Direct methylation at the surface of Carbopack B Part II: Determination of phenoxyalkanoic acid herbicides

The determination of phenoxyalkanoic acids in different types of water within the limits of the European drinking water guideline is described. Most of these acids are used world-wide as herbicides and growth regulators. Compounds having an acidic hydrogen in their structure are very strongly adsorbed on Carbopack B, a special graphitized carbon black. This effect was used for the transformation of analytes to methyl esters directly on the surface of the adsorbent, using trimethylsulfonium hydroxide (TMSH) as derivatization reagent. After elution with ethyl acetate the derivatives were identified and quantified by gas chromatography/mass spectrometry (GC/MS). The interaction between analyte and adsorbent and the yields of the derivatization step are influenced by the length of the alkanoic chain. Received: 21 June 1999 / Revised: 23 August 1999 / Accepted: 24 August 1999     

Direct methylation at the surface of Carbopack B Part I: Determination of phenolic pesticides

 A procedure for the determination of phenolic pesticides, i.e. the hydroxybenzonitriles bromoxynil and ioxynil and the 2,4-dinitrophenol-derivatives dinoseb, dinosebacetate, dinoterb, dinoterbacetate, dinobuton, binapacryl and DNOC is presented. The herbicides with a free phenolic OH-group as well as the corresponding esters are very strongly adsorbed on Carbopack B, a special graphitized carbon black. In contrast to the esters, which can be removed almost quantitatively, the substances with a free phenolic OH-group cannot be eluted in any significant amount. This effect was used for the derivatization of the herbicides directly on Carbopack B, using diazomethane or TMSH as reagents. The derivatives were eluted with ethylacetate and identified and quantified by GC/MS. For recovery studies, water samples were spiked with the pesticides in concentrations within the range tolerated by the European Drinking Water Guideline. Received: 25 March 1996/Revised: 12 June 1996/Accepted: 17 June 1996     

A DDQ-promoted metal-free cross-coupling of 1,3-diarylpropynes with hydroxyl via Sp C-H bond activation to form C-O bond

A metal-free coupling reaction between 1,3-diarylpropynes and alcohols/phenols/acids via propargylic sp³ C-H bonds activation and C-O bond formation reaction promoted by DDQ was realized. The reaction afforded series of propargyl ethers, propargyl esters and propargyl ketals.     

Trimethylsulfonium hydroxide as derivatization reagent for the chemical investigation of drying oils in works of art by gas chromatography

A procedure for the determination of fatty acids (FA) and glycerol in oils has been developed. The method includes a derivatization step of the FAs into their methyl esters or a transesterification of the triacylglycerols with trimethylsulfonium hydroxide (TMSH), respectively. The analysis is carried out by gas chromatography with parallel flame ionization and mass spectrometric detection. The parameters involved in the transesterification reaction were optimized. Only the stoichiometric ratio of TMSH:total FA amount showed a significant influence on the reaction yield. Relative standard deviations for 10 replicates were below 3% for all FAs studied and their linearity range was 0.5-50 mmol/L, when using heptadecanoic acid as an internal standard. The final procedure was rapid and required little sample handling. It was then tested on fresh oil samples and presented satisfying results, in agreement with previous works.     

Reaction efficiency of organic alkalis with various classes of lipids during thermally assisted hydrolysis and methylation

Reaction efficiencies of two organic alkalis, tetramethylammonium hydroxide (TMAH) and trimethylsulfonium hydroxide (TMSH), with lipids during thermally assisted hydrolysis and methylation (THM) were examined focusing on (1) the types of lipids and (2) degree of unsaturation of fatty acid moieties. Different types of lipids such as triglycerides, phospholipids, free fatty acids and cholesteryl esters containing saturated, monounsaturated or polyunsaturated fatty acid (PUFA) residues were subjected to THM-gas chromatography (GC) in the presence of TMAH or TMSH. The obtained results revealed that the THM reaction using TMAH allowed almost quantitative methylation of saturated and monounsaturated fatty acid components independently of the classes of lipids. However, strong alkalinity of TMAH brought about isomerization and/or degradation of PUFA components. In contrast, the use of TMSH was effective to highly sensitive detection of PUFA as well as saturated and monounsaturated fatty acid components contained in triglycerides, phospholipids (phosphatidylcholines) and free fatty acids. On the other hand, TMSH was proved to react hardly with any kind of fatty acid residues in cholesteryl esters due to their steric hindrance.     

GC/MS determination of fatty acid picolinyl esters by direct curie-point pyrolysis of whole bacterial cells

A single-step method suitable for cellular fatty acid derivatization to picolinyl esters with the use of a pyrolyzer as a thermochemical micro-reactor was developed for whole bacterial cells. This reduced the preparation time from several hours to less than two minutes. In addition, the minimal bacterial mass required for analysis was reduced from several milligrams to micrograms. The profiling of cellular fatty acids of gram-positive and gram-negative bacteria was achieved using three derivatization methods: preparation of methyl esters, beta-picolinyl esters by Harvey's method and a new method based on pyrolytic derivatization to beta-picolinyl esters. It was shown that there are great similarities between profiles of bacterial fatty acids determined by the pyrolytic derivatization method and traditional preparation methods of picolinyl and methyl esters prior to GC analysis. Results obtained by application of the new technique have immense diagnostic value due to vast similarities between profiles of fatty acids derivatized to either picolinyl and methyl esters. Although the latter are referred to in the literature most often, mass spectra of picolinyl esters contain fragment ions that provide structural information about the chain branching, position of unsaturation, and other substituents.     

GC—MS analysis of carboxylic acids in petroleum after esterification with fluoroalcohols

The GC–MS characteristics of carboxylic acid esters prepared from fluorine-containing alcohols were compared to those of methyl esters. The GC retention of 2,2,2-trifluoroethyl (TFE) esters was less than, and 2,2,3,3,4,4,4-heptafluoro-1-butyl (HFB) esters was approximately equivalent to that of methyl esters. Mass spectra of TFE and HFB aliphatic esters show significantly more intense molecular and key fragment ions than those of methyl esters. Also, owing to their significantly higher molecular weights, TFE or HFB ester molecular ions and most fragment ions of interest occur at significantly higher m/z values than most potential interfering ions. Data for about 70 individual TFE and HFB esters are reported. Application of the methodology to a petroleum-derived carboxylic acid concentrate resulted in identification of straight chain, isoprenoid, methyl-substituted straight chain (2-, 3-, 5-,10-, 12-positions along chain), and dimethyl-substituted straight chain acids containing from 11 to 22 carbons. Benzoic acid and homologs with up to 3-carbons in alkyl substitutents were minor components in the sample. The procedure provided for forming TFE and HFB esters from free acids requires less time and effort than a previously reported method, while retaining its capability for achieving essentially quantitative conversion. Free hydroxyl groups in alcohols and phenols are converted to trifluoroacetate esters concurrently with formation of TFE/HFB carboxylic acid esters. The reaction products, including compounds with two functional groups (diacids, salicylic acid, etc.), chromatograph well on conventional nonpolar GC stationary phases.     

New possibilities of dimethylformamide dimethylacetal as a derivatization agent for gas chromatography/mass spectrometry analysis

It is shown that the use of dimethylformamide dimethylacetal for the derivatization of analytes in gas chromatography/mass spectrometry cannot be restricted by the known conversion of carboxylic acids, phenols, and thiols into their methyl esters (ethers), as well as by the conversion of non-volatile amino acids (and C-amino compounds of other classes) into their dimethylaminomethylene derivatives. The application of this reagent to the derivatization of hydrazine derivatives and volatile carbonyl-containing analytes is considered. In the last case, the reaction proceeds selectively via CH₂ and/or CH₃ groups in the α-position to the carbonyl fragment. The principal predestination of the derivatization of such analytes is their characterization by differences of gas-chromatographic retention indices (ΔRI) of reaction products and initial substrates. The ranges of variation of such increments, ΔRI, appeared to be different for different subgroups of carbonyl compounds; this allowed us to determine their structures more precisely. The mass spectra of C-dimethylaminomethylene derivatives of some carbonyl compounds, preferably 2-substituted 1-methyl- and 1-aryl-3-(dimethylamino) prop-2-en-1-ones, revealed intense [M–17] peaks. The appearance of these signals can be explained by the migration of a hydrogen atom and the formation of [М–ОН]⁺ ions.     

Automated Trimethyl Sulfonium Hydroxide Derivatization Method for High-Throughput Fatty Acid Profiling by Gas Chromatography–Mass Spectrometry

Fatty acid profiling on gas chromatography–mass spectrometry (GC–MS) platforms is typically performed offline by manually derivatizing and analyzing small batches of samples. A GC–MS system with a fully integrated robotic autosampler can significantly improve sample handling, standardize data collection, and reduce the total hands-on time required for sample analysis. In this study, we report an optimized high-throughput GC–MS-based methodology that utilizes trimethyl sulfonium hydroxide (TMSH) as a derivatization reagent to convert fatty acids into fatty acid methyl esters. An automated online derivatization method was developed, in which the robotic autosampler derivatizes each sample individually and injects it into the GC–MS system in a high-throughput manner. This study investigated the robustness of automated TMSH derivatization by comparing fatty acid standards and lipid extracts, derivatized manually in batches and online automatically from four biological matrices. Automated derivatization improved reproducibility in 19 of 33 fatty acid standards, with nearly half of the 33 confirmed fatty acids in biological samples demonstrating improved reproducibility when compared to manually derivatized samples. In summary, we show that the online TMSH-based derivatization methodology is ideal for high-throughput fatty acid analysis, allowing rapid and efficient fatty acid profiling, with reduced sample handling, faster data acquisition, and, ultimately, improved data reproducibility.     

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.     

Enantiomeric separation of alcohols and amines on a proline chiral stationary phase by gas chromatography

A new chiral stationary phase for gas chromatography was prepared by covalently attaching a diproline chiral selector that has proven to be effective in liquid chromatography to a methylhydrosiloxane-dimethylsiloxane copolymer. With this new chiral stationary phase for GC, racemic aromatic alcohols could be resolved without derivatization. Racemic aromatic and aliphatic amines could also be resolved after derivatization of the amino groups with trifluoroacetic anhydride or isopropyl isocyanate. On this stationary phase, the isopropyl isocyanate derivatives of amines showed higher enantioselectivity than the trifluoroacetic anhydride derivatives. In both the enantiomeric separations of alcohols and derivatized amines, the aromatic racemic analytes showed higher enantioselectivities than their aliphatic analogs. Some of the alpha-amino and alpha-hydroxy aromatic acids could also be separated after derivatization to N-trifluoroacetyl methyl esters for amino acids or O-trifluoroacetyl methyl esters for hydroxyl acids.     

Fast identification of mycobacterium species by GC analysis with trimethylsulfonium hydroxide (TMSH) for transesterification

Trimethylsulfonium hydroxide (TMSH) reproducibly converts fatty acids bound in, e.g., biomolecules such as phospholipids and/or glycerides, into the corresponding fatty acid methyl esters (FAMEs). The transesterification can be performed at room temperature in a fast single step reaction. Surprisingly, secondary alcohols and mycolic acid cleavage products (MACPs) are also released from mycobacteria under these conditions. The complex reaction mixtures containing FAMEs, MACPs, and secondary alcohols can easily be separated by high resolution temperature-programmed capillary GC. Different species of mycobacteria give rise to characteristic chromatographic patterns and the amount of lipids from a single colony of mycobacteria is sufficient for reliable identification of the bacteria. The profiles of the chromatograms match well those obtained from other sample preparation techniques. The TMSH method of identification of mycobacteria from the patterns of the gas chromatograms is faster and more sensitive than conventional methods, which also involve transesterification. The identification of mycobacterial species by microbiological culture techniques is difficult to perform and requires several weeks.     

Preparation of glycine-conjugated bile acids and their gas/liquid chromatographic analysis on an aluminum-clad flexible fused silica capillary column.

This paper describes a method for the direct gas/liquid chromatographic (GC) analysis of 46 glycine-conjugated bile acids, which differ from one another in the number, position and configuration of the hydroxyl groups at positions C-2, C-3, C-4, C-6, C-7 and/or C-12. Free bile acids were converted quantitatively on a micro scale to ethyl ester-trimethylsilyl (Et-TMS) and methyl ester-dimethylethylsilyl (Me-DMES) ether derivatives of the corresponding glycine conjugates. The Et-TMS and Me-DMES ethers of the glycine conjugates were chromatographed on an aluminum-clad flexible fused silica capillary column coated with a thin film (0.1 micron) of chemically bonded and cross-linked methylpolysiloxane. Relative retention time (RRT) and methylene unit (MU) values were determined for the 46 compounds and their GC behaviour was discussed. The derivatization procedure and the retention data would be useful for the direct GC identification of unknown glycine-conjugated bile acid mixtures extracted from biological samples.     

Extraction of polar and hydrophobic pollutants using accelerated solvent extraction (ASE)

Accelerated solvent extraction (ASE) shows higher recoveries for PAHs in comparison with traditional Soxhlet extraction, but in a fraction of time and with less solvent consumption. Better recoveries are especially achieved with PAHs of high reactivity, the latter being expressed by the structure-to-count ratio (SCR). To estimate polar pollutants including phenols/benzenediols, the sample was subjected to a combined in-situ derivatization/extraction approach using 2% v/v acetic anhydride in toluene. The main reason for the better recovery obtained in this way, in comparison with the classical ASE approach, is to overcome strong matrix-analyte interactions. Analogously, fatty acids were analyzed as methyl esters obtained by in-situ derivatization/extraction using boron trifluoride.     

Studies on steroids. CCXXVIII Trace analysis of bile acids by gas chromatography-mass spectrometry with negative ion chemical ionization detection

A suitable derivatization method for the trace analysis of bile acids by gas chromatography (GC) in combination with negative ion chemical ionization (NICI) mass spectrometry is described. Of various derivatives for the carboxyl group, the pentafluorobenzyl (PFB) ester provided the highest value of the ratio of the negative to the positive ion current. A characteristic carboxylate anion [M - 181]- was produced as the most abundant ion by the loss of the PFB group in NICI. The PFB esters were further derivatized to the dimethylethylsilyl (DMES) ethers, whereby lithocholic acid, deoxycholic acid, chenodeoxycholic acid, ursodeoxycholic acid and cholic acid were distinctly separated by GC on a cross-linked methyl silicone fused-silica capillary column. The detection limit for the PFB-DMES derivatives of dihydroxylated bile acids was 2 fg when the fragment ion was monitored at m/z 563 in the NICI mode using isobutane as a reagent gas.     

GC Analysis of Organic Acids and Phenols Using On-Line Methylation with Trimethylsulfonium Hydroxide and PTV Solvent Split Large Volume Injection

The combination of on-line methylation using trimethylsulfonium hydroxide with large volume injection of 100 μL was evaluated for the analysis of organic acids and phenols in water. Solvent split injection was applied with complete evaporation of the solvent before analytes were transferred onto the GC column. Despite complete solvent removal, losses were very low compared to conventional splitless injection even for volatile acidic compounds such as propionic acid and phenol. This is explained by intermediate formation of low volatility trimethylsulfonium salts of the analytes which were held in the injector for long evaporation times of up to 10 min, if the evaporation temperature was as low as 10°C. Using a simple liquid/liquid extraction procedure, volatile fatty acids, dicarboxylic acids, benzoic acids and phenols could be detected in 5 mL of water at concentrations of 0.04–0.1 μmol/L with GC/MS in full scan mode. Lactic, pyruvic, and also malonic acids could only be detected at higher levels because of their limited extractability from water as well as their poorer methylation yields. The method provides an easy way to sensitively detect acidic compounds of medium to high volatility in water. It was applied for screening of organic acids and phenols in batch cultures of anaerobic bacteria of which one example is shown.     

Extraction of polar and hydrophobic pollutants using accelerated solvent extraction (ASE)

Accelerated solvent extraction (ASE) shows higher recoveries for PAHs in comparison with traditional Soxhlet extraction, but in a fraction of time and with less solvent consumption. Better recoveries are especially achieved with PAHs of high reactivity, the latter being expressed by the structure-to-count ratio (SCR). To estimate polar pollutants including phenols/benzenediols, the sample was subjected to a combined in-situ derivatization/extraction approach using 2% v/v acetic anhydride in toluene. The main reason for the better recovery obtained in this way, in comparison with the classical ASE approach, is to overcome strong matrix-analyte interactions. Analogously, fatty acids were analyzed as methyl esters obtained by in-situ derivatization/extraction using boron trifluoride. Received: 28 December 1998 / Revised: 16 February 1999 / Accepted: 21 February 1999     

Sodium Hydroxide (NaOH)-Mediated Oxidative Hydroxylation of Arylboronic Acids and Its Applications in C-O Bond Formation

We have developed a straightforward methodology for converting arylboronic acids into phenols using NaOH-mediated air oxidation. This reaction offers several advantages, including simple operation, excellent tolerance towards various functional groups, and scalability. The transmetalation of the resulting borate ester with NaOH occurs readily, enabling convenient derivatization of the borate ester into aryl ethers and esters using alkyl and acyl halides.     

薄层色谱-热辅助水解甲基化-气相色谱法测定生物柴油中的甘油酯

建立了薄层色谱-热辅助水解甲基化-气相色谱法测定生物柴油中残余甘油酯含量的方法.样品中的甘油酯经薄层色谱分离,萃取后与三甲基氢氧化硫(0.1 mol/L)各3 μL先后加入到样品杯中,在350℃下,于裂解器中进行衍生化反应,气相色谱测定生成的脂肪酸甲酯,确定甘油酯的含量.生物柴油中常见的甘油一酯、二酯、三酯在60～20...     

Lewis acid-catalyzed ring-opening reactions of methylenecyclopropanes with alcoholic or acidic nucleophiles

[reaction: see text] Methylenecyclopropanes can react with various nucleophiles such as alcohols, phenols, carboxylic acids, and thiols to give the corresponding homoallylic esters or ethers in good yields with good stereoselectivities in the presence of Lewis acids.