Isomeric composition of the ester fraction from epicuticular waxes of Festuca arundinacea Schreb

The ester portion of epicuticular waxes of tall fescue (Festuca arundinacea Schreb.) is composed of mixtures of homologous series of fatty acids esterfied with fatty alcohols. GC analyses of natural esters gave rise to the separation of several compounds of different chain length. To identify and quantify individual components in the mixture, GC/MS analyses were carried out, and the mass spectra of each peak were recorded and analyzed for characteristic ions. This approach permitted a comparison with data obtained from classical methods using GC analysis of acid and alcohol moieties obtained by hydrolysis.     

GC-MS investigation of α-polyfluoroalkylbenzyl phosphorus esters

The stereochemistry of some α-polyfluoroalkylbenzyl phosphorus esters has been studied by capillary gas chromatography (CGC). The compounds are mixtures of two or three diastereomers, depending on the number of asymmetric centers and the molecular symmetry. The primary fragmentation processes in the mass spectra of the phosphorus esters and their deuterated analogous have also been studied.     

Identification of 19 phthalic acid esters in dairy products by gas chromatography with mass spectrometry

A detection method for 19 kinds of phthalic acid ester compounds analyzed by n‐hexane/ether/acetonitrile 1:7:8 v/v/v mixed solvent extraction, quick, easy, cheap, effective, rugged, and safe purification and internal standard method of quantitative gas chromatography with mass spectrometry was established. This method can effectively remove interfering materials, such as lipids, fatty acids, and pigments, from dairy products. The 19 kinds of phthalic acid ester compounds were within a 0.025–0.2 mg/kg range, the recovery rate was 65.2–125.7%, relative standard deviation was 7.9–15.4% (n = 6), and the limit of detection was 0.005–0.02 mg/kg. Concentrations of the 19 kinds of phthalic acid ester compounds ranged between 0.01 and 0.12 mg/kg in ten dairy materials and 20 dairy products. The established method is simple, rapid, accurate, and highly sensitive.     

Discovery of mass spectral characteristics and automatic identification of wax esters from gas chromatography mass spectrometry data

The mass spectral characteristics of wax esters were systemically summarized and interpreted through data mining of their standard mass spectra taken from NIST standard mass spectral library. Combining with the rules of retention indices described in the previous study, an automatic system was subsequently developed to identify the structural information for wax esters from GC/MS data. After tested and illustrated by both simulated and real GC/MS data, the results indicate that this system could identify wax esters except the polyunsaturated ones and the mass spectral characteristics are useful and effective information for identification of wax esters.     

Esterification of aliphatic hydroxy acids to n-butyl esters in aqueous solutions for their gas chromatographic analysis

Summary Aliphatic hydroxy acids were esterified in aqueous solution in the presence of sulfuric acid. Esterification of lactic, tartronic malic and citric acids in water/n-butanol mixtures with mole ratios between 0.02 and 2.53 can be utilized for the determination of these aliphatic hydroxy acids by gas chromatography. Water does not interfere at water/n-butanol mole ratios below 0.02. For mole ratios above 0.02 anhydrous sodium sulfate is used for the binding of water. The mole ratio range was 0.25–2.53 for anhydrous sodium sulfate/water, and 0.32–1.27 for sulfuric acid/anhydrous sodium sulfate.     

Esterification of aliphatic hydroxy acids to n-propyl esters in aqueous solutions for their gas chromatographic analysis

Summary Aliphatic hydroxy acids were esterified in aqueous solution in the presence of different amounts of sulfuric acid. Esterification of lactic, tartronic, malic and citric acids in water/n-propanol mixtures with mole ratios between 0.03 and 2.15 can be utilized for the determination of these acids by gas chromatography. Water does not interfere at water/n-propanol mole ratios below 0.03. For mole ratios above 0.03 anhydrous sodium sulfate is used for the binding of water. The mole ratio range was 0.24–2.13 for anhydrous sodium sulfate/water, and 0.16–1.28 for sulfuric acid/anhydrous sodium sulfate.     

Accurate determination of the degree of substitution of long chain cellulose esters

The determination of the degree of substitution (DS) of fatty acid cellulose esters with alkyl chain lengths from C8 to C18 was performed by direct transesterification with trimethylsulphonium hydroxide (TMSH) using tert-butyl methyl ether (MTBE) as a solvent. Transesterification was demonstrated to be quantitative at 75 °C in 60 min. The quantification of the formed fatty acid methyl esters was performed by gas chromatography (GC). After the optimization of the method, long chain cellulose esters (LCCE) could be analyzed in a wide range of DS. The obtained values were compared to those given by other existing protocols. LCCE with DS-values in a range of 5 × 10⁻⁵ to 3 were analyzed with high accuracy. Reproducibility is weakened for high DS values if the sample has a compact aspect limiting the accessibility of TMSH to the ester functions. This method can also be suitable for the analysis of mixed cellulose esters.     

胶束扫集毛细管电动色谱法测定药物中3种邻苯二甲酸酯

采用胶束扫集毛细管电动色谱技术,建立了测定药物中邻苯二甲酸二甲酯(DMP)、邻苯二甲酸二乙酯(DZP)和邻苯二甲酸二丁酯(DBP)的方法。电泳缓冲体系含80 mmol/L SDS,20 mmol/L NaH2PO4(pH 2.20),5%甲醇(V/V),分离电压-18 kV,重力进样80s×15.0cm,检测波长225 nm,使用Φ50μm×62.0 cm石英毛细管,有效长度50.0 cm。讨论了磷酸盐浓度、有机改善剂、SDS浓度、分离电压、进样时间等因素的影响,并考察了胶束扫集法对DMP、DEP和DBP的富集能力。在优化条件下,线性关系良好,相关系数大于0.9986,DMP、DEP和DBP的线性范围分别为1.25～240,1.04～200和1.56～200 mg/L,检出限分别为0.26,0.26和0.39 mg/L。方法应用于肠溶片中DMP、DEP和DBP的测定,回收率在93.3%～108%之间,RSD≤5.2%。每次样品测定可在10 min内完成。     

Use of 2,2-dimethoxypropane for the direct gas chromatographic-mass spectrometric determination of some organic compounds in water

The well known reaction between 2,2-dimethoxypropane and water allows for the conversion of an aqueous into an organic solution ready to be injected directly into a gas chromatographic-mass spectrometric (GC-MS) system. Only time, temperature and water/ketal ratio were the parameters studied among those which influence the equilibrium reaction. The reaction environment is not suitable for all compounds: acids, esters, alcohols, amines, ketones and phenols may react with methanol, acetone and ketal owing to Amberlyst being present as catalyst. This method is proposed for the GC-MS analysis of aqueous solutions containing hydrocarbons, halogenated hydrocarbons and ethers. The determination of some pesticides in water is reported.     

Analysis of functionalized polyisobutylenes by capillary SFC, SEC, HPLC, and CGC-MS after fraction collection

Summary An analytical strategy has been developed for analysis of polyisobutylenes partially functionalized with isothiocyanate groups ( ) by capillary supercritical-fluid chromatography (CSFC), size- exclusion chromatography (SEC), and reversed-phase liquid chromatography (RPLC). Fractions collected from semi-preparative RPLC and SEC were further characterized by capillary GC-MS (gas chromatography coupled with mass spectrometry). Complete characterization of the polymer was achieved by comparing the results obtained from the different techniques. The degree of polymerization and the relative quantity of the different series of macromolecular chains of polyisobutylene were estimated.     

Liquid-liquid biphasic synthesis of long chain wax esters using the Lewis acidic ionic liquid choline chloride·2ZnCl2

The first liquid-liquid biphasic synthesis of wax esters in a Lewis acidic ionic liquid, choline chloride·2ZnCl₂ by the esterification of long chain carboxylic acids with long chain alcohols is described. The reported reaction system has the advantages of both homogeneous and heterogeneous catalysis with high product yield and the ease of product as well as catalyst separation without the use of an organic solvent. The ionic liquid studied plays the dual role of solvent as well as catalyst and is recycled up to six times without any significant loss of activity.     

Simultaneous determination of trace migration of phthalate esters in honey and royal jelly by GC–MS

A simple, rapid, and reliable liquid–liquid extraction coupled to GC–MS method was developed and validated for the quantification of 22 phthalate esters (PAEs) in honey and royal jelly. Instrument parameters for GC–MS were tested to obtain the satisfactory separation between 22 PAEs with high sensitivity. The extraction procedure was optimized in order to achieve the best recovery. The following criteria were used to validate the developed method: linearity, LOD, lower LOQ, precision, accuracy, matrix effect and carry‐over. Correlation coefficients were >0.999 by applying the linear regression model based on the least‐squares method with a weighting factor (1/x). The intra‐ and interday precision were within 12.7% in terms of RSD, and the accuracy was within ?11.8% in terms of relative error. The mean extraction recoveries ranged between 80.1 and 110.9% for honey and royal jelly. No significant matrix effect and carry‐over for PAEs were observed for the analysis of honey and royal jelly samples. A total of 20 real samples were analyzed for a mini‐survey using the developed method. Seven PAEs in honey samples and five PAEs in royal jelly samples were found, indicating potential contamination with several PAEs.     

Mass spectrometric profiling of saturated fatty acid esters of steroids separated by high-temperature gas chromatography

An efficient analytical method for simultaneous determination of 12 SFEs in serum is described. The method involves solid-phase extraction to isolate of SFEs from interfering species, especially cholesteryl esters, conversion to trimethylsilyl (TMS) ether derivatives for the direct analysis by gas chromatography–mass spectrometry (GC–MS) using a high temperature MXT-1 (Silcosteel-treated stainless steel) capillary column. All SFEs as their TMS derivatives were well separated with excellent peak shapes within 12 min. Overall recoveries ranged from 88% to 119%, with a detection limits for SFEs ranged from 2 to 30 μg L⁻¹. The linearity as correlation coefficient was higher than 0.99 except for pregnenolone-3-arachidate (r² = 0.98) in the concentration range of 5–3000 μg L⁻¹. Ten serum samples obtained from volunteers were also analyzed and quantitatively determined of DHEA-3-palmitate and pregnenolone-3-stearate in 1.8–1195.8 μg L⁻¹ concentration. The devised high temperature GC–MS method could be useful for identification of SFEs in biological specimens including serum.     

Matrix interference free determination of perchlorate in urine by ion association-ion chromatography-mass spectrometry

Quantitative measurement of perchlorate in biological fluids is of importance to assess its toxicity and to study its effects on the thyroid gland. Whenever possible, urine samples are preferred in toxicologic/epidemiologic studies because sample collection is non-invasive. We present here a pretreatment method for the determination of perchlorate in urine samples that lead to a clean matrix. Urine samples, spiked with isotopically labeled perchlorate, are exposed to UV to destroy/decompose organic molecules and then sequentially treated with an H⁺-form cation exchange resin to remove protolyzable compounds, with ammonia to raise the pH to 10-11 and finally passed through a mini-column of basic alumina to remove the color and other organic matter. After filtration through a 0.45 μm syringe filter, the sample thus prepared can be directly injected into an ion chromatograph (IC). We use ion association-electrospray ionization-mass spectrometry (ESI-MS) to detect and quantify perchlorate. The proposed sample preparation method leads to excellent limits of detection (LOD's) for perchlorate since there is essentially no dilution of sample and the matrix effects are eliminated. Results of urine samples from both men and women volunteers are reported for perchlorate, as well as for iodide and thiocyanate, which are generally present at much higher concentrations and for which a “dilute and shoot” approach is adequate. The limit of detection (S/N = 3) for iodide, thiocyanate and perchlorate by the present method was 0.40, 0.10 and 0.080 μg l⁻¹, respectively.     

On-line solid phase extraction coupled to capillary LC-ESI-MS for determination of fluoxetine in human blood plasma

An instrumental setup including on-line solid phased extraction coupled to capillary liquid chromatography-electrospray ionization-mass spectrometry (SPE-capLC-ESI-MS) has been constructed to improve the sensitivity for quantification of fluoxetine hydrochloride in human plasma. Prior to injection, 0.5 mL of plasma spiked with metronidazole (internal standard) was mixed with ammonium formate buffer for effective chloroform liquid-liquid extraction. The method was validated in the range 5-60 ng mL⁻¹ fluoxetine, yielding a correlation coefficient of 0.999 (r²). The within-assay and between-assay precisions were between (8.5 and 11%) and (6.6 and 7.5%), respectively. The method was used to determine the amount of fluoxetine in a healthy male 14 h after an intake of one capsule of the antidepressant and anorectic Flutin^®, which contains 20 mg fluoxetine per each capsule. Fluoxetine was detected, and the concentration was calculated to 9.0 ng mL⁻¹ plasma. In the preliminary experiments, conventional LC-UV instrumentation was employed. However, it was found that employing a capillary column with an inner diameter of (0.3 mm I.D. × 50 mm, Zorbax C₁₈) increased the sensitivity by a factor of ∼100, when injecting the same mass of analyte. Incorporating an easily automated C₁₈ reversed phase column switching system with SPE (1.0 mm I.D. × 5.0 mm, 5 μm) made it possible to inject up to 100 μL of solution, and the total analysis time was 5.5 min.     

Characterization of mixtures of biocidal oligoguanidines by capillary electrophoresis and high-performance liquid chromatography coupled to mass spectrometry

The polycondensation of guanidine hydrochloride and 2,2′-(ethylenedioxy)bis(ethylamine) leads to various types of oligomeric guanidines exhibiting a broad spectrum of biocidal activities. In the present work a reversed-phase high-performance liquid chromatographic method with a gradient consisting of aqueous 0.1% trifluoroacetic acid and acetonitrile as mobile phase has been developed to separate these oligoguanidines according to type and chain length. The combination with electrospray mass spectrometry allowed the identification of the various compounds. By this technique, some structures already suggested in the literature could be confirmed, and several additional oligoguanidines not yet reported could be identified. As a complementary technique, capillary zone electrophoresis was investigated. Best results were obtained with carrier electrolytes consisting of phosphoric acid in water/acetonitrile mixtures. Although the number of peaks that could be separated by the electrophoretic method was considerably lower than in case of the chromatographic method, capillary electrophoresis in combination with UV detection at 195 nm may still be a fast method suitable for quantitation of some of the major compounds and for monitoring the reaction rate during the polycondensation reaction.     

Derivatization of amines with chloroformate esters for gas chromatographic analysis

Summary The gas chromatographic analysis of amines after conversion to electron capture sensitive carbamates in two-phase systems has been studied. Hydrophilic compounds, for instance methylamine, are reacted with 2,2,2-trichloro-tert. butyl chloroformate. Quantitation below 10^–7 M can be made by thermionic or electron capture detection. A hydrophobic amine, namely N,N-dimethyl-n-octylamine, was derivatized with 2,4,6-tribromophenyl chloroformate with addition of iodide ion to the aqueous phase. The favorable effect of iodide ion as well as the choice of pH and chloroformate ester is discussed.Presented at the 14th International Symposium on Chromatography London, September, 1982