Separation and determination of tocopherols in vegetable oils by solid phase extraction on porous polymers SPE cartridges and capillary gas chromatography analysis

In this study we present the solid phase extraction selectivity of tocopherols from vegetable oils using four porous polymers (Porapak P, Porapak Q, Porapak QS, Porapak N). The tocopherols elution from SPE cartridges was performed using several hexanes:ethyl acetate mixtures (100:0, 95:5, 90:10, 85:15, v/v). Tocopherols (α, γ and δ-tocopherol) were analyzed by gas chromatography without any derivation steep. The amount of NaOH used for triglyceride removal was optimized. Particularly liquid-liquid and solid phase extraction methods for the extraction of tocopherols from vegetable oils were compared. The results confirmed that porous polymers represent promising SPE alternatives for the extraction of tocopherols from oils.     

Determination of sterols, erythrodiol, uvaol and alkanols in olive oils using combined solid-phase extraction, high-performance liquid chromatographic and high-resolution gas chromatographic techniques.

A method is described for the determination of the sterol, erythrodiol, uvaol and alkanol content in olive oils by means of solid-phase extraction and high-performance liquid chromatography, instead of liquid-liquid and thin-layer chromatographic separations, the following step being high-resolution gas chromatographic separation. This type of procedure allows the simultaneous analysis of a larger number of samples and a substantial reduction in manual operations. Comparisons were made between the two methods on 100 different olive oils and with a statistical analysis of the results (Student's t-test).     

Quantification of free and esterified sterols in Portuguese olive oils by solid-phase extraction and gas chromatography-mass spectrometry

A simple and accurate method based on solid-phase extraction (SPE), transesterification and gas chromatography-mass spectrometry (GC-MS) was developed for the quantitative analysis of free and esterified sterols of olive oil. In order to achieve better separation of esterified and free sterols, silica and alumina SPE adsorbents were tested. Separations by silica provided more reproducible results. The transesterification of both sterol fractions was found to be more user friendly than saponification as a method to liberate the sterols from the respective esters. The free sterols were then silylated with N,O-bis-trimethylsilyltrifluoroacetamide (BSTFA) with 1% of trimethylchlorosilane (TMCS). The most favourable conditions for exploitation of this reagent were established. The optimized methodology was suitable for evaluation of free and esterified sterols in Protected Designation of Origin (PDO) olive oils and monovarietal olive oils with different maturation indices. The prevailing phytosterols in all olive oils were beta-sitosterol and campesterol. The free sterols predominated, although they seemed to decrease with the maturation of the olive fruits.     

Chromatographic analysis of plant sterols in foods and vegetable oils.

This paper reviews recently published chromatographic methods for the analysis of plant sterols in various sample matrices with emphasis on vegetable oils. An overview of structural complexities and biological/nutritional aspects including hypocholesterolemic activities of phytosterols is provided in the Section 1. The principal themes of the review highlight the development and application of chromatographic techniques for the isolation, purification, separation and detection of the title compounds. Pertinent gas chromatographic and high-performance liquid chromatographic methods from the literature are tabulated to illustrate common trends and methodological variability. The review also covers specific analyses of natural/synthetic standard mixtures to shed light on potential applicability in plant sample assays. Examples of combined chromatographic techniques linked in tandem for the analysis of complex samples are included. Elution characteristics of sterol components are discussed in the context of analyte substituent effects, structural factors and stationary/mobile phase considerations.     

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.     

Analysis of sterols in vegetable oils using off-line SFC/capillary GC-MS

Summary The analysis of sterols in vegetable oils by off-line SFC followed by capillary GC-MS is described. The fractionation of the sterols from the complex oil matrix is achieved by SFC on aminopropyl silicagel in less than 8 minutes. Injection and collection of the sterol fraction is fully automated and time controlled. The sterols are analysed without derivatisation by capillary GC-MS. Identification is performed by full scan electron ionisation and quantitation is carried out by extracted ion chromatography at m/e 107, with cholesterol as internal standard. The analyses of the sterols from the sunflower oil and two olive oils illustrate the possibilities of the method.     

Liquid chromatographic determination of tocopherols and tocotrienols in vegetable oils, formulated preparations, and biscuits

A precise and selective liquid chromatographic procedure for determining tocopherol and tocotrienol isomers in vegetable oils, formulated preparations, and biscuits was developed and validated. The proposed method quantitates vitamin E in better conditions of recoverability and reproducibility than the standard saponification procedure. Tocopherols and tocotrienols were extracted in hexane from vegetable oils, passed through a silica Sep-pak, chromatographed on a mu-Bondapak C18 column with a mobile phase of methanol-water (95 + 5, v/v), identified at 292 nm, and detected with fluorescence procedure (excitation 296 nm, and emission 330 nm). The correlation coefficient on the calibration curve was 0.9995 over the range of 0.1 to 100 microg/mL. Overall recovery of vitamin E isomers was 93%; coefficients of variation for intra- and interday precision, < 2.25%. The results obtained from extraction methods 1 (with saponification) and 2 (without saponification) were compared by ANOVA test. Significant differences appeared between vitamin E isomers (p < or = 0.05).     

固相萃取-毛细管气相色谱法测定枇杷花中有机氯农药残留量

建立了枇杷花中有机氯类农药残留量的固相萃取-毛细管气相色谱(SPE-CGC)分析方法。对采自福建蒲田等12地的枇杷花中六六六(4种异构体)、滴滴涕(4种异构体)、五氯硝基苯共9种有机氯农药的残留量进行了测定。样品采用丙酮超声波提取,浓缩后过Florisil固相萃取小柱净化,洗脱剂为V(正己烷)∶V(丙酮)100∶1。用DB-1701弹性石英毛细管气相色谱柱分离样品,微电子捕获检测器进行检测。9种有机氯农药的峰面积与其质量浓度均有良好的线性关系,相关系数均大于0.999,最低检测限为0.016~0.125μg/L,样品的加标回收率为85.4%~106.9%,相对标准偏差为1.8%~9.8%。该方法能够满足农药残留检测的要求。     

固相萃取-毛细管气相色谱法测定中草药及其土壤中多种有机氯农药残留量

建立了中草药及其土壤中多种有机氯农药残留量的固相萃取-毛细管气相色谱(SPE-CGC)分析方法,并对7种中草药及其土壤中多种有机氯农药残留量的相关性进行了初步研究。样品以正己烷-丙酮用超声波提取,Florisil(1 g)固相萃取小柱快速净化提取物。采用SPB-5弹性石英毛细管柱分离样品,GC-ECD检测7种中草药及其土壤中的13种有机氯农药的残留量。方法的线性范围为1.26×10-10~2.24×10-7g/mL;检出限为6.4×10-11~6.1×10-10g/mL;加样平均回收率为87.3%~104.4%(RSD为1.1%~7.0%)。     

Multiresidue analysis of pesticides in fruits and vegetables using solid-phase extraction and gas chromatographic methods

A new extraction and cleanup procedure with gas chromatography was developed for the sensitive determination of acephate, dimethoate, malathion, diazinon, quinalphos, chlorpyrifos, profenofos, alpha-endosulfan, beta-endosulfan, chlorothalonil and carbaryl using 1-chloro-4-fluorobenzene as an internal standard in fruits and vegetables. Several extracting and eluting solvents for solid-phase extraction were investigated. The overall extracting solvent with a mixture of acetone:ethyl acetate:hexane (10:80:10, v/v/v) and a eluting solvent of 5% acetone in hexane used with the RPC18 cartridge gave the best recovery for all of the investigated pesticides, and minimized the interference from co-extractants. Under the optimal extraction and clean-up conditions, recoveries of 85 - 99% with RSD < 5.0% (n = 3) for most of the pesticides at the 0.02 - 0.5 mg/kg level were obtained. The limit of detection was between 0.005 - 0.01 mg/kg and the limit of quantification was 0.01 mg/kg. This analytical procedure was characterized with high accuracy and acceptable sensitivity to meet requirements for monitoring pesticides in crops.     

Determination of nifedipine in plasma by a rapid capillary gas chromatographic method.

A rapid, specific and reliable gas chromatographic assay procedure for Nifedipine in plasma has been developed. With a single-step solvent extraction, and electron capture detection, the method is sensitive to 0.5 ng/mL of plasma and the standard curve is linear from 0.5 to 500 ng/mL. Samples are protected from light to prevent formation of photodecomposition products. The method has been used to monitor drug concentrations in patients receiving therapeutic doses.     

Multi-component analysis (sterols, tocopherols and triterpenic dialcohols) of the unsaponifiable fraction of vegetable oils by liquid chromatography-atmospheric pressure chemical ionization-ion trap mass spectrometry

A simple and sensitive method for the analysis of sterols, tocopherols and triterpenic dialcohols from the unsaponifiable fraction from oil samples in a single analytical run using liquid chromatography coupled to mass spectrometry was developed. With this method, the compounds could be detected directly after dissolving the unsaponifiable fraction in acetonitrile without necessity of time-consuming sample pre-treatment or derivatization. Separation of the analytes was carried out at room temperature, by using a C18 column (5 μm i.d. 3.0 mm × 250 mm) with a linear gradient of acetonitrile/water (0.01% acetic acid) at a flow rate of 1.5 mL/min. The full scan mass spectra of the investigated compounds were measured by an ion trap mass spectrometer equipped with an APCI ion source. The optimized methodology was suitable for the identification of 23 compounds belonging to different families present in olive oil and other kinds of oils, as well as for the quantification of 15 analytes (vs. their commercial standards).     

Determination of sulfonylurea herbicides in soil extracts by solid-phase extraction and capillary zone electrophoresis

Summary Sulfonylurea herbicides in soil extracts were concentrated using off-line solid-phase extraction (SPE), and determined by capillary zone electrophoresis (CZE) and UV detection. The method involves extraction of soils with 0.1 M NaHCO₃ solution and subsequent preconcentration by using C₁₈ cartridges prior to separation of the pesticide using CZE. The results show that a C₁₈ cartridge is suitable for the purification of sulfonylurea herbicides in soil extracts with the recoveries ranging from 65–103%. The separation conditions affecting the resolution and detection sensitivity was systematically investigated. The sulfonylureas were resolved well using 30 mM sodium acetate (NaAc)/acetic acid (HAc)+10% acetonitrile (ACN) buffer at pH 4.80. The calibration plots for the test solutes in the concentration of 0.2–50 mg L⁻¹ were linear with detection limits in the range of 0.05–0.10 mgL⁻¹. The proposed method has been successfully demonstrated for the determination of sulfonylurea herbicides in soil samples.     

Formation of pentafluorophenyldimethylsilylethers and their use in the gas chromatographic analysis of sterols.

The pentafluorophenyldimethylsilyl group is an excellent protecting group for steroid alcohols, giving volatile ethers, detectable at picogram levels in gas chromatography with an electron capture detector. By the use of five reagents, increasingly hindered hydroxyl groups can be protected, so that structural information about unidentified sterols can be obtained. Quantitative derivative formation for a wide range of hydroxyl groups is possible by selection of the correct reagent combination, without affecting unprotected enolizable ketones.     

Determination of melamine residue in liquid milk by capillary electrophoresis with solid-phase extraction

A novel solid-phase extraction-capillary electrophoresis (SPE-CE) method was developed for the determination of melamine residue in liquid milk. The conditions of SPE and CE were investigated and optimized. A 1% trichloroacetic acid plus 2.2% lead acetate solution were used for the extraction of analyte and the removal of protein. A Cleanert PCX SPE cartridges column was used for clean up. The 50 mM sodium dihydrogenphosphate running buffer (pH adjusted to 3.2 with citric acid) was used as a running buffer. The linearity is satisfactory in the range of 0.8-100 μg/mL with a correlation coefficient of 0.9998. Under the optimal conditions, the method limit of detection (LOD) and method limit of quantification were 0.12 mg/kg and 0.37 mg/kg, respectively. The recovery of melamine from different liquid milk samples was in the range of 89.5-98.5% with a relative standard deviation of 1.8-3.5%. The intra- and inter-day assay precision was 2.8% (n = 6) and 4.1% for five days, respectively. The developed method has been applied successfully for the determination of melamine residue in liquid milk samples. The results obtained by the proposed method agree with those obtained by high-performance liquid chromatographic method. The proposed method enables the quantitative determination of melamine residues at levels as low as 0.37 mg/kg in different liquid milk.     

Determination of free fatty acids in milk and cheese procedures for extraction,clean up,and capillary gas chromatographic analysis

A rapid, reliable and precise capillary gas chromatographic method for routine quantification of short- and long-chain free fatty acids (FFA) in milk and cheese is described. Procedures of (1) lipid extraction, (2) isolation of the FFA from milk and cheese extracts, and (3) capillary gas chromatographic analysis were developed and optimized. FFA can be extracted from cheese for 95–100% with ether-heptane after grinding with sodium sulfate and addition of 2.5 M sulfuric acid. From milk, 95–100 % of the FFA (≤ C8:0) are also extracted with ether-heptane after addition of ethanol and 2.5 M sulfuric acid. Internal standards are used to compensate for the losses of lower FFA (C2:0–C8:0) in the aqueous phase. In view of the excellent recovery (98–100 %) and a considerable saving of time, the use of an aminopropyl column is preferred for the isolation of the FFA from lipid-extracts. The underivatized FFA are separated directly by capillary gas chromatography making use of columns which enable accurate and rapid (≤ 40 min) determination of FFA C2:0–C20:0. With the method described, all major FFA (C2:0–C18:3) in milk and cheese can be quantified with good repeatability (rsd less then 2 %). The method is also applicable to the analysis of short-chain fatty acids in other products.     

Determination of volatile compounds in grape distillates by solid-phase extraction and gas chromatography

Solid-phase extraction (SPE) procedure on octadecylsilica (C18) was developed for accumulation of volatile compounds from grape distillates. The procedure was optimised for final analysis by capillary gas chromatography. At mass concentrations in model solutions ranging from 0.1 to 50 mg/l solid-phase extraction recoveries of all analytes ranged from 69% for 2-phenylethanol to 102% for capric acid, with RSD values from 2 to 9%. SPE recoveries of internal standards to be added in the sample solution prior to extraction, higher alcohols 2-ethyl-1-hexanol and 1-undecanol, were 97 and 93%, respectively, with RSD values of 3%. Detection limits of analyzed compounds in model solutions ranged from 0.011 mg/l for isoamyl acetate to 0.037 mg/l for caproic acid. Method efficiency was tested in relation to acetic acid content, volume fraction of ethanol and possible matrix effects. A significant influence of matrix on SPE efficiency for geraniol, cis-2-hexen-1-ol and cis-3-hexen-1-ol was detected. For the same reason, 2-phenylethanol could not be determined by developed SPE method in samples of grape distillates. The developed solid-phase extraction method was successfully applied to determine the differences in volatile compound content in different grape distillates produced by the distillation of crushed, pressed and fermented grapes.     

Determination of polycyclic aromatic hydrocarbons in vegetable oils using solid-phase microextraction-comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry

A simple and fast solid-phase microextraction method coupled with comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry was developed for analysis of polycyclic aromatic hydrocarbons in edible oil, performed directly in a hexane solution of the oil. Sampling conditions (solvent used, extraction time, extraction temperature and fiber rinsing time) were optimized by using a sample of oil fortified with a standard solution of polycyclic aromatic hydrocarbons. The method was validated by calculating linear range, correlation coefficient, accuracy, repeatability, detection limit and quantification limit. The method was applied to several oils collected from the market and directly from an olive pomace extraction plant.