Optimization of an analytical methodology for the determination of alkyl- and methoxy-phenolic compounds by HS-SPME in biomass smoke

A sampling and analysis method for the determination of 21 phenolic compounds in smoke samples from biomass combustion has been developed. The smoke is used to make smoked foods, following an artisanal procedure used in some parts of the Canary Islands. The sampling system consists of a Bravo H air sampler, two impingers, each one containing an aqueous solution of sodium hydroxide 0.1 mol L⁻¹, followed by a silica gel trap. The variables optimized to reach the best sampling conditions were volume of absorbent solution and sampling flow. Under the optimum conditions, 100 mL of absorbent solution of NaOH 0.10 mol L⁻¹ and 2 L min⁻¹ for the sampling flow, sampling efficiencies are higher than 80%. Analysis of phenolic compounds was carried out by headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography–mass spectrometry (GC-MS). Five different fiber coatings were employed in this study. By means of a central composite design, extraction time, salt concentration, and pH of the solution were optimized: 65-μm carbowax–divinylbenzene, extraction time 90 min, concentration in NaCl of 35% (m/v), and pH 2 yielded the highest response. Detection limits of phenol and their alkyl derivatives, guaiacol and eugenol, are between 1.13 and 4.60 ng mL⁻¹. 3-Methoxyphenol, 2,6-dimethoxyphenol, and vanillin have detection limits considerably higher. Good linearity (R ²≥0.98) was observed for all calibration curves in the established ranges. The reproducibility of the method (RSD, relative standard deviation) was found to oscillate between 7 and 18% (generally close or lower than 10%).     

混合食品中19种菊酯类农药残留的极性区间排列净化-气相色谱-质谱法测定

基于目标化合物的极性性质,提出了极性区间排列净化方法,设计实验条件使产生某一极性区间,采用边界调节优化手段达到目标化合物与其它干扰杂质分离的目的。以此为核心步骤,建立了固相萃取/气相色谱-质谱法检测饺子、包子、盘菜等混合食品中19种菊酯类农药残留的分析方法。样品用乙酸乙酯-乙腈(体积比1∶9)混合溶剂提取,Envi-18柱和Florisil柱净化后进行测试。采用选择离子扫描方式,外标法定量。该方法简便、快速,在优化实验条件下,烯丙菊酯、氟氯氰菊酯、氯氰菊酯的定量下限(S/N≥10)为0.02 mg/kg,其它16种菊酯的定量下限均小于0.01 mg/kg,在加标水平为0.01、0.02、0.1 mg/kg时,回收率为76%~128%,相对标准偏差为3.8%~14.7%。     

Activated aluminum oxide selectively retaining long chain n-alkanes: Part II. Integration into an on-line high performance liquid chromatography-liquid chromatography-gas chromatography-flame ionization detection method to remove plant paraffins for the determination of mineral paraffins in foods and environmental samples

Aluminum oxide activated by heating to 300-400 °C retains n-alkanes with more than about 20 carbon atoms, whereas iso-alkanes largely pass non-retained (with characteristics described in more detail in Part I). This property is useful for the analysis of mineral oil contamination of foods and other matrices: it enables the removal of plant n-alkanes, typically ranging from C₂₃ to C₃₃, when they disturb the analysis of mineral paraffins (usually almost exclusively consisting of iso-alkanes). An on-line HPLC-LC-GC-FID method is proposed in which a first silica gel HPLC column isolates the paraffins from the bulk of edible oils or extracts and is backflushed with dichloromethane. In a second separation step, a 10 cm × 2 mm i.d. column packed with activated aluminum oxide separates the long chain n-alkanes from the fraction of the iso-alkanes which is transferred to GC-FID by the on-column interface and the retention gap technique. The retained n-alkanes are removed by flushing with iso-octane.     

固相萃取-超高效液相色谱-串联质谱法同时测定保健食品中21种非法添加化合物

建立了固相萃取-超高效液相色谱-串联质谱同时测定保健食品中21种非法添加化合物的方法。样品用乙腈超声提取后，采用HLB固相萃取小柱净化，经Waters BEH C18色谱柱（100 mm×2.1 mm，1.7 μm）分离，以10 mmol/L乙酸铵和甲醇为流动相进行梯度洗脱，采用电喷雾电离（ESI）源，在多反应监测模式下检测。结果表明，21种非法添加化合物均呈良好的线性关系，相关系数均≥0.995，不同基质的检出限为3~160 μg/kg，回收率为61.8%~109.3%，相对标准偏差为1.6%~14.7%。该方法可用于减肥类、降脂类、降糖类、降压类保健食品中21种非法添加药物的同时测定。     

Interaction studies of vinychloride with liquid foods by gas chromatography

Summary The interaction of vinylchloride (VC) with liquid foods, such as water, olive oil and honey, was studied using the relatively new technique of Reversed-Flow Gas Chromatography (RFGC). The RFGC method permits the calculation of the VC diffusion coefficient in the liquid phase (water, oil and honey) and the determination of the partition coefficient of VC between the liquid and the carrier gas, as well as the determination of the Henry's constant of VC in the liquid food. From the variation of the above parameters with temperature, thermodynamic parameters (free and excess free energies, enthalpies, entropies and activity coefficients) were calculated for the adsorption of VC by liquid foods. These are discussed in comparison with the same parameters calculated from empirical equations or determined experimentally by other techniques.     

Crust density in bread baking: Mathematical modelling and numerical solutions

A model for the formation of a “crust” during bread baking is presented. The crust is the outermost part of the loaf where the final bread density is significantly higher than in the “crumb”, the interior of the loaf. The model is based on a collapse mechanism, whereby raised pressures due to thermal expansion and water evaporation squash bubbles in the bread as the dough sets and fractures; the latter process allows vapour within bubbles to escape.     

烘烤温度对溶胶-凝胶法制备镧掺杂钛酸铋薄膜结构与铁电性质的影响

采用溶胶-凝胶法，在保持薄膜结晶温度和有机物分解温度相同情况下，发现烘烤温度（即溶剂的挥发温度）对镧掺杂钛酸铋薄膜的晶体结构、表面形貌和铁电性质均产生重要影响.在较低烘烤温度下得到的薄膜（117）择优取向明显.但随着烘烤温度增加，薄膜的（117）择优取向逐渐减弱.薄膜的表面晶粒形貌则从棒状逐渐转变为盘状.还测量了薄膜的铁电性质，发现在250℃烘烤温度下得到的薄膜具有最大的剩余极化强度，2Pr为28.4μC/cm2.对实验现象进行了定性解释. 关键词： 溶胶-凝胶法 烘烤温度 铁电薄膜     

Activated aluminum oxide selectively retaining long chain n-alkanes. Part I, description of the retention properties

Aluminum oxide activated by heating to 350-400 °C retains n-alkanes with more than about 20 carbon atoms, whereas iso-alkanes largely pass the column non-retained. Retention of n-alkanes is strong with n-pentane or n-hexane as mobile phase, but weak or negligible with cyclohexane or iso-octane. It is strongly reduced with increasing column temperature. Even small amounts of polar components, such as modifiers or impurities in the mobile phase, cause the retention of n-alkanes to irreversibly collapse. Since n-alkanes are not more polar than iso-alkanes and long chain n-alkanes not more polar than those of shorter chains, retention by a mechanism based on steric properties is assumed. The sensitivity to deactivation by polar components indicates that polar components and n-alkanes are retained by the same sites. The capacity for retaining n-alkanes is low, with the effect that the retention of n-alkanes depends on the load with retained paraffins. These retention properties are useful for the pre-separation of hydrocarbons in the context of the analysis of mineral oil paraffins in foodstuffs and tissue, where plant n-alkanes, typically ranging from C₂₃ to C₃₃, may severely disturb the analysis (subject of Part II).     

柱后光化学衍生荧光检测高效液相色谱法测定食品中的维生素B1

研究柱后光化学衍生荧光检测谪效液相色谱分离测定食品中维生素Ｂ１的方法。采用Ｃ１８柱,以含有２％乙腈的ＰＨ４．０磷酸盐缓冲液（０．１ｍｏｌ／Ｌ）作流动相反相分离,猪肝等食品中的维生素Ｂ１可与其它杂质达到完全分离。色谱流出液在柱后与０．７５％ＮａＳＯ３－４％,ＮａＯｈ的混合试剂溶液在线汇合报流经一聚四氟乙烯（ＰＴＦＥ）细管制成的光化学反应器时,维生素了转化为强荧光产物,由荧光检测器测定。在最佳条件下,