Analysis of phytosterols and phytostanols in enriched dairy products by Fast gas chromatography with mass spectrometry

A Fast gas chromatography and mass spectrometry method for plant sterols/stanols analysis was developed, using a short capillary gas chromatography column (10 m × 0.1 mm internal diameter × 0.1 μm film thickness) coated with 5% diphenyl‐polysiloxane. A silylated mixture of the main plant sterols/stanols standards (β‐sitosterol, campesterol, stigmasterol, campestanol, sitostanol) was well separated in 1.5 min, with a good peak resolution (>1.4, determined on a critical chromatographic peak pair (β‐sitosterol and sitostanol)), repeatability (<13%), and sensitivity (<0.017 ng/mL). The suitability of this Fast chromatography method was tested on plant sterols/stanols‐enriched dairy products (yogurt and milk), which were subjected to lipid extraction, cold saponification, and silylation prior to injection. The analytical performance (sensitivity < 0.256 ng/mL and repeatability < 10.36%) and significant reduction of the analysis time and consumables demonstrate that Fast gas chromatography‐mass spectrometry method could be also employed for the plant sterols/stanols analysis in functional dairy products.     

基于脂肪酸差异的肉制品中猪源性成分鉴别方法的研究

建立了肉制品中脂肪酸的分析检测技术,通过分析脂肪酸含量、种类以及片段特征指纹图谱,实现了基于脂肪酸差异的肉制品中猪源性成分的鉴别。采用气相色谱法测定了大量肉制品,利用保留时间和质谱鉴定了36种脂肪酸成分,选取较为稳定的18种脂肪酸数据进行统计分析,确定不同油脂脂肪酸的差异,结合特征图谱,最终确定可用于鉴别猪源性成分的8种脂肪酸。该方法可用于确定肉制品中是否含有猪源性成分,方法简单、快速、成本低,辨别度较高,在猪源性成分鉴别中具有一定的应用前景。     

Trace analysis of surfactants derived from fatty alcohols II. Hydrolysis and enrichment techniques

Summary Acid catalyzed hydrolysis of fatty alcohol sulfates under reflux condition or by microwave heating is compared. Microwave hydrolysis turned out to be faster and more convenient to use. The combination of reflux hydrolysis of fatty alcohol sulfates or alkyl polyglycosides and the simultaneous steam distillation of the generated fatty alcohols gives a very powerful sample preparation and enrichment method for fatty alcohol sulfates and alkyl polyglycosides. The preconcentrated fatty alcohols are derivatized and detected via fluorescence detection. The applicability of the method is demonstrated by the analysis of fatty alcohol sulfates in cosmetics and in river water as matrices spiked with approximately 4 ppb fatty alcohol sulfates.     

气相色谱法在生物柴油生产工艺研究中的应用

综述了气相色谱法在生物柴油生产工艺研究中的应用,包括反应产物和生物柴油产品中脂肪酸甲酯含量和分布的测定,单脂肪酸甘油酯、二脂肪酸甘油酯和三脂肪酸甘油酯含量的测定,游离脂肪酸含量的测定以及微量甲醇含量的测定等。讨论了进样方式、色谱柱类型、硅烷化等因素对反应产物组成测定的影响;提出了一种采用双柱压力反吹的方式测定生物柴油产品中微量甲醇含量的方法：采用正丙醇作内标,甲醇与内标通过预切柱进入分析柱后,通过压力变化,将其余组分通过分流出口反吹出色谱系统;采用极性聚乙二醇色谱柱测定了8种不同植物油中脂肪酸甲酯的含量和分布。     

Paired-ion reversed-phase high-performance liquid chromatography of phenol sulfates in synthetic mixtures, algal extracts and urine

Phenol sulfate esters have been analyzed by paired-ion reversed-phase high-performance liquid chromatography. The method provided direct, rapid chromatography of phenol sulfates in crude extracts of the red alga (Polysiphonia lanosa (2,3-dibromo-4,5-dihydroxybenzyl alcohol 1',4-disulfate), of the brown alga Ascophyllum nodosum (1,2,3,5-tetrahydroxybenzene 2,5-disulfate), and in rat urine (resorcinol mono- and disulfates). Detector response (254 nm) was linear within the approximate range from 30--125 ng to 5--10 microgram. Semipreparative scale chromatography provided sufficient amounts of purified phenol sulfates for further analysis by paper electrophoresis.     

Analysis of special surfactants by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry

Multidimensional gas-chromatographic analyses of olesochemically based nonionic, anionic and several cationic surfactants in industrial cleaners are demonstrated. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry allows the simultaneous determination of fatty alcohols, fatty alcohol sulphates and alkyl polyglucosides. In addition, the determination of fatty alcohol ethoxylates up to C₁₀EO₈ (highest degree of ethoxylation) and C₁₈EO₅ (longest C-chain at an ethoxylation degree of five) and the analysis of fatty alcohol alkoxylates that contain ethoxy (EO) and propoxy (PO) groups could be realized. Because of decomposition in the injector and a weak EI-fragmentation, cationic surfactants such as alkyl benzyl dimethyl ammonium chloride could also be identified by their characteristic fragments. Thermogravimetric analyses confirmed that the temperature in a normal GC injector is not high enough to cause thermal decomposition of esterquats. However, we could demonstrate that a modified silylation procedure forms decomposition products of esterquats in the GC injector which are detectable by GC × GC–(TOF)MS and allows the identification of such GC-atypical analytes.     

Combination of chemical and electron-impact ionisation with GC×GC–qMS for characterization of fatty alcohol alkoxylate polymers in the low-molecular-weight range up to 700 Da

The class of fatty alcohol alkoxylates describes surfactants that are synthesised by reaction of fatty alcohols with alkoxides such as ethylene oxide or propylene oxide or a combination of both as copolymers. Such alkoxylates are used, for example, as nonionic surfactants in home and industrial cleaning and washing agents. Chemical characteristics of such alkoxylate copolymers, for example the degree of alkoxylation, the arrangement of building blocks (random or block polymerisation), the type of the starter, and endcapping, play an important role in application behaviour. The analysis of these characteristics is challenging because in many cases such copolymers have high polydispersity and a large number of constitutional isomers depending on the degree of alkoxylation. Furthermore, the alkoxylates often occur in a complex multicomponent matrix. Here we present a method for characterization of silylated fatty alcohol alkoxylates in the low-molecular-weight range by means of comprehensive two-dimensional gas chromatography–mass spectrometry with electron impact and chemical ionisation. This method also enables detailed analysis of the alkoxylates in a complex matrix such as modern detergents.     

Comparison of cholesterol oxidation product preparation methods for subsequent gas chromatographic analysis

An evaluation was made of the stability of cholesterol hydroperoxides (CHPs) under the analytical conditions and preparation methods commonly used for determination and quantification of cholesterol oxidation products (COPs). CHPs were prepared by photoxidation and separated by silica thin-layer chromatography. CHPs were individually collected by normal-phase liquid chromatography and then subjected either to reduction or to cold saponification. The corresponding hydroxyl derivatives were generated by reduction, whereas cold saponification gave rise predominantly to 7-ketocholesterol. In another test, silylated and non-silylated CHPs were separately injected into a gas chromatograph at 310 degrees C, collected, and re-injected into a gas chromatography-mass spectrometry system. The silylated CHPs were more stable than the non-silylated ones, giving 7-ketocholesterol, 7alpha- and 7beta-hydroxycholesterol as main degradation products. Two unknown degradation peaks were detected in both silylated and nonsilylated CHPs, having 384 as main m/z fragment. The study of their mass spectra led to the conclusion that peaks A and B correspond to 6alpha- and 6beta-hydroxycholesterol, respectively.     

Assay of lipids in dog myocardium using capillary gas chromatography and derivatization with boron trifluoride and methanol

The fatty acids of three lipid classes (free fatty acids, triglycerides, and cholesteryl esters) from dog heart were analysed by gas chromatography. Samples of the left ventricle were homogenized and total lipids were extracted. After separation by thin-layer chromatography, the bands of the lipid classes studied were scraped off, transmethylated according to the boron trifluoride-methanol procedure, and the fatty acid methyl esters were extracted and analysed. The problems related to the quantitation of fatty acids were investigated, namely transmethylation procedure, thin-layer chromatography, and gas chromatographic conditions. Fatty acid methyl esters were separated on capillary columns coated in the laboratory with SP 2340 stationary phase. The high performance of the separation ensured the reliability and the precision of the analysis.     

Analysis of deprotonated acids with silicon nanoparticle-assisted laser desorption/ ionization mass spectrometry

Chemically modified silicon nanoparticles were applied for the laser desorption/negative ionization of small acids. A series of substituted sulfonic acids and fatty acids was studied. Compared to desorption ionization on porous silicon (DIOS) and other matrix-less laser desorption/ionization techniques, silicon nanoparticle-assisted laser desorption/ionization (SPALDI) mass spectrometry allows for the analysis of acids in the negative ion mode without the observation of multimers or cation adducts. Using SPALDI, detection limits of many acids reached levels down to 50 pmol/μl. SPALDI of fatty acids with unmodified silicon nanoparticles was compared to SPALDI using the fluoroalkyl silylated silicon powder, with the unmodified particles showing better sensitivity for fatty acids, but with more low-mass background due to impurities and surfactants in the untreated silicon powder. The fatty acids exhibited a size-dependent response in both SPALDI and unmodified SPALDI, showing a signal intensity increase with the chain length of the fatty acids (C12-C18), leveling off at chain lengths of C18-C22. The size effect may be due to the crystallization of long chain fatty acids on the silicon. This hypothesis was further explored and supported by SPALDI of several, similar sized, unsaturated fatty acids with various crystallinities. Fatty acids in milk lipids and tick nymph samples were directly detected and their concentration ratios were determined by SPALDI mass spectrometry without complicated and time-consuming purification and esterification required in the traditional analysis of fatty acids by gas chromatography (GC). These results suggest that SPALDI mass spectrometry has the potential application in fast screening for small acids in crude samples with minimal sample preparation.     

微蒸馏气相色谱法测定水中低级脂肪醇的研究

考察了微蒸馏气相色谱法测定水样中多种低级脂肪醇的可行性。利用微蒸馏技术将水中的醇分离富集,用程序升温气相色谱法测定。正丙醇、异丙醇、正丁醇、异丁醇、正戊醇、异戊醇的浓缩倍数分别为169．3,137．6,197．4,149．2,142．7,126．0。检出限分别为0．021,0．031,0．032,0．032,0．066,0．065mg／L。样品中所存在组分的平均回收率分别为甲醇82．60％,正丙醇93．25％,正丁醇94．88％;相对标准偏差分别为甲醇7．7％,正丙醇4．7％,正丁醇3．4％。方法适用于水中多种微量低级醇的同时分析。     

Determination of ethyl glucuronide and fatty acid ethyl esters in hair samples

Hair testing for alcohol biomarkers is an important tool for monitoring alcohol consumption. We propose two methods for assessing alcohol exposure through combined analysis of ethyl glucuronide (EtG) and fatty acid ethyl esters (FAEEs) species (ethyl myristate, palmitate, stearate and oleate) in hair (30 mg). EtG was analysed by liquid chromatography–tandem mass spectrometry, while FAEEs were analysed by gas chromatography–tandem mass spectrometry using electron impact ionization. Both methods were validated according to internationally accepted guidelines. Linearity was proven between 3 and 500 pg/mg for EtG and 30–5000 pg/mg for FAEEs, and the limits of quantification were 3 pg/mg for EtG and 30 pg/mg for each of the four FAEEs. Precision and accuracy were considered adequate, processed EtG samples were found to be stable for up to 96 h left in the injector and processed FAEEs samples for up to 24 h. Matrix effects were not significant. Both methods were applied to the analysis of 15 authentic samples, using the cut‐off values proposed by the Society of Hair Testing for interpretation. The results agreed well with the self‐reported alcohol consumption in most cases, and demonstrated the suitability of the methods to be applied in routine analysis of alcohol biomarkers, allowing monitoring consumption using low sample amounts.     

全二维气相色谱-飞行时间质谱联用技术分析重馏分油中芳烃组成

通过对升温速度、二维补偿温度、调制周期等关键实验参数的优化,建立了全二维气相色谱-飞行时间质谱(GC×GC-TOF MS)分析重馏分油中芳烃组分的方法,得到了重馏分油芳烃组分按环数分布的二维点阵图。根据谱库检索、标准化合物对照及文献报道,对重馏分油芳烃组分中菲、甲基菲及芘、苯并蒽等常见多环芳烃(PAH)进行了准确定性,并将该方法应用到重馏分油加氢处理工艺研究中,对菲、芘的加氢处理产物进行了定性分析。该研究为重馏分油芳烃组分的准确定性提供了新的技术手段,为加深对油品加氢规律的认识提供了技术支持。全二维气相色谱与普通一维色谱对比,在重馏分油的芳烃组分分析上体现了极大优势。     

Simple off-line flash pyrolysis procedure with in situ silylation for the analysis of hydroxybenzenes in humic acids and coals

A simple device consisting of a glass pyrolysis chamber fitted for a commercial resistively heated pyrolysis probe and connected to a solvent desorption tube for air monitoring was applied to off-line pyrolysis under silylating conditions of humic acids (soil, lake) and coals. Samples were flash pyrolysed at 700 degrees C in the presence of excess hexamethyldisilazane, and evolved products were swept off by a nitrogen stream and trapped onto a charcoal filter from where they were desorbed with dichloromethane and analysed by gas chromatography (GC)-mass spectrometry. Humic acids afforded trimethylsilyl (TMS) ethers of phenols, 2-methoxyphenols (guaiacols), 2,6-dimethoxyphenols (syringols), and dihydroxy and trihydroxybenzenes as major products. TMSoxy benzenes were the principal products observed from pyrolysis/silylation of coals. In comparison with conventional pyrolysis, the in-situ derivatisation process enhances the levels of phenols with respect to hydrocarbons and improves the GC separation of isomers (e.g. meta- from para-cresol). With respect to tetramethylammonium hydroxide thermochemolysis, pyrolysis/silylation operates under milder conditions and permits discrimination between free and methylated hydroxy groups. The performance of the method for the quantitative determination of evolved product is described. Yields of evolved silylated mono and dihydroxybenzenes occur in the mg/g range with relative standard deviations generally between 16 and 30%.     

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.     

Formation of cyclic enol ethers from a labile biological precursor: an example of analytical artifacts

Three isomeric enol ethers are among those constituents apparently unique to mouse urine as identified by gas chromatographic analysis. These compounds appear to be artifacts arising from the cyclization and dehydration of 6-hydroxy-6-methyl-3-heptanone. Identification of the trimethylsilyl ether of 6-hydroxy-6-methyl-3-heptanone in the silylated ether extract of mouse urine indicates that the precursor keto alcohol is indeed present in the urine. Since similar heterocyclic compounds are often identified in urine samples analyzed by gas chromatography, formation of various analysis artifacts arising from analogous cyclization and dehydration reactions is likely.     

Simple gas chromatographic method for the determination of medicagenic acid in alfalfa (Medicago sativa)

A gas chromatographic method for the determination of medicagenic acid in alfalfa leaves, stems, entire plant (tops) and roots and also in leaf protein concentrates is described. The method is based on extraction of lucerne saponins followed by hydrolysis of the triterpene glycosides. After derivatization of the liberated sapogenins to silylated products, the trimethylsilylated medicagenic acid was determined by gas chromatography. The sensitivity of the method permits the detection of 50 ng of medicagenic acid.     

Ion trap mass spectrometry of trimethylsilylamides following gas chromatography

Fatty acid amides are a class of compounds with newly discovered biological activity. The ion trap mass spectrometric characteristics of silylated fatty acid amides were examined. Silylation of primary fatty acid amides is required prior to gas chromatography owing to thermal instability of the underivatized compound. The trimethylsilylated amides do not yield a molecular ion under normal electron ionization conditions (70 eV). With methane as a chemical ionization gas, the [M+H]+ ion appears. The [M+H]+ ion also appears when the helium buffer gas pressure is increased in the ion trap. There are three fragments other than the [M+H]+ peak that are predominant in the ion trap mass spectra of these compounds. Two of the fragments have been reported previously, namely the m/z 59 and the [M-71]+ fragments. The fragment of m/z 72 was identified and is the result of a rearrangement. Isotopic labeling was used to confirm fragment identity and the composition of the rearrangement products. Fragmentation patterns were affected by the amide chain length and concentration.     

Cinnamyl alcohols and methyl esters of fatty acids from Wedelia prostrata callus cultures

Two methyl esters of fatty acids, namely octadecanoic acid methyl ester (methyl stearate) and hexadecanoic acid methyl ester (methyl palmitate), in addition to four cinnamyl alcohol derivatives, sinapyl alcohol, coniferyl alcohol, p-coumaryl alcohol and coniferyl alcohol 4-O-glucoside (coniferin), were isolated from callus cultures of Wedelia prostrata. The structure of coniferin was established by spectroscopic and chemical methods, while the other compounds were identified by gas chromatography-mass spectrometry and thin layer chromatography in comparison with standards.     

High temperature gas chromatography of trimethylsilyl derivatives of alcohol ethoxylates and ethoxysulfates

Conversion of ethoxylated alcohols to trimethylsilyl derivatives and subsequent high temperature gas chromatography allowed for the determination of alkyl chain distribution, mole average degree of ethoxylation and weight percent distribution of several commercial mixtures. Repetitive derivatizations and analyses of a mixture with a vendor specified mole average degree of ethoxylation of 3.0 (Neodol 23-3), yielded an experimental result of 2.93 ± 0.05 (n = 6). Mixtures with different alkyl chain distributions and higher degrees of ethoxylation provided similar accuracy. Extension of the method to the analysis of ethoxylated alcohol sulfate raw materials and ethoxylated alcohol sulfates in dishwashing liquids is discussed.