line coefficients of determination were above 0.9991. Sample recoveries ranged from 92 to 107%, with relative standard deviations below 13% for spiking levels between 0.5 and 5 ng g⁻¹; method quantification limits ranged between 0.04 and 0.12 ng g⁻¹. The developed LC/ESI-MS/MS method, although not as sensitive as LC coupled to fluorescence detection, is rapid, selective, accurate and precise, thus it can be used as confirmatory assay. The MSPDE appears suitable for application to other oleaginous matrices and for multiresidue investigation.     

Determination of betaines in vegetable oils by capillary electrophoresis tandem mass spectrometry--application to the detection of olive oil adulteration with seed oils

A CE–tandem mass spectrometry (MS²) methodology enabling the simultaneous determination of betaines (glycine betaine, trigonelline, proline betaine and total content of carnitines) in vegetable oils was developed. Betaines were derivatized with butanol previous to their baseline separation in 10 min using a 0.1 M formic acid buffer at pH 2.0. Ion trap conditions were optimized in order to maximize the selectivity and sensitivity. Analytical characteristics of the proposed method were established by evaluating its selectivity, linearity, precision (RSDs ranged from 4.8 to 10.7% for corrected peak areas) and accuracy by means of recovery studies (from 80 to 99%) and LODs and LOQs at 0.1 ppb level. The method was applied for the determination of the selected betaines in seed oils and extra virgin olive oils. MS² experiments provided the fingerprint fragmentation for the betaines identified in vegetable oils. In extra virgin olive oils, carnitines were not detected, making it possible to propose them as a feasible novel marker for the detection of adulterations of olive oils. Application of the developed method for the analysis of different mixtures of extra virgin olive oil with seed oil (between 2 and 10%) enabled the detection and quantitation of the total content of carnitines. The results obtained show the high potential of the developed method for the authentication and quality control of olive oils.     

Mixing in the sample loop of the loop-type interface in coupled LC-GC

During introduction of an LC fraction into the sample loop of the loop-type interface mixing occurs between the fraction of interest and the material previously eluted from the LC. Such mixing may not only result in losses of the solute material of interest, but also in contamination of the fraction of interest with material from which it was supposed to have been isolated. Experimental determination of the extent of mixing has led to the conclusion that whereas the effects are negligible under some conditions, in some circumstances the mixing can cause severe problems.     

New on-line concentrator for LC-GC: Analysis of PAHs with LC-GC

A new, versatile, and low cost on-line LC-GC interface has been devloped for the fast and reliable introduction of large volume samples into a cappillary GC column without using the conventional retention gap. PAHs in soot were analyzed by on-line normal phase HPLC-capillary GC. A glass, vial-shaped on-line concentrator provides a zone for solvent evaporation and sample concentration. Large volumes of HPLC eluate can be concentrated with the on-line concentrator and then transferred directly into the cappillary column. Trace levels (< 10 ppb) of PAH compounds can be efficiently concentrated with the on-line concentrator and determined without loss or contamination.     

Analysis of phytosterols in extra-virgin olive oil by nano-liquid chromatography

In this work the applicability of nano-liquid chromatography (nano-LC) was evaluated for the determination of phytosterols in extra-virgin olive oil samples. These compounds represent a minor part of lipids in vegetable oils, but their quantification can be useful to establish oil origin and to reveal intentional adulterations. The analysis of five main sterols, specifically brassicasterol, stigmasterol, campesterol, cholesterol and β-sitosterol, was performed in a laboratory-assembled nano-LC system coupled with a UV detector. The separation of all compounds was obtained in about 20 min, employing a capillary column packed with a C18-RP (sub-2 μm particles) stationary phase for 15 cm. Methanol only was used as mobile phase. The simple method developed and optimized was validated in terms of repeatability, linearity, limit of detection and limit of quantification (0.78 and 1.56 μg/mL, respectively) achieving good results. After this, it was applied to the determination of phytosterols in extra-virgin olive oil samples. Isolation of phytosterols was obtained by solid-phase extraction, after saponification and liquid–liquid extraction of the unsaponified fraction with diethyl ether. Recovery tests were performed and values between 90% and 103%, with RSDs within 5%, were obtained. Moreover the nano-LC system was coupled with a mass spectrometer for an accurate identification of phytosterols.     

顶空气相色谱-质谱测定橄榄调和油中橄榄油含量

建立了测定橄榄调和油中橄榄油含量的顶空气相色谱-质谱分析方法。对样品量、加热温度、加热时间、进样量、进样模式、色谱柱进行了优化。通过化学计量学方法发现了橄榄油的特征化合物。取1.0 g样品放置于20 m L顶空瓶中,在180℃加热振摇2 700 s,取1.0 m L顶空气体进样,通过HP-88色谱柱分离和质谱检测。结果表明,方法的线性范围为0~100%(橄榄油含量),线性相关系数(r2)大于0.995,检出限为1.26%~2.13%,模拟橄榄调和油中橄榄油含量测定的偏差为-0.65%~1.02%,相对偏差为-1.3%~6.8%,相对标准偏差为1.18%~4.26%(n=6)。该方法不使用任何溶剂,操作简单、快速、环保,灵敏度和准确度高,适用于橄榄调和油中橄榄油含量的测定。     

Determination of trace elements in olive oil by ICP-AES and ETA-AAS: A pilot study on the geographical characterization

The determination of trace elements in edible oils is important because of both the metabolic role of metals and possibilities for adulteration detection and oil characterization.The most commonly used techniques for the determination of metals in oil samples are inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectrometry (AAS). For this study, a microwave assisted decomposition of the olive oil in closed vessels using a mixture of nitric acid and hydrogen peroxide was applied as sample preparation.The low achievable LODs enable the determination by ICP-AES of even very low concentrations of most elements of interest. The proposed ICP-AES method permits the determination of Ca, Fe, Mg, Na, and Zn in olive oils. Elements present in small amounts (Al, Co, Cu, K, Mn, Ni) were measured by ETA-AAS in the same sample digest. The concentrations of Al, Co, Cu, K, Mn, and Ni were in the range from 0.15 to 1.5 μg/g and differ according to the geographical origin of the oils. For the amounts of Fe, Mg, Na, and Zn in the samples, no significant differences according to the geographical origin of the oils could be observed, the mean concentrations being 15.31, 3.26, 33.10, and 3.39 μg/g, respectively. The Ca content varies in the range of 1.3 to 9.0 μg/g.The dependency of the trace elemental content of olive oils on their geographical origin can be used for their local characterization.     

Determination of fenthion and fenthion-sulfoxide, in olive oil and in river water, by square-wave adsorptive-stripping voltammetry

Square-wave adsorptive-stripping voltammetry technique has been used to develop a method for the determination of fenthion in olive oil. Due to the fact that fenthion does not give any electrochemical signal at mercury electrode, the method has been based on a previous oxidation of fenthion to its metabolite, fenthion-sulfoxide, by using KMnO₄. The metabolite gives rise to a peak due to an adsorptive-reductive process at −0.786 V. Fenthion is isolated from olive oil by carrying out a solid–liquid extraction procedure using silica cartridge, followed by a liquid–liquid partitioning with acetonitrile. The detection limit in olive oil is 78.8 ng g⁻¹ and recoveries for four levels of fortification are ranged from 85% to 109%. On the other hand, it has been developed a method for the simultaneous determination of fenthion and its metabolite fenthion-sulfoxide, in river water. Pesticides are isolated from water by carrying out a liquid–liquid partitioning with trichloromethane. The detection limits are 0.41 ng g⁻¹ and 0.44 ng g⁻¹, for fenthion and fenthion-sulfoxide, respectively. Recoveries for three levels of fortification are ranged from 96% to 103% for fenthion and 94% to 104% for fenthion-sulfoxide.     

Isotope dilution determination of polycyclic aromatic hydrocarbons in olive pomace oil by gas chromatography-mass spectrometry

A gas chromatographic (GC) method with mass spectrometry detection (MS) for the determination of eight polycyclic aromatic hydrocarbons (PAHs) in olive pomace oil has been developed. The oil was diluted with n-pentane and extracted by liquid-liquid partition with dimethyl sulphoxide (DMSO). After water addition and back-extraction with cyclohexane, a thin-layer chromatography on silica gel was performed as a further purification step. The PAHs spot was scraped off from the plate and the final extract was concentrated and analysed by GC-MS in full scan mode. The eight PAHs under investigation were determined in the presence of the corresponding labelled compounds added as internal standards to the sample at the beginning of the analytical process. The identified PAHs were then quantified by the isotope dilution methodology assuring the compensation of the concentration of each analyte for any variation in the sample preparation. The method precision was satisfactory with relative standard deviation (R.S.D.) values in the range 3.6-12.7% for all PAHs. The average recovery rates ranged from 69.0 to 97.5%. Accuracy was also calculated for benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd]pyrene and benzo[ghi]perylene by analysing a certified reference material (CRM 458, coconut oil) with adequate results. All response curves exhibited a linear fit from 0.1 to 10 microg ml(-1) and the determination coefficients R2 were better than 0.9942. The limits of detection (0.1-0.4 microg kg(-1)) were acceptable when compared with the maximum permitted limit of 2 microg kg(-1) for each of the eight considered PAHs and 5 microg kg(-1) for the sum of the eight PAHs established by the Italian legislation. Measurement uncertainty was finally calculated identifying and quantifying the uncertainty components of the analytical process. The relative expanded uncertainties (Uc), expressed as percent values were in the range 8.5-11.4% thus appropriate for residues quantification in the range of concentrations considered in the present study.     

Microwave-assisted extraction at atmospheric pressure coupled to different clean-up methods for the determination of organophosphorus pesticides in olive and avocado oil

An effective extraction method was devised for the determination of organophosphorus pesticides (OPPs) in olive and avocado oil samples, using atmospheric pressure microwave-assisted liquid–liquid extraction (APMAE) and solid-phase extraction or low-temperature precipitation as clean-up step. A simple glass system equipped with an air-cooled condenser was designed as an extraction vessel. The pesticides were partitioned between acetonitrile and oil solution in hexane. Analytical determinations were carried out by gas chromatography-flame photometric detection and gas chromatography–tandem mass spectrometry, using a triple quadrupole mass analyzer, for confirmation purposes. Several factors influencing the extraction efficiency were investigated and optimized through fractional factorial design and Doehlert design. Under optimal conditions the recovery of pesticides from oil at 0.025 μg g⁻¹ ranged from 71% to 103%, except for fenthion in avocado oil, with RSDs ≤13% (n = 5). The LOQ for the entire method ranged from 0.004 to 0.015 μg g⁻¹. Finally, the proposed method was successfully applied to the extraction and determination of the selected pesticides in 20 commercially packed extra virgin olive oils and four commercially packed avocado oils produced in Chile. Detectable residues of different OPPs were observed in 85% of samples.     

Chemiluminescent evaluation of peroxide value in olive oil

A method is described for the evaluation of the peroxide value (PV, meq. O₂ kg⁻¹) in olive oil. The method is based on the chemiluminogenic energy-transfer reaction of bis(2,4,6-(trichlorophenyl)oxalate (TCPO) with hydrogen peroxide or total peroxides in the presence of Mn(II) as catalyst and 9,10-dimethylanthracene as fluorophore. The procedure developed allows the evaluation of PV within the range of 0.6-100 meq. O₂ kg⁻¹ (CL intensity = 1.76 × PV (meq. O₂ kg⁻¹) + 23.2, r² = 0.994, n = 9) and relative standard deviation within the range 1-5% by using a simple manual measurement.