Determination of phenolic antioxidants by micellar electrokinetic capillary chromatography with electrochemical detection

A new and efficient method for the determination of synthetic phenolic antioxidants (SPAs) has been developed by using micellar electrokinetic capillary chromatography (MECC) with electrochemical detection. Under the optimum conditions, all analytes were successfully separated within 13 min at the separation voltage of 18 kV in a 20 mmol/L borate running buffer (pH 7.4) containing 25 mmol/L sodium dodecyl sulfate. The excellent linearity was obtained in the concentration range from 5.0 × 10⁻⁴ to 2.0 × 10⁻⁶ mol/L and the detection limits (S/N = 3) of propyl gallate (PG), tert-butylhydroquinone (TBHQ), butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT) range from 2.9 × 10⁻⁷ to 2.7 × 10⁻⁶ mol/L. This method has been proved to be effective and successfully applied for the determination of SPA in food products, providing a promising and convenient entry to monitor the superscale use of phenolic antioxidants.     

Optimal conditions for determination of zinc bacitracin, polymyxin B, oxytetracycline and sulfacetamide in animal feed by micellar electrokinetic capillary chromatography

A separation technique for zinc bacitracin, polymyxin B, oxytetracycline and sulfacetamide in animal feedstuffs by micellar electrokinetic capillary chromatography (MEKC) was developed. The running buffer was 20 mmol l^-1 borate, 20 mmol l^-1 phosphate, pH 8.4, containing 20 mmol l^-1 sodium dodecylsulphate and 10% (v/v) methanol. MEKC was performed at 25°C; the applied voltage was 25 kV with a running pressure of 10 mbar. Simultaneous UV detection for all analytes was at 215 nm. The method was validated for specificity, accuracy, linearity, precision and robustness. It was shown to be specific, accurate (recoveries were 99.7 ± 0.3, 99.9 ± 0.9, 99.8 ± 1.0 and 99.5 ± 0.4, respectively, for oxytetracycline-, sulfacetamide-, polymyxin B- and zinc bacitracin-spiked samples of feed for cow, pigs, chicken and cattle), linear over the tested range (correlation coefficients ≥0.9987) and precise (RSDs below 1.8% for each analyte). The method was applied to determine zinc bacitracin, polymyxin B, oxytetracycline and sulfacetamide as additives in animal feed.     

Simultaneous determination of lovastatin and citrinin in red yeast rice supplements by micellar electrokinetic capillary chromatography

Lovastatin is a main component of Monascus purpureus fermented red rice contributing to the lipid-lowering effect. Citrinin is a toxic fermentation by-product which can be found as a contaminant. An accurate, simple and rapid micellar electrokinetic capillary chromatographic method was developed for the first time for simultaneous determination of lovastatin present in lactone and hydroxy acid forms and citrinin in red rice products provided by different manufacturers and formulated in various dosage forms. Separation was achieved within only 2 min using 20 mM of phosphate buffer at pH 7.0 and 30 mM of sodium dodecyl sulphate at an applied voltage of 25 kV. Sensitivity crucial for detecting citrinin was enhanced by using an extended light path capillary. The results showed that the content of lovastatin and its acid form in dietary supplements were considerably different indicating the need for improved standardization in order to ensure efficiency and safety of these products.     

Determination of potentially anti-carcinogenic flavonoids in wines by micellar electrokinetic chromatography

A micellar electrokinetic chromatography (MEKC) is developed for the determination of potentially anti-carcinogenic flavonoids in various types of wines. The factors affecting the separation and detection, including the concentration and pH of the running buffer, the injection time, the sodium dodecyl sulphate (SDS) concentration, and the wavelength of UV absorption monitored were investigated to find the optimum conditions. Six potentially anti-carcinogenic flavonoids were separated within 16 min in a borate buffer containing SDS at pH 9.0. The detection limits for the six analytes were in the range of 1.48 × 10⁻² − 2.31 × 10⁻² μg mL⁻¹. The method was successfully used in the analysis of wines with a relatively simple extraction procedure.     

Method development for sensitive determination of nisin in food products by micellar electrokinetic chromatography

A rapid and sensitive micellar electrokinetic chromatography (MEKC) method has been developed for the identification and quantification of nisin in food products. Factors such as micelle concentration, pH, and concentration of the buffer were investigated in order to determine the optimum conditions for the analysis. Using optimised conditions of a background electrolyte containing 50 mM sodium phosphate, 80 mM sodium dodecyl sulphate (SDS) at pH 3.75 enabled the successful detection of nisin within 6 min. Limits of detection (LOD) and quantification (LOQ) were in the range of 0.3–0.8 and 1.0–2.8 mg L⁻¹, respectively. The calibration curves were linear for nisin concentration over the range of 2–60 mg L⁻¹. The relative standard deviation (RSD) of the peak area ratios and migration times for method repeatability (n = 3) were found to be lower than 5% and 1%, respectively. The potential of the proposed method to be used for quantitative determination of nisin concentrations in food materials was demonstrated by spiking food samples including dairy products, salad dressings, alcoholic beverages and canned tomatoes with known concentrations of nisin. Quantitative recoveries ranging from 83% to 104% were obtained in the food matrices.     

Determination of phenolic acids in coffee by micellar electrokinetic chromatography

A seven-minute micellar electrokinetic chromatography analytical procedure capable of resolving the five principal phenolic acids in coffee, including the isomers of 5-caffeoylquinic acid (5-CQA), 4-CQA and 3-CQA, caffeic acid and ferulic acid is reported. The electrophoretic conditions consisted of an SDS (70 mM)-phosphate (17.6 mM)-methanol (5% v/v) buffer system, pH 2.5, 22.1 °C, −17 kV and detection at 325 nm. The Joule effect and the possible interactions between the buffer components and temperature with respect to peak quality, resolution and selectivity were assessed in the concentration range of 25–900 μg/mL. Performance evaluation of the system used a 3^3–7 factorial design at the 95% confidence level. The lowest correlation coefficient for linearity was 0.99888 for the 4-CQA. Limits of detection and quantification were 0.98 and 4 μg/mL. The method was tested with both green and roasted coffee beans using four systems of extraction.     

Solid-phase microextraction and sample stacking micellar electrokinetic chromatography for the analysis of pesticide residues in red wines

Solid-phase microextraction (SPME) in combination with sample stacking micellar electrokinetic chromatography (MEKC) was studied for the simultaneous determination of 11 multi-class pesticides residues (pirimicarb, metalaxyl, pyrimethanil, procymidone, nuarimol, azoxystrobin, tebufenozide, fenarimol, benalaxyl, penconazole and tetradifon) in red wines samples. Pesticide residues present in the samples were preconcentrated by SPME using poly(dimethylsiloxane)/divinylbenzene (PDMS/DVB) fibers and the injection of large sample volumes into the capillary by reversed-electrode polarity stacking mode (REPSM). Validation of the method was carried out. The combination of both preconcentration procedures (SPME and REPSM) allowed the determination of 10 of these pesticides in red wines at concentrations between 0.049 and 1.69 mg/L (i.e., levels well below the maximum residue limits (MRLs) allowed for these compounds in wine grapes, except for pirimicarb). Repeatability and accuracy of the SPME-MEKC-DAD method was verified by five consecutive extractions of spiked red wine samples at three levels of concentration. Apparent recovery values were in the range 90–107%. The potential of the method was demonstrated by analyzing multiple homemade red wine samples from the Canary Islands and two commercial samples. Only pyrimethanil, procymidone and azoxystrobin were found in the homemade samples; among them, the pesticide most frequently detected was procymidone.     

Air classification of barley flours to produce phenolic enriched ingredients: Comparative study among MEKC-UV, RP-HPLC-DAD-MS and spectrophotometric determinations

The aim of this paper was to use the air classification technology to produce barley flours enriched in phenolic compounds and to obtain naturally enriched ingredients for pasta and bakery industry.Phenolic compounds in barley have been described in literature using different methodologies that are not easily comparable. This paper describes a comparative study between different separative and spectrophotometric methods to determine free and bound phenolic compounds in barley flours and their air classified fractions from three different cultivars grown in the same experimental field.To this end, reversed phase-high performance liquid chromatography, micellar electrokinetic chromatography, and spectrophotometric determinations were applied.The barley phenolic compounds analyzed included mainly catechins and proanthocyanidins as free phenols, and hydroxycinnamic acids and their derivatives as bound phenols.The enriched fractions obtained by air classification showed an increase of free flavan-3-ols of 157-173% compared to whole flour. The same fractions also reported larger concentration of bound phenolic compounds (160-236%) with respect to whole flours. Air classification results a good technique to enrich the flours and to utilize the barley co-products.     

毛细管气相色谱法测定食品中的酚类抗氧化剂

建立了同时测定食品中BHA、BHr、TBHQ和PG等四种酚类抗氧化剂的测定方法.采用HP-1毛细管色谱柱分离,氢火焰离子化检测器外标法定量,样品加标回收率为96.3%～104.2%,相对标准偏差为0.63%～1.53%,检出限分别为BHA为0.72mg/L、BHT为0.62mg/L、TB-HQ为0.68mg/L、PG为1.2mg/L.该方法具有快速、灵敏度高、重现性好、预处理简单等优点.     

毛细管气相色谱法测定糕点中丙酸含量

建立了糕点中丙酸含量的毛细管气相色谱测定方法。采用WBI进样口,毛细管色谱柱J＆WDB1701（中等极性30m×0．53mm×1μm）,FID检测器进行检测。进样口温度：200℃,载气流速：6mL／min,柱室温度：40℃保持3min,以3℃／min升至200℃,检测器温度：250℃,样品用硫酸溶液酸化无水乙醇定容后直接进样测定。方法简单、快速、重现性好,平均回收率大于90％,RSD小于3．0％,线性范围为10μg／mL～200μg／mL。     

Analysis of volatile compounds in edible oils using simultaneous distillation-solvent extraction and direct coupling of liquid chromatography with gas chromatography

 Identification of volatile compounds in different edible oils (i.e. olive oil, almond oil, hazelnut oil, peanut oil and walnut oil) was performed using simultaneous distillation-solvent extraction followed by gas chromatographic-mass spectrometric analysis. An alternative approach which allows the direct injection of the oil sample (i.e. without any kind of pre-treatment) and involves the use of on-line coupled reversed phase liquid chromatography-gas chromatography (RPLC-GC) was also considered and the advantages of avoiding off-line preseparation for the analysis of volatile compounds were underlined regarding difficulties associated with the lipophilic nature of most volatile compounds and, hence, with the reliability of their analysis. Received: 14 June 1999 / Revised version: 3 August 1999     

Determination of synthetic phenolic antioxidants in soft drinks by stir-bar sorptive extraction coupled to gas chromatography-mass spectrometry

The synthetic phenolic antioxidants butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tert-butyl hydroquinone (TBHQ) were pre-concentrated by stir-bar sorptive extraction and thermally desorbed (SBSE-TD) before analysis by GC-MS. Several parameters affecting the derivatisation step and both SBSE extraction and thermal desorption were carefully optimised. When the analyses of BHA and TBHQ in their acetylated, silylated and underivatised forms were compared, the best results were obtained when the in-situ derivatisation procedure with acetic anhydride was employed. Quantification was carried out using carvacrol as the internal standard, providing quantification limits of between 0.11 and 0.15 ng ml^?1, depending on the compound. Recovery assays for samples spiked at two concentration levels, 1 and 5 ng ml^?1, provided recoveries in the 81–117% range. The proposed method was applied in the analysis canned soft drinks and the analytes were found in five of the 10 samples analysed.     

Direct determination of phenolic compounds and phospholipids in virgin olive oil by micellar liquid chromatography

A simple HPLC method is reported for fast separation and determination of phenolic compounds (tyrosol, caffeic acid, p-coumaric acid and oleuropeina) and phospholipids (phosphatidylethanolamine and phosphatidylcholine) in virgin olive oil samples. The samples were diluted with 2-propanol and injected into the column directly without previous extraction. Samples with an olive oil content of up to 65% were injected without any problems. The analytes were separated on a C-18 column by a micellar mobile phase containing 0.07 M SDS and 2.5% 2-propanol at pH 3, and were detected at 210 nm. Linear calibration curves [r² > 0.997] were obtained with detection limits ranging from 0.052 to 0.16 μg/g and 1 to 8.6% repeatability for the phenolic compounds. Several virgin olive oil samples were analysed and the recovery values were around 110%.     

毛细管柱气相色谱法测定食品中微量甜蜜素

研究了测定食品中微量甜蜜素的毛细管柱气相色谱ECD分析方法。结果显示,该法的线性范围是0．01～10．0μg／mL,最低检出限为0.05μg／g,回收率为93.0％～104．0％。     

Analysis of synthetic antioxidants and preservatives in edible vegetable oil by HPLC/TOF-MS

The application of high performance liquid chromatography time-of-flight mass spectrometry (HPLC/TOF-MS) for the qualitation and quantitation of 11 synthetic antioxidants and preservatives in edible vegetable oil samples is reported here. The qualitation by HPLC/TOF-MS is accomplished with the accurate mass of the deprotonated molecules [M−H]⁻, along with the accurate mass of their main fragment ion. In order to obtain sufficient sensitivity for quantitation purposes (using deprotonated molecule), segment programme of fragmentor voltage is designed in negative ion mode. The mass accuracy typically obtained is routinely better than 5 ppm. The 11 compounds behave linearly in the 0.05–5.0 mg/kg concentration range, with correlation coefficient >0.997. The recoveries at the tested concentrations of 0.1–2.0 mg/kg are 65.8–106.9%, with coefficients of variation <8.1%. The method illustrated is suitable for routine qualitative and quantitative analyses of synthetic antioxidants and preservatives in edible vegetable oils.     

胶束电动色谱在线推扫富集技术测定饮料中的防腐剂苯甲酸

考察了样品预处理、背景缓冲溶液pH、十二烷基硫酸钠（SDS）浓度、进样时间对苯甲酸测定过程中的富集效果的影响。结果显示：在电泳缓冲溶液为20mmol／L硼砂＋60mmol／L十二烷基硫酸钠（pH=9．30），紫外检测波长214nm，分离电压18kV时，富集倍数可达150倍。在线推扫富集胶束电动色谱法减少了样品处理的繁琐过程，操作简单，成本低。大大缩短了分析周期，弥补了毛细管电泳测定微量组分的不足。     

Analysis of free and esterified sterols in edible oils by online reversed phase liquid chromatography-gas chromatography (RPLC-GC) using the through oven transfer adsorption desorption (TOTAD) interface

An online reversed phase liquid chromatography-gas chromatography (RPLC-GC) method is proposed to quantify free, total and esterified sterols of edible oils. To determine free sterols the diluted oils are injected into the liquid chromatograph, where free sterols are separated from triglycerides and the sterol fraction is automatically transferred to the gas chromatograph to be analysed. To determine total sterols the samples were saponified with potassium hydroxide in ethanolic solution and the unsaponifiable fraction was extracted with diethyl ether. The extract was then analysed by RPLC-GC, avoiding the laborious thin layer chromatography step used in the Official European Union (EU) Method. The relative standard deviations (RSDs) from the absolute peak area varied from 7.6% to 15.8%. Limits of detection (LODs) were less than 8.5 mg/kg. No variability in retention time was observed. The method was applied to the determination of total sterols in edible oil samples and the results were compared with those obtained with the Official EU Method. Good agreement was found between both methods, except in the case of campesterol.     

食用植物油中残留溶剂测定的相平衡条件探讨

在采用非极性色谱柱对溶剂组分进行分离的基础上,对食用植物油残留溶剂顶空分析的相平衡条件进行研究.静态顶空分析的灵敏度主要取决于由平衡温度、平衡时间、气液相体积比所决定的气相提取效率,平衡温度显著影响分析的灵敏度,而平衡时间和气液相比例的选择性则不及平衡温度明显,提高平衡温度至溶剂沸点以上可以明显提高检测的灵敏度;通过实验得到优化的相平衡参数为:平衡温度为90℃、平衡时间为30 min、取样质量与汽化瓶体积的比值为1.0:2.5.     

Fatty acid esters of monochloropropanediol (MCPD) and glycidol in refined edible oils

Recently, fatty acid esters of monochloropropanediol (MCPD) and that of glycidol have been reported in refined edible oils. Since then a wealth of research has been published on the factors influencing the formation of these contaminants in foods. It can be noted that the predominant precursors in a given matrix will not necessarily be the same as in other matrices. Further, proven relationships in the past between precursors responsible for free MCPD or free glycidol formation will not necessarily be valid for their fatty acid-esterified counterparts. This review attempts to summarise the current status of the literature as it pertains to the reasons surrounding the manifestation of MCPD esters and glycidyl esters in oils and fats. Recent efforts to mitigate the levels of these contaminants were highlighted and put into the context of their respective reaction matrices. As more accurate occurrence data for MCPD esters and glycidyl esters in other foods are collected, more targeted mitigation experiments can be formulated with respect to the reaction matrices under investigation.     

凝胶渗透色谱-高效液相色谱法检测食用油中邻苯二甲酸酯类的含量

建立了以凝胶渗透色谱（GPC）和高效液相色谱（HPLC）联用技术检测食用油中邻苯二甲酸酯类含量的方法。样品经GPC处理后,采用乙腈/水体系为流动相,ODS柱分离,PDA检测器检测,检测波长224nm。实验结果：该方法在0.1～8.0mg/L范围内线性关系良好;DMP、DEP、BBP、DBP、DNOP的仪器检出限（S/N=3）分别为10、10、25、50、50μg/L,低、中、高三个浓度水平的回收率均在95%～110%之间。结论：该方法准确可靠,精密度较高。