Capillary headspace - gas chromatography for the characterization of the flavour of fresh vegetables

Summary Static headspace sampling combined with gas chromatography using open-tubular (capillary) columns for the characterization of the flavour of raw vegetables and some vegetable products is described. In order to avoid alteration of the composition of the volatiles, the sample was thermostated for a short time only. Although equilibrium between vapour and sample was not established the reproducibility of such conditions is demonstrated. Typical chromatograms are given; the most characteristic compounds present were identified by mass spectrometry. Enlarged text of a poster presented at the Twelfth International symposium on Capillary Chromatography, September 11–14, 1990, Kobe, Japan     

Validation and uncertainty assessment of rapid extraction and clean-up methods for the determination of 16 organochlorine pesticide residues in vegetables

Rapid and practical extraction methods were developed using dichloromethane and ethyl acetate for the routine determination of 16 organochlorine pesticide residues and applied to approximately 30 fresh vegetables (tomato, cucumber and pepper) by using GC-ECD. The procedures were validated. Measurement uncertainties were calculated by applying bottom-up approach. The average recoveries obtained for each pesticide ranged between 65 and 102% at three fortification levels. The uncertainties of the analytical methods were lower than 21 and 16% with and without recovery correction, respectively. The calculated limits of detection and quantification were typically less than 1 ng g⁻¹ that were much lower than the maximum residue levels.     

Gemüse,eine Quelle von Spurenbestandteilen für biologische Flüssigkeiten

Summary Most vegetables contain different amounts of iso- and anteiso-fatty acids, -methylated acids were detected too, but so far only in tomatoes. Vegetables contain a great variaty of hydroxylated acids, especially -hydroxy acids. The detected iso- and anteiso-fatty acids and alcohols may be the source of similar branched chain acids identified earlier in rather high amounts in skin and hairs of man and animals. They might also be the source of branched aldehyde components in plasmologens.

     

果蔬,饮料中抗坏血酸的新亚铜灵光度分析法

新亚铜灵光度法测定抗坏血酸具有灵敏、快速的特点。抗坏血酸的浓度在2～20 mg/L范围内与吸光度呈良好的线性关系。用于猕猴桃、西红柿、刺梨汁等样品的分析,其相对标准偏差在0.6～1.2%,测定各种样品抗坏血酸的含量与靛酚滴定法比较,获得一致的结果。     

壳聚糖修饰电极上的铁氰根离子对抗坏血酸的电催化氧化作用

在玻碳电极表面滴涂一层壳聚糖膜 ,壳聚糖分子中 -NH2 在酸性溶液中发生质子化 ,靠静电引力作用吸附富集荷负电的电子介体Fe(CN) 63 -,使其固定在电极表面 ,研究了此Fe(CN) 63 - 壳聚糖 GC修饰电极对抗坏血酸的催化氧化作用。抗坏血酸的浓度在 3.0× 1 0 -6～ 5 .0× 1 0 -3 mol L范围内呈很好的线性关系 ,相关系数为 0 .998,检测限达 1 .0× 1 0 -6mol L。该法已用于测定蔬菜中抗坏血酸的含量。     

Application of liquid chromatography with electrospray tandem mass spectrometry to the determination of a new generation of pesticides in processed fruits and vegetables

This paper describes a method for the sensitive and selective determination of 24 new pesticide residues (azoxystrobin, trifloxystrobin, kresoxim-methyl, fenazaquin, indoxacarb, fenothiocarb, furathiocarb, benfuracarb, imidachloprid, dimethomorph, fenpyroximate, hexythiazox, tebufenpyrad, tebufenozide, difeconazole, fenbuconazole, flusilazole, paclobutrazol, tebuconazole, tetraconazole, bromuconazole, etofenprox, fenhexamid, pyridaben) in apple puree, concentrated lemon juice and tomato puree. A miniaturized extraction-partition procedure requiring small amounts of non-chlorinated solvents was used. The extracts are analyzed by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS-MS) without any further clean-up step. The pesticides are separated on a reversed-phase polar column using a gradient elution. Fifty-five simultaneous MS-MS transitions of precursor ions were monitored (two or three for each pesticide). Studies at fortification levels of 0.001-0.020 and 0.010-0.200 mg/kg gave mean recoveries ranging from 76 to 106% for all compounds, except for imidacloprid, with (R.S.D.s) < or = 15%. The excellent sensitivity and selectivity of LC-MS-MS method allowed quantitation and identification at low levels also in difficult matrices with a run time of 20 min. With the developed method almost 100 samples of commercial fruit products (nectars, juices, purees) were analyzed. None of samples contained residues higher than 0.010 mg/kg.     

喷洒植物营养素后稻米、蔬菜、水果中几种微量元素的测定

对施用新型“农药”——植物营养素后几种不同农作物的前处理方法进行了研究,提出了操怍简便、精密、准确的测定方法,为在我国建立评价施药后农作物中微量元素变化水平提供了可靠的测试手段。并通过对施药前后,农作物中锌、铜、铁三种微量元素含量的测定和比较,为植物营养素类“农药”的卫生鉴定提供了新的指标。     

微波消解-石墨炉原子吸收光谱法和原子荧光光谱法测定蔬菜中痕量元素

用微波消解对蔬菜进行前处理，石墨炉原子吸收光谱法和原子荧光光谱法测定蔬菜中铅、镉、砷、汞的含量。用两种国家标准参考样品进行考察，结果表明该方法不仅简便、快捷而且分析结果可靠。并提出了该方法在蔬菜痕量元素测定中应注意的问题。     

Identification of polycyclic aromatic hydrocarbons and methoxylated phenols in wood smoke emitted during production of charcoal

Summary A method for detection, quantification, and confirmation of 30 multi-class pesticide residues in fresh vegetables by gas chromatography-tandem mass spectrometry (GC-MS-MS) has been developed. The optimum ionization mode, electron impact (El-MS-MS) or chemical ionization (Cl-MS-MS), was used for different groups of pesticides in a single run. The residues were previously extracted from vegetables with dichloromethane. A 10μL aliquot of the extract can be injected in routine analysis without a clean up step when the glass liner is used with Carbofrit. Recovery efficiencies ranged 70–119% at the two different fortification levels studied and the relative standard deviation was <16.9% for all compounds. The limit of detection of each compound was 30 ng Kg⁻¹−6 μg Kg⁻¹. The proposed method was applied to the routine analysis of pesticides in vegetables grown in an important greenhouses area located in El Ejido (Almería, Spain).     

Three-step extraction procedure for determination of heavy metals availability to vegetables

A three-step sequential extraction procedure was used to determine the concentration of heavy metal speciation forms in soil. The procedure allows one to identify the pool of heavy metals that can be potentially mobilised under changes in soil pH value or redox potential. It has been shown that similar portions of heavy metals are present in reducible, oxidisable and residual fractions. It was found that soil chemical properties significantly affected the distribution of heavy metals among different fractions and their uptake by vegetables. Cadmium was a dominant element which occurred in the exchangeable fraction—the most bioavailable and potentially toxic.