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.     

Residue analysis of melamine in milk products by micellar electrokinetic capillary chromatography with amperometric detection

A high-performance micellar electrokinetic capillary chromatography with amperometric detection (MECC–AD) method for the fast determination of melamine (MM), occasionally used to increase the apparent protein content of milk products, has been developed. Method development involved optimisation of the working electrode, the running buffer system and acidity, the concentration of sodium dodecyl sulphate (SDS), the separation voltage, the applied potential and the sample injection time. Under the optimum conditions, MM can be well separated from its co-existing interferences in real-world samples within 9 min at the separation voltage of 20 kV in a 8 mmol/L SDS/20 mmol/L H₃BO₃–Na₂B₄O₇ running buffer (pH 7.4). Satisfactory recovery (83.3–105.5%), repeatability of the peak current (3.2%) and migration time (3.8%), and the limit of detection (2.1 × 10⁻⁶ g/mL) for the method were achieved. This proposed procedure has been successfully used for the determination of MM in milk products.     

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.     

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.     

Cloud-point extraction and reversed-phase high-performance liquid chromatography for the determination of synthetic phenolic antioxidants in edible oils

A cloud-point extraction (CPE) method using Triton X-114 (TX-114) nonionic surfactant was developed for the extraction and preconcentration of propyl gallate (PG), tertiary butyl hydroquinone (TBHQ), butylated hydroxyanisole (BHA), and butylated hydroxytoluene (BHT) from edible oils. The optimum conditions of CPE were 2.5% (v/v) TX-114, 0.5% (w/v) NaCl and 40 min equilibration time at 50 °C. The surfactant-rich phase was then analyzed by reversed-phase high-performance liquid chromatography with ultraviolet detection at 280 nm, using a gradient mobile phase consisting of methanol and 1.5% (v/v) acetic acid. Under the studied conditions, 4 synthetic phenolic antioxidants (SPAs) were successfully separated within 24 min. The limits of detection (LOD) were 1.9 ng mL(-1) for PG, 11 ng mL(-1) for TBHQ, 2.3 ng mL(-1) for BHA, and 5.9 ng mL(-1) for BHT. Recoveries of the SPAs spiked into edible oil were in the range 81% to 88%. The CPE method was shown to be potentially useful for the preconcentration of the target analytes, with a preconcentration factor of 14. Moreover, the method is simple, has high sensitivity, consumes much less solvent than traditional methods, and is environment-friendly. Practical Application: The method established in this article uses less organic solvent to extract SPAs from edible oils; it is simple, highly sensitive and results in no pollution to the environment.     

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.     

加压毛细管电色谱法同时测定植物油中4种抗氧化剂

采用加压毛细管电色谱-紫外检测,建立了一种适用于植物油中常见抗氧化剂的分离检测方法。使用1.8μm粒径的C18毛细管色谱柱,以乙腈-水（0.05%甲酸）为流动相进行梯度洗脱,泵流速为0.05m L/min,分流比为1∶200,分离电压为15k V,没食子酸丙酯（PG）、叔丁基对苯二酚（TBHQ）、丁基羟基茴香醚（BHA）、2,6-二叔丁基对甲酚（BHT）四种抗氧化剂可在8min内实现快速分离。各组分的检出限（S/N=3）分别为0.6、2.0、3.0、5.5μg/m L,线性关系良好,样品加标回收率在93.5%¹08.0%之间,RSD在0.3%¹.3%之间。将所建立方法应用于植物油样品的分析,取得了良好的分析结果。      

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.     

Determination of seven preservatives in cosmetic products by micellar electrokinetic chromatography

A micellar electrokinetic chromatography method using cetyltrimethylammonium bromide (CTAB) as a cationic surfactant, coupled with UV–Vis detection, was developed for the simultaneous determination of seven preservatives, including methyl‐, ethyl‐, propyl‐ and butyl‐paraben and phenol, phenoxyethanol and resorcinol. The method involved optimizing the pH of the phosphate buffer and concentrations of CTAB, ethanol and 2‐hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD). The preservatives were well separated using optimum conditions and separated within 10 min at a separation voltage of ?12.5 kV with the 1.0 mM phosphate buffer (pH 7.0) containing 90 mM CTAB, 25 mM HP‐β‐CD and 10% (v/v) ethanol. Satisfactory recoveries (84.1–103.0%), migration time (RSD < 3.1%) and peak area (RSD < 4.5%) repeatabilities were achieved. Detection limits of the preservatives were between 0.31 and 1.52 μg mL^?1 (S/N = 3, n = 5). The optimized method was successfully applied to the simultaneous determination of these preservatives in 10 commercial cosmetic products.     

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.     

Micellar electrokinetic capillary chromatography of methylxanthines‐containing beverages: discussion of the molecular species involved

Micellar electrokinetic capillary chromatography (MECC) experimental conditions were applied to 12 samples of methylxanthine‐containing infusions of different commercial brands of yerba mate, coffee, tea and cocoa as well as two cola drinks. The best resolution in this mode of automated high‐performance capillary electrophoresis (HPCE) was achieved here when using 15 kV voltage in an uncoated fused‐silica capillary of 45 cm length (40 cm effective length), 50 mM sodium dodecylsulfate, 90 mM pH 8.5 borate buffer and UV detection. Theobromine, caffeine and theophylline were separated, and the peak splitting due to tautomeric species was observed. Experimental conditions were controlled, keeping constant the size of the elution window in each analysis. The limit of detection was less than 1 mg l^?1, the limit of quantitation was 2.5 mg l^?1 and the work range was 2.5–300 mg l^?1. This HPCE–MECC system has proved suitable for the analysis/quality control of xanthines in beverages for consumption. Roles of various parameters as well as distinctly charged species of each xanthine and the origin of peak splitting in this MECC system are discussed. Copyright © 2004 Society of Chemical Industry     

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.     

高效液相色谱法检测食用油中的丙二醛

建立了柱前衍生高效液相色谱检测食用油中丙二醛的方法。样品中的丙二醛用三氯乙酸溶液提取后与硫代巴比妥酸(TBA)进行衍生化反应后,采用液相色谱分离,荧光检测器测定。在优化的条件下,丙二醛的检出限为0.02mg/kg,回收率在87.1%~103.2%之间,相对标准偏差小于6%。该方法具有操作简单、灵敏度高等特点,适用于食用油中丙二醛的测定。      

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.     

顶空气相色谱法快速测定食用植物油中 有机溶剂残留量的研究

目的建立了顶空气相色谱法检测食用植物油中有机溶剂残留量的分析方法。方法研究了进样的平衡温度、平衡时间,采用优化后的色谱条件,使溶剂残留中的各组分完全分离,减少基质影响,通过记录分离的各组分峰面积,采用归一化法进行定量。结果在2 mg/kg~200 mg/kg浓度范围内,线性关系良好,线性方程为Y=17.4427X+44.4790,R2=0.9999。采用低中高三个浓度的加标回收率均在99.1%~105.0%,相对标准偏差小于3.0%。结论该方法简便、快速、准确,可适用于食用植物油中有机溶剂残留的测定,便于推广应用。