High performance liquid chromatographic separation of cholesterol oxidation products

Summary A fast, sensitive, high performance liquid chromatographic method for the simultaneous determination of cholesterol hydroperoxides and other major oxysterols, using two different detection systems (ultraviolet at 210 nm and light scattering), is here described. The hydroperoxy derivatives were obtained by cholesterol photoxidation, isolated by thin layer chromatography and joined with a standard mixture of 10 oxysterols (epoxy, hydroxy and keto derivatives). Aliquots were directly injected onto a 5-μm particle size, 25×0.46 cm i.d. Spherisorb S5 CN normal phase column, usingn-hexane/anhydrous ethanol (97:3, v/v) as mobile phase and a flow rate of 0.8 mL min⁻¹. This method allowed, in a single isocratic analysis, the separation and quantification of the primary and secondary cholesterol oxidation products in 30 minutes. The light scattering detector was particularly useful for the determination of nonderivatized 5,6-epoxides and cholestane-3β,5α,6β-triol. The sensitivity of both detectors was very similar for most of the oxysterols, except for the 5,6-epoxides and the 7-ketocholesterol. The method suitability for the determination of cholesterol oxidation products in food matrices was successfully tested on a saponified lipid extract from egg yolk powder.     

A rapid gas chromatographic method for the analysis of acidic fermentation products

Summary A rapid and simple method for the identification of acidic fermentation products is described. Methyl esters of volatile and non-volatile acids are separated on a single chromatographic column. Retention time data for a number of acids are tabulated.     

气相色谱-质谱法测定酱猪蹄和酱猪肘中5种胆固醇氧化物

建立了气相色谱-质谱（GC-MS）测定酱猪蹄和酱猪肘中7 β-羟基胆固醇、5 α，6 α-环氧化胆固醇、胆甾烷-3 β，5 α，6 β-三醇、25-羟基胆固醇和7-酮基胆固醇5种胆固醇氧化物（COPs）含量的方法。样品经甲醇-氯仿（1：2，v/v）混合溶液提取，硅胶固相萃取小柱净化后，加入N，O-双（三甲基硅基）乙酰胺-三甲基氯硅烷-三甲基硅基咪唑（3：2：3，v/v/v）（Sylon BTZ）进行衍生化处理，设置合理的柱温升温程序，采用选择离子扫描（SIM）模式进行检测。在优化条件下，5种COPs在22 min内实现分离，且分离度良好。5种COPs的线性范围满足测定要求，3个加标水平下的平均回收率为61.16%~96.96%，相对标准偏差≤ 7.80%（n=3），检出限（以信噪比为3计）和定量限（以信噪比为10计）分别为0.02~47.07 ng/g和0.06~156.90 ng/g。该法快速简便，线性范围广，灵敏度高，可作为测定实际样品中COPs的有效方法。     

Automated headspace solid‐phase microextraction and on‐fiber derivatization for the determination of clenbuterol in meat products by gas chromatography coupled to mass spectrometry

A method was developed for the determination of clenbuterol in meat using stable‐isotope‐dilution gas chromatography with mass spectrometry coupled with solid‐phase microextraction and on‐fiber derivatization. The samples were first homogenized with hydrochloric acid followed by protein deposition. After headspace solid‐phase microextraction and on‐fiber derivatization, the content of clenbuterol was measured with the aid of stable‐isotope dilution. The condition of solid‐phase microextraction was optimized by central composite design. The relative standard deviations, limit of detection, and recoveries for clenbuterol were 4.2–9.2%, 0.48 μg/kg, and 96–104%, respectively. The proposed method was satisfactory for analysis of real samples as compared with the Chinese standard method.     

GC-MS characterization and quantification of sterols and cholesterol oxidation products

Summary A GC-MS method has been studied for characterization and quantification of phytosterols, cholesterol and cholesterol oxidation products. Baseline separations have been achieved between cholesterol, cholesterol 5-6-epoxide, 5-cholestene-3-ol-7one (7-keto-cholesterol), cholestene-3-5-6-triol, 5-cholestene-3-25-diol (25-hydroxycholesterol), 5-cholestene-3-20-diol (20-hydroxycholesterol), 5-cholestene-3-7-diol (7-hydroxycholesterol) and 5-cholestene-3-19-diol (19-hydroxycholesterol) as well as between -cholestane, cholesterol, stigmasterol, campesterol and -sitosterol. Excellent linearity of response has been obtained permitting reliable quantification. The characterization of each derivatized sterol has been performed by mass-spectrometry. The results confirm the utility of combined gas chromatography-mass spectrometry in the analysis and characterization of sterols and cholesterol oxidation products.     

Analysis of cholesterol oxidation products by Fast gas chromatography/mass spectrometry

The aim of the present study was to set‐up a Fast gas chromatography/mass spectrometry method for the analysis of cholesterol oxidation products (COPs). A silylated mixture of seven oxysterol standards was injected into a Fast GC/MS system. A capillary GC column (10 m×0.1 mm internal diameter×0.1 μm film thickness) coated with 95% dimethyl‐ and 5% diphenyl‐polysiloxane, was used. The method gave a fast (total analysis time=3.5 min) and satisfactory resolution (R>1.2) of the COPs standards, with a good repeatability and sensitivity, similar to those of conventional GC/MS; recoveries were tested on mice liver. Fast GC/MS method suitability for COPs analysis in food was also tested on an oxidized sardine fillet, which had been previously saponified and purified by NH₂ solid‐phase extraction (SPE); a good repeatability and sensitivity was also obtained. The analytical performance of the Fast GC/MS method for the determination of COPs, together with the consequent significant reduction of the analysis time and consumables, demonstrates that Fast GC/MS represents a valid alternative to conventional GC/MS and evinces the great potential of such an analytical technique, which could be applied for both food and biological samples.     

Derivatization-independent cholesterol analysis in crude lipid extracts by liquid chromatography/mass spectrometry: applications to a rabbit model for atherosclerosis

Direct measurement of various sterols in crude lipid extracts in a single experiment from limited biological samples is challenging. Current mass spectrometry (MS) based approaches usually require chemical derivatization before subjecting to MS analysis. Here, we present a derivatization-independent method for analyzing various sterols, including cholesterol and its congeners, using liquid chromatography and atmospheric pressure chemical ionization mass spectrometry. Based on the specific tandem mass spectrometry pattern of cholesterol, multiple reaction monitoring (MRM) transitions were used to quantify free cholesterol and its fatty acyl esters. Several cholesterol oxidation products could also be measured using the upfront liquid chromatography separation and specific MRM transitions. The method was validated alongside established enzymatic assays in measuring total cholesterol. As a proof of concept, we analyzed plasma sterols in rabbits administrated with a high cholesterol diet (HCD) which is a classical atherosclerotic model. Free cholesterol, cholesterol esters, 7-hydroxycholesterol, and 7-ketocholesterol were elevated in plasma of rabbits on HCD. This method could also serve as an excellent tool for quantitative analysis of other sterols such as ergosterol and sitosterol in other organisms beside mammalian. In Saccharomyces cerevisiae, our results indicated dramatic increases of the ratio of ergosterol esters to free ergosterol in both yeh2Δ and tgl1Δ cells, which are consistent with the function of the respective enzymes.     

HPLC测定一次性塑料用品中邻苯二甲酸酯类增塑剂

本文用高压、液体色谱柱Liehmspher C-18(250mm×4.6mmID,5μm),以乙腈-水为流动相,流速为1.0mL/min,线性梯度乙腈从70%到100%,采用质谱检测器对邻苯二甲酸酯进行定性鉴定.邻苯二甲酸二甲脂(DMP)、邻苯二甲酸二乙酯(DEP)、邻苯二甲酸二丁酯(DBP)和邻苯二甲酸二甲酸辛酯(DOP)浓度分别为1.1～89mg/L,0.9～74mg/L,0.9～71mg/L和0.9～68mg/L时线性关系良好,平均回收率分别为83%,89%,86%,87%(n=5).建立了准确度和灵敏度高,方便快捷有效的一次性塑料用品中邻苯二甲酸酯类增塑剂的高效液相色谱定量分析方法.     

气相色谱法研究胶体金负载纳米金属氧化物催化氧化CO行为

将胶体金负载于不同的金属氧化物纳米材料上,分别制备了Au/TiO2、Au/γ-Al2O3、Au/Fe2O3和Au/ZnO纳米材料,采用透射电子显微镜(TEM)对负载前后的材料进行了表征。利用气相色谱法检测CO的浓度,在选定的色谱条件下,5 min内就实现了快速分离测定,该检测方法的线性范围为1.0×10-6%~10%(体积分数),回收率为96.0%~103.6%,精密度为1.2%~2.3%。应用自制的催化活性评价装置对氧化物纳米材料催化氧化CO的行为进行了研究,结果表明:负载金氧化物纳米材料催化氧化CO的性能在50~200℃均优于相应的未负载金的材料,其中Au/TiO2的催化氧化效果最佳,且在一定气体流速范围内具有稳定的催化活性。     

衍生-气相色谱法测定水产品中的游离甲醛

建立了水产品中游离甲醛残留量的衍生-气相色谱快速检测方法,对衍生剂、抗干扰剂、萃取剂、色谱条件进行了研究.用HP-5 (30 m×0.32 mm i.d.,0.25 μm)毛细管色谱柱,程序升温,γ-ECD检测器,外标法定量.甲醛的检出限为0.05 mg/kg,在0.1～20.0 mg/L范围内,其线性相关系数R2=0.9994,标准偏差为0.041,在0.5、 1.5、 5.0 mg/kg 3个添加水平下回收率为89.6%～102.6%.3个实验室间的RSD为2.7%～4.4%.     

Determination of cholesterol in milk fat by gas chromatography with direct injection and sample saponification

Summary A rapid and direct gas chromatographic (GC) method for determining free cholesterol in milk fat using a capillary column and programmed-temperature vaporizer-injector was assayed. It was compared with other procedures involving saponification of fat, solvent extraction of unsaponifiable matter — with and without fractionation by thin-layer chromatography — and transformation of sterols into silyl derivatives prior to GC analysis. This paper proposes an alternative to other published procedures. Repeatability of the method was assessed and the coefficient of variation determined as 2.1 %. The alternative saponification method exhibited comparable accuracy (coefficient of variation=1.8 %). Recovery ranged from 99.1 % to 105.6 %.     

Determination of cholesterol in milk fat by gas chromatography with direct injection and sample saponification

Summary A rapid and direct gas chromatographic (GC) method for determining free cholesterol in milk fat using a capillary column and programmed-temperature vaporizerinjector was assayed. It was compared with other procedures involving saponification of fat, solvent extraction of unsaponifiable matter—with and without fractionation by thin-layer chromatography—and transformation of sterols into silyl derivatives prior to GC analysis. This paper proposes an alternative to other published procedures. Repeatability of the method was assessed and the coefficient of variation determined as 2.1%. The alternative saponification method exhibited comparable accuracy (coefficient of variation=1.8%). Recovery ranged from 99.1% to 105.6%.     

顶空气相色谱法快速测定肉及肉制品中乙烯利的残留量

利用乙烯利在碱性水溶液中受热能够快速分解成乙烯的特性,建立了顶空气相色谱法快速测定乙烯利在肉及肉制品中残留量的方法。在样品中添加碱液后恒温加热,吸取顶空瓶中的上层气体,采用石英毛细管色谱柱分离,氢火焰离子化检测器测定。该方法的检测限为0.01mg/kg,回收率为90.9%～96.0%,相对标准偏差为3.5%～8.5%。适用于猪肉、牛肉、鸡肉等肉及肉制品中乙烯利残留量的检测。     

Development and validation of a gas chromatographic method for analysis of fosfomycin in chicken muscle samples

Summary A gas chromatographic method for the determination of residues of Fosfomycin in chicken muscle samples has been developed. Muscle samples were homogenised with TRIS buffer, containing phenylphosphonic acid (as internal standard) and Fosfomycin using a tissue homogenizer. Afterwards, the samples were ultrafiltered and the ultrafiltrate was evaporated to dryness. A silylation reagent for derivatization was used in order to reconstitute the residue. The linear concentration range of application was 10–150 μgg⁻¹, with a detection and quantitation limit of 3.11 and 10 μgg⁻¹, respectively. The method was efficient with a mean recovery of 87.83% from spiked muscle. The results obtained show that gas chromatography is a useful method for the determination of Fosfomycin residues in chicken muscle samples.     

Development of a carbohydrate silylation method in ionic liquids for their gas chromatographic analysis

This paper reports on the feasibility of silylation of low molecular weight carbohydrates dissolved in different ionic liquids (ILs) for their further analysis by gas chromatography (GC). Derivatization reagents (nature and amounts), temperature and time of reaction and stirring conditions were evaluated for different carbohydrates (i.e., glucose, mannose, fructose and lactose) dissolved in 1-ethyl-3-methylimidazolium dicyanamide [EMIM][DCA]. Evaluation of conformational isomerism of glucose dissolved in [EMIM][DCA] revealed the effect of the time of dissolution in the equilibration of α- and β-furanoses (up to 3% and 6%, respectively, after 70 h of incubation) and that 21 h sufficed to obtain results similar to those provided by the reference method involving pyridine. Once optimized, the proposed derivatization procedure provided satisfactory yields (i.e., close to 100%) using 100 μL of trimethylsilylimidazole (TMSI) at mild conditions (25 °C) for a relatively short time (1 h) for most of the investigated carbohydrates. Under these experimental conditions, linear responses (i.e., R² better than 0.974) were obtained in the tested range of 0.25–1 mg of the derivatized target compounds. Other reagents, such as N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) + 1% trimethylchlorosilane (TMCS), were successfully used under ultrasonic conditions for aldose monosaccharides and disaccharides derivatization, while BSTFA was useful for ketose monosaccharides. The possibility of using the proposed method for the derivatization of selected carbohydrates dissolved in different ILs and the efficiency of the method applied to the analysis of carbohydrates present in real samples (fruit juices) have also been investigated.     

Quick gas chromatographic method for determining common pesticides in musts and wines

Summary A rapid method based on gas chromatography which determines parathion-methyl, fenitrothion, chlorpyrifos, dichlofluanid, vinclozolin, chlozolinate, procymidone and iprodione is described. It involves quantitative extraction with n-hexane and determination by capillary gas chromatography using an electron capture detector. Pesticides were satisfactorily separated in 15 min with a phenylmethylsilicone fused-silica capillary column under isothermal conditions. Quantitation was carried out using dieldrin as internal standard. The method seems appropriate for oenological laboratory work because of its simplicity and rapidity. It was successfully used to identify and quantify pesticides studied in musts and wines.     

Direct detection of trimethylamine in meat food products using ion mobility spectrometry

Biogenic amines are degradation products generated by bacteria in meat products. These amines can indicate bacterial contamination or have a carcinogenic effect to humans consuming spoiled meats; therefore, their rapid detection is essential. Trimethylamine (TMA) is a good target for the detection of biogenic amines because its volatility. TMA was directly detected in meat food products using ion mobility spectrometry (IMS). TMA concentrations were measured in chicken meat juice for a quantitative evaluation of the meat decaying process. The lowest detected TMA concentration in chicken juice was 0.6 ± 0.2 ng and the lowest detected signal for TMA in a standard aqueous solution was 0.6 ng. IMS data were processed using partial least squares (PLS) and Fuzzy rule-building expert system (FuRES). Using these two chemometric methods, trimethylamine concentrations of different days of meat spoilage can be separated, indicating the decaying of meat products. Comparing the two methods, FuRES provided a better classification of different days of meat spoilage.     

New clean-up method for gas chromatographic analysis of pyrethroid residues

Summary A fast and efficient method has been developed for clean-up of fenpropathrin and fluvalinate for gas chromatographic determination of their residues in crops, grain and soil. Charcoal (Darco-G-60) was used as adsorbent and the pyrethroids recovered by washing the adsorbent with hexane-acetone (9∶1). The method provides a clear filtrate with no interfering peaks in the chromatogram. Recoveries ranged 91.00–100%.     

固相萃取-抑制电导离子色谱法测定水产品中有机酸

建立了梯度淋洗-抑制型电导离子色谱法检测水产品中有机酸的方法。在2～3个数量级范围内,该方法对目标化合物的检测线性良好。酒石酸的线性范围为15～500 ng/mL,检测限为0.05 mg/kg;柠檬酸线性范围为8～500 ng/mL,检测限为0.03 mg/kg。以大黄鱼、中华绒螯蟹、南美白对虾、文蛤为空白样品,加入酒石酸和柠檬酸质量分数分别为0.05,0.07和0.10 mg/kg,酒石酸的加标回收率介于84.4%～89.2%,RSD<6.5%,柠檬酸的加标回收率介于87.5%～93.8%,RSD<5.9%。