Ionel Ciucanu

A simple and rapid method for the permethylation of carbohydrates

Abstract As a result of a study of the permethylation of sugars in such dipolar aprotic solvents as methyl sulphoxide, the hitherto accepted role of the CH3SOCH−2 anion is questioned. The HO− and H− ions appear to be the effective basic agents in these methylation reactions. This conclusion suggested a new method for the permethylation of sugars involving methyl iodide, a solid base (NaOH, KOH, or tert-BuOH/NaOH), and methyl sulphoxide. Excellent yields (98 ±2%) of permethylation products were obtained in a remarkably short (6–7 min) reaction time. The non-sugar peaks that appear in gas chromatograms of the products of Hakomori methylation were absent when the new reagent was used.

Rapid and simultaneous methylation of fatty and hydroxy fatty acids for gas—liquid chromatographic analysis

Abstract Rapid and exhaustive methylation of fatty acids and hydroxy fatty acids may be achieved using methyl in polar aprotic organic solvents such as dimethylacetamide and in the presence of sodium hydroxide or potassium hydroxide. The optimal proportion between the lipid sample, methyl iodide, alkali metal hydroxide and solvent were established empirically. The method is suitable for the gas—liquid chromatographic determination of the total fatty acid composition of lipid mixtures.

Avoidance of degradation during the methylation of uronic acids

Abstract The action of various strong bases during the methylation of uronic acids has been studied in order to establish conditions that cause a minimum of degradation. The system methyl iodode-sodium hydroxidemethyl sulphoxide gave good yields of methylated uronic acids if the methyl iodide was added before the base. The methylation products were analysed by g.l.c.-m.s.

Solid phase microextraction assisted by droplets-based liquid–liquid microextraction for analysis of volatile aromatic hydrocarbons in water by gas chromatography

A new technique for the analysis of volatile aromatic hydrocarbons by combining liquid-liquid microextraction with solid phase microextraction has been developed. The analytes were extracted from aqueous samples by an immobilized polydimethylsiloxane fiber assisted by the droplets of an appropriate organic solvent. Benzene, toluene, ethylbenzene, and o-xylene were used as target analytes. The main factors potentially affecting the microextraction such as the nature and the volume of organic solvent, polydimethylsiloxane (PDMS) swelling, extraction time, agitation, temperature, and salts were optimized. The method requires a very low consumption of organic solvent. The relative enrichment factor is in the range of 7.1-32.4 for extraction in the presence of dichloromethane at an optimum volume of 18 μL mL(-1) of aqueous sample. This enhancement over regular polydimethylsiloxane fiber is primarily the result of the fiber swelling and of a stable thin layer of organic solvent attached to the surface of the PDMS fiber. The limit of detection ranges from 0.02 to 0.65 ng mL(-1) for the target compounds using a 7-μm bonded polydimethylsiloxane coating and a flame ionization detector. The validity of this method is demonstrated by the analysis of a real waste water sample.

Membrane and trap system for continuous monitoring of volatile organic compounds using a portable gas chromatograph with thermal conductivity detector

A device for continuous monitoring of volatile organic compounds by collection of analytes by membrane permeation followed by their concentration on a solid sorbent and injection into a gas chromatograph on thermal desorption is presented. The transfer line between the small trap and the gas chromatograph is a resistance-heated silicosteel capillary column which effects pre-separation or separation of analytes. The device performs automatic injections, is portable because it is powered by a 12-V DC battery, and is light since it incorporates a small carrier gas cylinder and a micro thermal conductivity detector (TCD). Factors affecting the sensitivity of the TCD in the membrane and trap system were evaluated. Separation is performed in less than 30 s for benzene, toluene, trichloroethylene, and tetrachloroethylene, the resolution and peak shapes are very good, and the limits of detection under these experimental conditions were 25 ppt, 30 ppt, 85 ppt, and 90 ppt, respectively. The device was tested for continuous monitoring of thermo-oxidative degradation products of polystyrene.

Continuous permeation of analytes through a thin poly(dimethylsiloxane) membrane followed by sorbent trapping for their gas chromatographic monitoring

Parameters that affect the permeation of analytes across a thin (0.025 mm) flat membrane of polysiloxane in a membrane and trap interface coupled to a gas chromatograph are examined taking into account a mechanism of mass transport for porous and nonporous materials and the permeation of carrier gas in the direction opposite to that of the analytes. The best permeation rate was reached with hydrogen as carrier gas at a flow-rate between 3 and 5 ml/min, an agitation of analytes outside the membrane above 0.4 m/s and thin membrane. The parameters that affect the residual diffusion time of analytes in membrane were also examined. A practical application of the thin membrane in membrane and trap interface was demonstrated by gas chromatographic monitoring of six volatile organic compounds in air. The limit of detection is at the nmol/ml level depending on the time of trapping and the parameters that affect the permeation through the membrane.

Derivatization of prostaglandis and related compounds to (methoxime) alkyl ester alkyl ether derivatives for gas chromatographic analysis

Rapid and convenient methods are described for the exhaustive derivatization of carbonyl, carboxyl and hydroxyl groups of prostaglandins and related compounds to methoxime, alkyl ester and alkyl ether compounds respectively. Optimal reaction conditions were established for each group. The reactions were carried out in polar aprotic solvents. Alkyl ester alkyl ether derivatives were obtained quantitatively and rapidly in one step with n-alkyl (C1C4) halides in the presence of sodium hydroxide. Methyl ester methyl ether derivatives have the highest volatility, but propyl ester propyl ether derivatives improved the separation of complex mixtures. The cabonyl group sometimes induced side-products, so the carbonyl group was converted into methoxime. Methoximation was achieved quantitatively by using methoxylamine in the presence of hydrochloric acid or sodium hydroxide, followed by alkylation in same reaction medium. Methoximation gave syn- and anti-isomers, which were separated chromatographically, decreasing the resolution for complex samples.

Quantitative evaluation of perchlorethylene in groundwater before and after its oxidation by helical solid sorbent extraction and gas chromatography

An integrated method of dynamic extraction of perchloroethylene (PCE) with polydimethylsiloxane (PDMS) helical solid sorbent followed by injection into a gas chromatograph was developed for the determination of the real concentration of PCE in groundwater before and after its degradation by oxidation with KMnO(4). The main parameters (agitation, temperature, salts, pH) that affect the extraction efficiency have been evaluated and optimized. The increase of the extracted amount of PCE due to the presence of the salts could be partially compensated by the opposite effect of the insoluble MnO(2), and of the presence of HCl and the global effect of the matrix would be less important for the reproducibility of the PCE extraction. The quantitative analysis of PCE was carried out with the external standard method using the calibration-curve technique. The limit of detection for PCE was found of 0.05 mg L(-1) using flame ionization detector. The solubility of PCE in water was studied by extraction of PCE with PDMS helical solid sorbent from standard solution with different amounts of PCE added into the same volume of water and was found to decrease with settling time, because the fine droplets created during the agitation of the mixture were slowly merged in drops on the bottle walls and were not transferred into the extraction vial for GC analysis. The limit of solubility was evaluated using a graphical method and was estimated at 224.2+/-15.7 mg L(-1) of PCE in water at 25 degrees C.

Determination of Neutral Monosaccharides as Per-O-methylated Derivatives Directly from a Drop of Whole Blood by Gas Chromatography-Mass Spectrometry.

A new analytical procedure was developed for the simultaneous quantification of neutral monosaccharides from a drop of whole blood using gas chromatography-mass spectrometry analysis (GC-MS) of their per-O-methylated derivatives. The per-O-methylation reaction with methyl iodide and solid sodium hydroxide in methyl sulfoxide was used for the first time for analysis of blood monosaccharides. A blood drop volume of 0.6 μL was used without special purification. The elimination of the undesirable components was carried out during methylation in the presence of a strong base and by liquid extraction of the per-O-methylated monosaccharides. The neutral monosaccharides with an anomeric center gave four per-O-methylated isomers, which were well-separated using a capillary column. Identification was done by electron impact mass spectrometry fragmentation, retention times, and library searching. The limits of detection were determined for standards and varied from 2.0 to 2.3 ng mL(-1). Recoveries for human blood samples varied from 99.22% to 99.65%. The RSD values ranged from 1.92 to 2.37. The method is fast, sensitive, reproducible, and an alternative to current methods for quantitative analysis of blood monosaccharides.

Droplets-based microextraction assisted SPME for GC-MS analysis of polar compounds such as clopyralid in water

For the first time, we assessed the performance of liquid phase microextraction (LPME) with droplets of organic solvent that assists solid phase microextraction (SPME) with chemically bonded polydimethylsiloxane (PDMS) fiber for analysis by gas chromatography-mass spectrometry of trace amounts of polar compounds in water. Clopyralid was used as a target analyte. LPME with droplets was performed with dichloromethane and was compared with dispersive liquid–liquid microextraction (DLLME) by addition of acetone or methanol as disperser solvent to dichloromethane. The main factors potentially affecting the microextraction were optimized. The optimal volume of dichloromethane was 17 μL per mL of aqueous samples. The relative enrichment factor for LPME in the presence of dichloromethane droplets was 200 and decreased by addition of disperser solvent. Consequently, DLLME cannot be applied with this SPME fiber. A characteristic of the method is that LPME and SPME can be conducted simultaneously or in two steps in the same vial. The limit of detection and the limit of quantification were 0.02 μg L−1 and 0.07 μg L−1, respectively for 7 μm chemically bonded PDMS fiber and mass spectrometric detection was also carried out.