Sensitive Determination of Five Priority Haloacetic Acids by Electromembrane Extraction with Capillary Electrophoresis

A method for sensitive determination of five priority haloacetic acids in drinking water has been developed for the first time based on electromembrane extraction (EME) prior to CZE with capacitively coupled contactless conductivity detection (CZE‐C⁴D). The target analytes were extracted from 10 mL of the sample solution (donor phase), through the supported liquid membrane (using a polypropylene membrane supporting 1‐octanol), and into 10 µL of 50 mmol/L NaAc solution (acceptor phase). The extracted solution was directly analyzed by CZE‐C⁴D without derivatization. Several factors that affect separation, detection and extraction efficiency were investigated. Under the optimum conditions, five haloacetic acids (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid) could be well separated from other components coexisting in water samples within 23 min, exhibiting a linear calibration over two orders of magnitude (r?0.9943); the enrichment factors at 430–671 were obtained in a 30 min of extraction, and the limits of detection were in the range of 0.17–0.61 ng/mL. The intraday relative standard deviations for peak areas investigated at 10 ng/mL were between 1.2% and 9.7% for the combined EME‐CZE‐C⁴D procedure. This approach offers an attractive alternative to the officially proposed method for purified drinking water analysis, which requires derivatization procedure prior to gas chromatography analysis.     

Impact on lipid membrane organization by free branched-chain fatty acids

Here, we exploit the non-invasive techniques of solid-state NMR (nuclear magnetic resonance) and differential scanning calorimetry (DSC) to study the effect of free iso and ante-iso branched chain fatty acids (BCFAs) on the physicochemical properties of lipid membranes. Free fatty acids are present in biological membranes at low abundance, but can influence the cellular function by modulating the membrane organization. Solid state NMR spectra of dimyristoylphosphatidylcholine (DMPC) lipid membranes containing either free 12-methyltetradecanoic acid (a15:0) or free 13-methyltetradecanoic acid (i15:0), show significant differences in their impact on the lipid bilayer. Chain order profiles obtained by deuterium NMR on fully deuterated DMPC-d(67) bilayers revealed an ordering effect induced by both fatty acids on the hydrophobic membrane core. This behavior was also visible in the corresponding DSC thermograms where the main phase transition of DMPC bilayers-indicative of the hydrophobic membrane region-was shifted to higher temperatures, with the iso isomer triggering more pronounced changes as compared to the ante-iso isomer. This is probably due to a higher packing density in the core of the lipid bilayer, which causes reduced diffusion across membranes. By utilizing the naturally occurring spin reporters nitrogen-14 and phosphorus-31 present in the hydrophilic DMPC headgroup region, even fatty acid induced changes at the membrane interface could be detected, an observation reflecting changes in the lipid headgroup dynamics.     

Simultaneous determination of amounts of major phospholipid classes and their fatty acid composition in erythrocyte membranes using high-performance liquid chromatography and gas chromatography.

A method for the simultaneous determination of amounts of major phospholipid classes and their fatty acid composition in erythrocyte membranes is described. The method consists in extraction of phospholipids from erythrocyte membranes, separation of phospholipid classes by high-performance liquid chromatography, methylation of phospholipids and determination of phospholipid-bound fatty acids by capillary gas chromatography. The amounts of phospholipid classes are calculated from the total weight of phospholipid-bound fatty acids and their average molecular weights. The method was applied to erythrocytes from rats. The results show that the method is reproducible and is useful for the determination of amounts of phospholipid classes and their fatty acid composition in small blood samples.     

Hydrogel Membrane Improves Batch‐to‐Batch Reproducibility of an Enzymatic Glucose Biosensor

A permselective membrane is a critical component that defines the linear detection limits, the sensitivity, and thus the ultimate efficacy of an enzymatic biosensor. Although membranes like epoxy‐polyurethane (epoxy‐PU) and Nafion are widely used and provide the desired glucose detection limits of 2 to 30 mM, both the within batch and batch‐to‐batch variability of sensors that use these materials is a concern. The hypothesis for this study was that a crosslinked hydrogel would have a sufficiently uniform porosity and hydrophilicity to address the variability in sensor sensitivity. The hydrogel was prepared by crosslinking di‐hydroxyethyl methacrylate, hydroxyethyl methacrylate and N‐vinyl pyrrolidone with 2.5 mol% ethylene glycol dimethacrylate using water soluble initiators – ammonium persulfate and sodium metabisulfite under a nitrogen atmosphere. The hydrogel was applied to the sensor by dip coating during polymerisation. Electrochemical measurements revealed that the response characteristics of sensors coated with this membrane are highly consistent. Scanning electrochemical microscopy (SECM) was used to spatially resolve glucose diffusion through the membrane by measuring the consequent H₂O₂ release and compared with an epoxy‐PU membrane. Hydrogen peroxide measurements using SECM revealed that the epoxy‐PU membranes had uneven lateral diffusion profiles compared to the uniform profile of the hydrogel membranes. The uneven diffusion profiles of epoxy‐PU membranes are attributed to a fabrication method that results in uneven membrane properties, while the uniform diffusion profiles of the hydrogel membranes are primarily dictated by their uniform pore size.     

基于气相色谱-质谱的拟靶向代谢组学方法分析大米中脂肪酸

建立了一种基于气相色谱-质谱的拟靶向代谢组学分析方法对大米中脂肪酸进行分析,共检测到16种脂肪酸,并研究了不同大米中脂肪酸的轮廓差异。以提取到饱和脂肪酸和不饱和脂肪酸的总量为评价指标,比较了6种提取方法及4种提取溶剂对脂肪酸提取效率的影响。将该方法用于5种不同大米（稻花香、吉星、金浪子、农大、状元）中脂肪酸的分析,发现稻花香大米中脂肪酸轮廓与其他4种均有较大差异;而金浪子与农大、状元间脂肪酸差异也较大,与吉星脂肪酸轮廓较为相似。该方法简单,有较好的稳定性和准确性,可为大米品质和营养价值改善研究提供基础数据。     

Fatty acid composition of human erythrocyte membranes by capillary gas chromatography-mass spectrometry

Capillary gas chromatographic and gas chromatographic--mass spectrometric methods were employed for profiling total fatty acid content of human erythrocyte membranes. The protocol was designed to efficiently separate, identify, and accurately quantify the fatty acid composition in human erythrocyte membranes. Washed erythrocyte "ghosts" were saponified in aqueous methanolic sodium hydroxide solution and methylated with boron trichloride and acid catalysis. Extracted total fatty acid methyl esters (FAMEs) were analyzed using a highly polar cyanopropylsiloxane SP 2560 fused-silica capillary column. Total run time was 55 min, and 45 FAMEs were tentatively identified by relative retention times compared to those of known FAMEs. Confirmation of identities by mass spectral structure elucidation revealed saturated, mono- and polyunsaturated, and branched-chain FAMEs. The presence of four fatty aldehydes was also confirmed as dimethyl acetal derivatives. Identification of cis/trans isomers was based on relative retention times and characteristic profile of the cis/trans FAME standard. Quantification of FAMEs for normal subjects showed some variation in relative amounts, consistent with expectations based on literature reports on total or phospholipid FAMEs from human erythrocytes. Separation of individual components of fatty acid families (n-3), (n-6), and (n-9) is demonstrated. Losses in relative amounts of polyunsaturated fatty acids upon storing samples were also detectable by this rapid method.     

Fatty acid profiling of raw human plasma and whole blood using direct thermal desorption combined with gas chromatography-mass spectrometry

Gas chromatography (GC) has in recent times become an important tool for the fatty acid profiling of human blood and plasma. An at-line procedure used in the fatty acid profiling of whole/intact aquatic micro-organisms without any sample preparation was adapted for this work. A direct thermal desorption (DTD) interface was used to profile the fatty acid composition of human plasma and whole human blood of eight volunteers in a procedure omitting the usual lipid extraction steps that precede sample methylation in the traditional (off-line) protocols. Trimethylsulfonium hydroxide (TMSH) was used as reagent for thermally assisted methylation. In a fully automated manner, the liner of the GC injector is used as a sample-and-reaction container with the aid of the DTD interface. The fatty acid methyl ester (FAME) profiles obtained using this novel approach, were very identical to those obtained when the traditional off-line protocol was applied. FAME yields obtained in the at-line DTD method were found to be very similar for saturated fatty acids, but significantly higher for polyunsaturated fatty acids compared to off-line yields. As a result of the contribution of circulating cell membranes in blood, substantial differences were observed when the amount of FAMEs obtained in whole human blood and human plasma samples were compared after their analysis. Thanks to the fully automated operation of this novel procedure, large series of analyses can easily be performed.     

Separation of Nile Blue-labelled fatty acids by CE with absorbance detection using a red light-emitting diode

The separation of fatty acids derivatised with Nile Blue (NB) by CE with detection using a red light-emitting diode (LED) was examined. NB was selected as the derivatisation agent due to its high molar absorption coefficient of 76,000 M(-1) cm(-1) at 633 nm, making it well suited for sensitive absorbance detection using a red 635 nm LED. NB-labelled fatty acids were separated by both MEKC using SDS micelles, i-PrOH and n-BuOH and by NACE in a number of solvents including MeOH, EtOH and ACN. The sensitivity of NACE was superior to MEKC, with detection limits of 5x10(-7)-7x10(-7) M obtained for each acid, approximately 20 times lower than the MEKC method. The NACE detection limits are approximately 100 times lower than previous reports on the separation of fatty acids by CE using indirect absorbance detection, ten times lower than using indirect fluorescence detection and are inferior only to those obtained using precapillary derivatisation and direct fluorescence detection. The efficiency of the NACE method was also superior to MEKC and allowed the separation of unsaturated fatty acids to be examined, although it was not possible to baseline-resolve linoleic (C18:2) and linolenic (C18:3) acids in a reasonable time. The method was used to analyse the fatty acid profile of two edible oils, namely sunflower and sesame oils, after alkali hydrolysis, where it was possible to identify both the saturated and unsaturated fatty acids in each sample.     

New application of a subcellular fractionation method to kidney and testis for the determination of conjugated linoleic acid in selected cell organelles of healthy and cancerous human tissues

To clarify the mechanism of the anticarcinogenic effect of conjugated linoleic acid (CLA), its intracellular distribution needs to be determined. Subcellular fractionation using centrifugation techniques is a method that is frequently used for isolation of cell organelles from different tissues. But as the size and density of the organelles differ, the method needs to be optimised for every type of tissue. The novelty of this study is the application of a subcellular fractionation method to human healthy and cancerous renal and testicular tissue. Separation of total tissue homogenate into nuclei, cytosol, and a mixture of mitochondria and plasma membranes was achieved by differential centrifugation. As mitochondria and plasma membranes seemed to be too similar in size and weight to be separated by differential centrifugation, discontinuous density-gradient centrifugation was carried out successfully. The purity of the subcellular fractions was checked by measuring the activity of marker enzymes. All fractions were highly enriched in their corresponding marker enzyme. However, the nuclear fractions of kidney and renal cell carcinoma were slightly contaminated with mitochondria and plasma membrane fractions of all tissues with lysosomes. The fraction designated the cytosolic fraction contained not only cytosol, but also microsomes and lysosomes. The CLA contents of the subcellular fractions were in the range 0.13–0.37% of total fatty acids and were lowest in the plasma membrane fractions of all types of tissue studied. C16:0, C18:0, C18:1 c9, C18:2 n-6, and C20:4 n-6 were found to be the major fatty acids in all the subcellular fractions studied. However, marked variations in fatty acid content between subcellular fractions and between types of tissue were detectable. Because of these differences between tissues, no general statement on characteristic fatty acid profiles of single subcellular fractions is possible.     

Simultaneous analysis of ten low‐molecular‐mass organic acids in the tricarboxylic acid cycle and photorespiration pathway in Thalassiosira pseudonana at different growth stages

A method using high‐performance liquid chromatography coupled with tandem mass spectrometry was developed for the simultaneous determination of organic acids in microalgae. o‐Benzylhydroxylamine was used to derivatize the analytes, and stable isotope‐labeled compounds were used as internal standards for precise quantification. The proposed method was evaluated in terms of linearity, recovery, matrix effect, sensitivity, and precision. Linear calibration curves with correlation coefficients >0.99 were obtained over the concentration range of 0.4–40 ng/mL for glycolic acid, 0.1–10 ng/mL for malic acid and oxaloacetic acid, 0.02–2 ng/mL for succinic acid and glyoxylic acid, 4–400 ng/mL for fumaric acid, 20–2000 ng/mL for isocitric acid, 2–200 ng mL⁻¹ for citric acid, 100–10000 ng mL⁻¹ for cis‐aconitic acid, and 1–100 ng mL⁻¹ for α‐ketoglutaric acid. Analyte recoveries were between 80.2 and 115.1%, and the matrix effect was minimal. Low limits of detection (0.003–1 ng/mL) and limits of quantification (0.01–5 ng/mL) were obtained except cis‐aconitic acid. Variations in reproducibility for standard solution at three different concentrations levels were <9%. This is the first report of the simultaneous analysis of ten organic acids in microalgae, which promotes better understanding of their growth state and provides reference value for high‐yield microalgae cultures.     

Differences in the fatty acid composition of KB-cells and gingival keratinocytes is culture medium additive dependent

The influence of culture medium additives foetal bovine serum (FBS), serum effective substitutes (SES) and human autologous serum on the fatty acid profile of KB-cells and human gingival keratinocytes was examined. The KB-cells were cultivated in RPMI medium added with FBS or SES and the gingival keratinocytes in D-MEM added with FBS or human autologous serum. Two days before the cells were prepared for gas chromatography (GC), the media were changed to serum- and antibiotic-free media. Whole fatty acids of the cells were analysed using GC and the fatty acid profiles were compared. KB-cells as well as gingival keratinocytes changed their fatty acid composition, according to the medium additive used. Significant differences were observed. In the case of KB-cells cultivated with SES the fatty acid changes suggest an increase of the membrane fluidity. Corresponding and significant differences were observed with gingival keratinocytes cultivated in medium added with human autologous serum: the membrane fluidity of the gingival keratinocytes was increased. It is supposed that an increased membrane fluidity caused by a different fatty acid spectrum of the host cell may relate to mechanisms of bacterial adhesion. Consequently, in vitro studies on invasion and adhesion of bacteria or virus are dependent on the medium used. Further analyses are necessary of the functional effects caused by differences in the content of specific FAs, especially with regard to the application of cultivated cells in the field of tissue engineering.     

Detection of malondialdehyde in vivo using microdialysis sampling with CE-fluorescence

Oxidative damage is a naturally occurring process where reactive oxygen species (ROS) attack and disrupt normal cellular function; however, these effects become elevated during a stress event, such as ischemia/reperfusion or seizure. One result of oxidative stress is lipid peroxidation, where ROS attack free unsaturated fatty acids forming lipid hydorperoxides, which then break down to form secondary products acrolein, 4‐hydroxynonenal, and malondialdehyde (MDA) resulting in irreversible membrane damage and ultimately cell death. Described here is a CE‐fluorescence method for the determination of MDA in conjunction with in vivo microdialysis sampling. MDA was derivatized with thiobarbituric acid under acidic conditions for 20 minutes and injected directly into the capillary without any pretreatment. This method provided a limit of detection of 25 nM (S/N=3) and a linear range of 25–2400 nM (1.8–174 ng/mL). This method was used to quantify MDA in rat heart, muscle, liver, and brain dialysate.     

ω‐3‐Fettsäuren: Prävention degenerativer Erkrankungen

It is well established, that nutrition plays a basic role in the prevention of typically chronic western diseases like cancer and atherosclerosis. So, the tendency of the nutrition science is to optimize nutrition. A modern concept of this idea is the design of functional foods. Widely used ingredients of functional foods are ω‐3 fatty acids, in particular the long chain fatty acids eicosapentaenic acid (EPA) and docosahexaenoic acid (DHA). Dietary ω‐3 fatty acids have effects on various physiological processes such as the fluidity of cell membranes, modulation of ion channels and the immune system. These effects are the basis of dietary supplementation with ω‐3 fatty acids in several diseases, like atherosclerosis. The usual German consumption habits lead to a deficiency of about 1 g EPA and DHA. Micro‐encapsulated oils with a high content of ω‐3 fatty acids added to functional foods could optimize the supply.     

Simultaneous determination of five triterpene acids in rat plasma by liquid chromatography–mass spectrometry and its application in pharmacokinetic study after oral administration of Folium Eriobotryae effective fraction

Folium Eriobotryae effective fraction (FEA), the extract of Folium Eriobotryae, had been used as anti‐hyperglycemia and anti‐hyperlipemia medicine in China. A previous study indicated that euscaphic acid, maslinic acid, corosolic acid, oleanolic acid and ursolic acid, the five structurally similar triterpene acids (containing two groups of structural isomers), are the major components of FEA. In the present study, we developed a specific and reliable LC‐MS method for simultaneous determination of the five triterpene acids in rat plasma, and further investigated their pharmacokinetic properties after oral administration of FEA. Following a simple sample preparation, chromatographic separation was achieved on a C₁₈ column with a mobile phase composed of methanol–0.1% ammonium acetate (80:20, v/v). Quantification was achieved by monitoring the selected ions at m/z 487.6 for euscaphic acid, m/z 471.5 for maslinic acid and corosolic acid, m/z 455.5 for oleanolic acid and ursolic acid and m/z 469.5 for internal standard. The method was validated to be specific, accurate and precise over the concentration ranges of 10–3000 ng/mL with limits of detections of 5 ng/mL for the five triterpene acids. Finally, the method was successfully applied to the pharmacokinetic study of the five structurally similar triterpene acids in rats after oral administration of FEA. Copyright © 2015 John Wiley & Sons, Ltd.     

Trans-esterification of fatty acids from microorganisms and human blood serum by trimethylsulfonium hydroxide (TMSH) for GC analysis

Summary Trimethylsulfonium hydroxide (TMSH) can convert fatty acids into the corresponding fatty acid methyl esters (FAMEs) in a single step. These fatty acids may also be bound in biomolecules such as phospholipids and/or glycerides. Complex mixtures of saturated and unsaturated FAMEs which may contain hydroxy and cylopropyl groups are obtained by trans-esterification; they can easily be separated in most cases by capillary GC. When FAMEs are generated from different microorganisms e.g. bacteria the patterns of the chromatograms are characteristic. Examples of characteristic patterns of bacteria with different cell wall structures are shown. The described method of transesterification can also be applied directly to blood serum without sophisticated sample pretreatment. The profiles of the chromatograms match well those described in the literature obtained by other methods of trans-esterification or sample preparation.     

Prebiotic Cell Membranes that Survive Extreme Environmental Pressure Conditions

Attractive candidates for compartmentalizing prebiotic cells are membranes comprised of single‐chain fatty acids. It is generally believed that life may have originated in the depth of the protoocean, that is, under high hydrostatic pressure conditions, but the structure and physical–chemical properties of prebiotic membranes under such conditions have not yet been explored. We report the temperature‐ and pressure‐dependent properties of membranes composed of prebiotically highly‐plausible lipids and demonstrate that prebiotic membranes could not only withstand extreme temperatures, but also serve as robust models of protocells operating in extreme pressure environments. We show that pressure not only increases the stability of vesicular systems but also limits their flexibility and permeability to solutes, while still keeping the membrane in an overall fluid‐like and thus functional state.     

Determination of fatty acid methyl esters derived from algae Scenedesmus dimorphus biomass by GC–MS with one‐step esterification of free fatty acids and transesterification of glycerolipids

Algae can synthesize, accumulate and store large amounts of lipids in its cells, which holds immense potential as a renewable source of biodiesel. In this work, we have developed and validated a GC–MS method for quantitation of fatty acids and glycerolipids in forms of fatty acid methyl esters derived from algae biomass. Algae Scenedesmus dimorphus dry mass was pulverized by mortar and pestle, then extracted by the modified Folch method and fractionated into free fatty acids and glycerolipids on aminopropyl solid‐phase extraction cartridges. Fatty acid methyl esters were produced by an optimized one‐step esterification of fatty acids and transesterification of glycerolipids with boron trichloride/methanol. The matrix effect, recoveries and stability of fatty acids and glycerolipids in algal matrix were first evaluated by spiking stable isotopes of pentadecanoic‐2,2‐d₂ acid and glyceryl tri(hexadecanoate‐2,2‐d₂) as surrogate analytes and tridecanoic‐2,2‐d₂ acid as internal standard into algal matrix prior to sample extraction. Later, the method was validated in terms of lower limits of quantitation, linear calibration ranges, intra‐ and inter‐assay precision and accuracy using tridecanoic‐2,2‐d₂ acid as internal standard. The method developed has been applied to the quantitation of fatty acid methyl esters from free fatty acid and glycerolipid fractions of algae Scenedesmus dimorphus .     

基于酶催化反应的核酸定量新方法

近年来 ,将染料自缔合或诱导缔合用于核酸定量测定备受关注 [1～ 3 ] .但是将酶与染料的缔合用于核酸定量测定尚未见报道 .氯化血红素 (hemin)可作为辣根过氧化物酶 (HRP)的模拟酶 ,能催化 H2 O2氧化对 -羟基苯乙酸 (p- HPA)生成荧光产物——联二对 -羟基苯乙酸的反应 [4 ,5] .由于 hemin在碱性介质中是阴离子化合物 ,能与阳离子化合物如阿尔新蓝 (Alcian Blue 8GX)发生缔合作用 ,从而使自身的催化性质被抑制 .当加入带负电荷的脱氧核糖核酸 (DNA)时 ,由于阿尔新蓝与 DNA的强烈作用使hemin与阿尔新蓝的缔合物被破坏 ,hemin的催化活…     

Quantification of fatty acids in erythrocytes and plasma by fast gas chromatography

As a result of the heterogeneous nature of lipid classes in complex biological matrices such as plasma and erythrocytes, it is imperative to have a robust and validated methodology for fatty acid quantification. The effective method presented here combines available methodology of fast gas chromatography and an improvement of the sample preparation methodology before injection into the gas chromatograph. This methodology ensures complete transesterification and quantification of total and individual fatty acids (and not only in relative amounts) by addition of internal standards. We considered sample preparation key, and we established the use of lysis buffer and ethanol for erythrocytes and plasma sample preparation, respectively. Fatty acid profile was determined by acid methylation and fast gas chromatography equipped with a flame ionization detector. The triacylglycerol 13:0, phosphatidylcholine 23:0, and methyl esters 21:0 were used as internal standards. Within the linearity of the calibration, the ratio of the peak area of each fatty acid over the peak area of the internal standard was constant (coefficient of variation ≤ 2.5). Satisfactory repeatability <15% and intermediate reproducibility < 15% were observed. Finally, this validated method was applied to a pre‐clinical trial that investigated the impact of dietary fats on accretion of specific fatty acids in plasma and erythrocytes.     

Simultaneous quantitation of seven pyrethroid metabolites in human urine by capillary gas chromatography–mass spectrometry

Pyrethroid insecticides are applied in the residential environment, as well as in agricultural crops, for insect control purpose. We developed and validated an accurate, sensitive, and reproducible analytical method to simultaneously detect seven pyrethroid metabolites, namely, 3‐(2,2‐dichlorovinyl)‐2,2‐dimethyl‐(1‐cyclopropane) carboxylic acid, 3‐(2,2‐dibromovinyl)‐2,2‐dimethyl‐(1‐cyclopropane) carboxylic acid, 3‐phenoxybenzoic acid, 4‐fluoro‐3‐phenoxybenzoic acid, 2‐methyl‐3‐phenylbenzoic acid, 4‐chloro‐α‐isoproply benzeneacetic acid, and 3‐(2‐chloro‐3,3,3‐trifluoroprop‐1‐enyl)‐2,2‐dimethylcyclopropanecarboxylic acid, in human urine. This method employs deconjugation with enzyme, SPE using Agilent C18 cartridges on a RapidTrace SPE workstation, derivatization using hexafluoro isopropanol and N,N′‐diisopropylcarbodiimide, and compounds separation and identification on GC–MS. The detection limits of seven metabolites were 0.02–0.08 ng/mL in urine. The recoveries of seven metabolites were 81–104%, 85–99%, and 83–99% in urine specimens fortified at 0.1, 0.4, and 3.2 ng/mL concentrations, respectively. The overall coefficient of variation was 4.3–10.8% in two quality control specimens which were repeatedly measured during a period of 2 months. This method was applied to urine samples collected from children living in Boston, MA. The median concentrations of six detected pyrethroid metabolites ranged from 0.06 to 0.86 ng/mL in urine.