Drying agents for water-free introduction of desorption solvent into a GC after on-line SPE of aqueous samples

Summary A small cartridge containing a drying agent is inserted between a solid phase extraction (SPE) column and a gas chromatograph (GC) to enable the introduction of water-free desorption solvent into the GC in on-line liquid chromatography (LC)-type enrichment of trace-level analytes from water samples. Some characteristics of the drying agents, such as their capacity to retain water and their re-usability after heating, have been tested. Possible interactions of the drying agent with the analytes, e.g., irreversible adsorption or catalyzed degradation, have been checked for a wide range of alkanes, alkylbenzenes chlorobenzenes, chlorophenols and phthalate esters. Using the on-line SPE-GC system with flame ionization detection (FID) and spiked samples containing different levels of the test compounds, the repeatability was shown to be satisfactory (6–17%). For 10 mL samples, the detection limits were lower than 0.1 g/L. The on-line SPE-GC-FID system here presented can be used for the repeated analysis of water samples without exchange of the dyring cartridge. The technique is applied to the analysis of tap water.     

The preparation of immobilized polysiloxane coated on packings materials for high-pressure gas chromatography

Summary In high pressure gas chromatography efficient columns can be packed by the slurry packing technique. However, polysiloxane stationary phases like OV 101 and OV 3 dissolve in the packing liquids. In order to make them suitable for slurry packing these stationary phases have to be made insoluble. This immobilization is achieved by bonding the stationary phases to the surface by means of a high temperature treatment. Successive layers are applied by recoating and are immobilized by a cross-link reaction. A range of loading percentages from 4 upto 20 by weight could be prepared in this way. On the evaluated columns compounds like butanol and dioxane elute as rather symmetrical peaks with the correct values for the retention index, indicating the absence of adsorption effects. Efficiency is good and bleeding rate is low. The columns could be successfully used in the analysis of turpentines.     

Selective and sensitive detection of organic contaminants in water samples by on-line trace enrichment–gas chromatography–mass spectrometry

Liquid chromatographic (LC) type trace enrichment is coupled online with capillary gas chromatography (GC) with mass spectrometric (MS) detection for the analysis of aqueous samples. A volume of 1–10 ml of an aqueous sample is preconcentrated on a trace-enrichment column packed with a polymeric stationary phase. After cleanup with HPLC-grade water the precolumn is dried with nitrogen and subsequently desorbed with ethyl acetate. A fraction of 60 μl is introduced on-line into a diphenyltetramethyldisilazane-deactivated retention gap under partially concurrent solvent evaporation conditions and using an early solvent vapor exit. The analytes are separated and detected by means of GC–MS. The potential of the LC–GC–MS system for monitoring organic pollutants in river and drinking water is studied. Target analysis is carried out with atrazine and simazine as model compounds; the detection limits achieved under full-scan and multiple ion detection conditions are 30 pg and 5 pg, respectively. Identification of unknown compounds (non-target analysis), is demonstrated using a river water sample spiked with 168 pollutants varying in polarity and volatility.     

The derivatization of fatty acids by (chloro)alkyl chloroformates in non-aqueous and aqueous media for GC analysis

Fatty acids can be conveniently derivatized in less than one minute with (chloro)alkyl chloroformates such as methyl chloroformate, 2-chloroethyl chloroformate and 2,2,2-trichloroethyl chloroformate. 2,2,2-Trichloroethyl chloroformate is the most reactive reagent, and yields a reaction product which can be sensitively detected by GC ECD (detection limit 50 ng/ml, i.e. 25 pg/injection, for C⁸, C¹⁰, and C¹² acids). In non-aqueous media 3-picoline, N-methylpiperidine, and dimethylaminopyridine show catalytic activity comparable with that of pyridine and can, therefore, replace it. N-methylpiperidine is the best basic catalyst in aqueous media (i.e. media containing up to 40 % water).     

Comparative study of the electronic structure of the ordered and disordered Cu3Au (100) and Cu3Au (110) surfaces

The influence of structural changes on the electronic structure has been investigated by a comparison of the angle-integrated valence and core level photoelectron spectra of ordered and disordered Cu₃Au(100) and (110) surfaces. The total width of the Au 5d and Cu 3d bands does not change with the ordering state or surface orientation. The spectra for the (100) surface are compared with selfconsistent calculations and good agreement is found, for the ordered state, however with a 0.6 eV correction of the calculated Fermi level position. We observe three Au 5d derived bands at 5.1, 6.0 and 6.9 eV, in contrast to previous experimental findings. Our results indicate the existence of shortrange order above the critical temperature.     

Photoemission study (XPS,UPS) of PuFe2

XPS and UPS investigations of PuFe₂ add support to the claim that Pu 5f electrons are localized in this compound. The surface composition is similar to that of lanthanide—transition metal compounds. Some capacity for surface healing has been observed after exposure to the atmosphere.     

Spectroscopy and Defect Identification for Fluorinated Carbon Nanotubes

Finely tuned: Carbon nanotubes are exposed to a CF₄ radio‐frequency plasma (see picture). High‐resolution photoelectron spectroscopy shows that the treatment effectively grafts fluorine atoms onto the MWCNTs, altering the valence electronic states. Fluorine surface concentration can be tuned by varying the exposure time.

     

Preparation of organic nanoparticles using microemulsions: their potential use in transdermal delivery

Organic nanoparticles of cholesterol and retinol have been synthesized in various AOT (Aerosol OT; sodium bis(2-ethylhexyl) sulfosuccinate)/heptane/water microemulsions by direct precipitation of the active principle in the aqueous cores. The nanoparticles are observed by transmission electron microscopy (TEM) using the adsorption of a contrasting agent, such as iodine vapor. The size of the nanoparticles can be influenced, in principle, by the concentration of the organic molecules and the diameter of the water cores, which is related to the ratio R=[H2O]/[surfactant]. The particles remain stable for several months. The average diameter of the cholesterol nanoparticles varies between 3.0 and 7.0 nm, while that of retinol varies between 4.0 and 10 nm. The average size of the cholesterol nanoparticles does not change much either as a function of the ratio R or as a function of the concentration of cholesterol. The constant size of the nanoparticles can be explained by the thermodynamic stabilization of a preferential size of the particles. Chloroform is used to carry the active principle into the aqueous cores. Retinol molecules form J-complexes composed of two or three molecules, as detected by UV-visible spectroscopy.     

Liquid chromatography — Particle beam mass spectrometry for identification of unknown pollutants in water

Summary Trace enrichment on a precolumn packed with copolymer material, coupled on-line with reversed-phase, column liquid chromatography-particle beammass spectrometry (RPLC-PB-MS) has been used for both target and non-target analysis of water samples. RPLC is carried out on a C-18-bonded silica column using a linear acetonitrile-0.1 M ammonium acetate gradient. Using optimised PB-MS conditions and 100–250 ml water samples, the detection limits for several phenylureas are in the 0.03–0.05 g l^–1 range using the full-scan mode; repeatability is good and the LC-PB-MS system is robust. Several surface and drinking water samples have been analysed and low levels of various environmental contaminants have been identified using electron impact mass spectra. Applying chemical ionisation with methane as reagent gas in both the positive and negative mode in conjunction with PB-MS provides relevant confirmatory information.