Fabrication and Determination of Refractive Index Profile of the Planar Waveguides by Wedge Technique

Several planar waveguides have been fabricated. The waveguides have been polished for determination of their refractiveindex profiles (RIP) by wedge method. The RIP determined by inserting the sample in a Mach-Zehnder interferometer andapplying fringe analysis methods.     

Solid-liquid extraction and preconcentration of trace nickel using 2-nitroso-1-naphthol-4-sulfonic acid (Nitroso-S) and TDBA onto benzophenone and determination by atomic absorption spectrometry.

Nickel was quantitatively retained by 2-nitroso-1-naphthol-4-sulfonic acid (Nitroso-S) and tetradecyldimethylbenzylammonium chloride (TDBA Cl) onto benzophenone in the pH range 5.0-6.0 from large volumes of aqueous solutions of various samples. After filtration, each solid mass consisting of a nickel complex and benzophenone was dissolved with 5 ml of dimethylformamide (DMF) and the metal was determined by atomic absorption spectrometry (AAS). About 0.6 microg of nickel could be concentrated from 200 ml of an aqueous sample, where its concentration was as low as 3.0 ng/ml. Eight replicate determinations of 2.5 microg/ml of nickel in the final DMF solution gave a mean absorbance of 0.112 with a relative standard deviation of 1.9%. The sensitivity for 1% absorption was 98 ng/ml. The interference of a number of anions and cations was studied and the developed optimized conditions were utilized for the trace determination of nickel in various alloys and biological samples.     

Chiral capillary electrophoresis-mass spectrometry: modes and applications

A review is presented to highlight several approaches for coupling capillary electrophoresis (CE) and electrospray ionization-mass spectrometry (ESI-MS) for analysis of chiral compounds. A short discussion of commercially available CE-MS instruments and interface design is followed by a detail review on various modes of chiral CE-MS. In general, for each CE-MS mode, the capabilities, applications and limitations for chiral analysis have been pointed out. The first mode, chiral capillary zone electrophoresis-mass spectrometry (CZE-MS) in which neutral derivatized cyclodextrins (CDs) are used is possible using either column coupling with voltage switching or a partial-filling technique (PFT). However, some applications of direct coupling of CZE-MS mode are also reported. The second mode is a chiral electrokinetic chromatography-mass spectrometry (EKC-MS) in which a charged chiral selector such as a sulfated beta-CD or a vancomycin could be conveniently employed. This is because these chiral selectors have a significantly higher countercurrent electrophoretic mobility which prevents the entrance of these selectors into the mass spectrometer. The combination of counter-migration and PFT demonstrates that this synergism could be successfully applied to chiral analysis of a broader range of compounds. It is well-known that the on-line coupling of micellar electrokinetic chromatography to mass spectrometry (MEKC-MS) is problematic because the high surface activity and nonvolatile nature of conventional surfactant molecules lower the electrospray ionization efficiency. However, a recent report demonstrates that this hyphenation is now possible with the use of molecular micelles. Various MEKC-ESI-MS parameters that can be used to optimize both chiral resolution and ESI response are discussed. Finally, two recent examples that demonstrate the feasibility of using either open-tubular or packed chiral CEC with MS are reviewed. This survey will attempt to cover the state-of-the-art on various modes of CE-MS from 1998 up to 2002.     

New insights into ethene epoxidation on two oxidized Ag[111] surfaces

Reaction mechanisms and activation energies for the complete conversion of ethene to ethene epoxide on two recently characterized oxidized Ag{111} surfaces have been determined from density functional theory. On both surfaces, epoxidation proceeds through a two-step nonconcerted mechanism via an oxametallacycle intermediate. The key implications are that both surfaces are active and that epoxidation can take place over a wide O coverage regime.     

Capillary electrochromatography of Triton X-100

Nonionic surfactants such as Triton X-100 (TX-100) are comprised of a mixture of oligomers with a varying degree of length in the ethoxylate chain. The development of chromatographic methods for resolution of the various oligomers of TX-100 is of environmental importance, and can be useful for quality control and characterization in industrial manufacture. Capillary electrochromatography (CEC) is fast becoming a capable separation technique that combines the benefits of both high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). This report presents a novel CEC method for separation of the various TX-100 oligomers. A comparison of monomeric vs. polymeric stationary phases for separation of TX-100 was conducted. Since the oligomers of TX-100 were better resolved on a monomeric phase as compared to polymeric phase, a systematic mobile phase tuning was performed utilizing a monomeric CEC-C18-3 microm-100 A stationary phase. Various mobile phase parameters such as acetonitrile (ACN) content, Tris concentration, pH, voltage, and temperature were manipulated in order to achieve the optimum separation of oligomers in less than 30 min.     

Micellar electrokinetic chromatography of polychlorinated biphenyl congeners using a polymeric surfactant as the pseudostationary phase

Micellar electrokinetic chromatography (MEKC) of highly hydrophobic compounds is generally difficult using sodium dodecyl sulfate micellar solutions. The polymeric surfactant, polysodium undecyl sulfate (poly-SUS) has been used to separate moderately to highly hydrophobic polychlorinated biphenyl (PCB) congeners by MEKC in the absence of cyclodextrins. Parameters such as concentration of acetonitrile (ACN), polymeric surfactant concentration, and the effect of pH were examined. Optimum MEKC conditions to get baseline resolution of nine PCBs was 7.5 mM borate in 40% (v/v) ACN fraction buffered at pH 9.2 using 0.5% (w/v) poly-SUS. The applied voltage was 30 kV and the temperature was maintained at 25 degrees C. Elution order for each PCB congener was found to be dependent on the degree of chlorination and hydrophobic character.     

Polymeric sulfated surfactants with varied hydrocarbon tail: I. Synthesis, characterization, and application in micellar electrokinetic chromatography

The influence of surfactant hydrocarbon tail on the solute/pseudostationary phase interactions was examined. Four anionic sulfated surfactants with 8-, 9-, 10-, and 11-carbon chains having a polymerizable double bond at the end of the hydrocarbon chain were synthesized and characterized before and after polymerization. The critical micelle concentration (CMC), polarity, and aggregation number of the four sodium alkenyl sulfate (SAIS) surfactants were determined using fluorescence spectroscopy. The partial specific volume of the polymeric SAIS (poly-SAIS) surfactants was estimated by density measurements and capillary electrophoresis (CE) was employed for determination of methylene selectivity as well as for elution window. The CMC of the monomers of SAIS surfactants decrease with increase in chain length and correlated well when fluorescence method was compared to CE. The physicochemical properties (partial specific volume, methylene selectivity, electrophoretic mobility, and elution window) increased with an increase in chain length. However, no direct relationship was found between the aggregation number and the length of hydrophobic tail of poly-SAIS surfactants. These polymeric surfactants were then used as pseudostationary phases in micellar electrokinetic chromatography (MEKC) to study the retention behavior and selectivity factor of 36 benzene derivatives with different chemical characteristics. Although variation in chain length of the polymeric surfactants significantly affects the retention of nonhydrogen bonding (NHB) benzene derivatives, these effects were less pronounced for hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) benzene derivatives. Therefore, hydrophobicity of poly-SAIS surfactants was found to be a major driving force for retention of NHB derivatives. However, for several benzene derivatives (NHB, HBA, and HBD) significantly higher selectivity factor was observed with longest chain polymeric surfactant (e.g., poly(sodium 10-undecenyl sulfate), poly-SUS) compared to shorter chain polymeric surfactant (e.g., poly(sodium 7-octenyl sulfate), poly-SOcS). In addition, the effect of the surfactant hydrophobic chain was also found to have some impact on migration order of NHB, HBA, and HBD benzene derivatives.     

Capillary electrochromatography of methylated benzo[a]pyrene isomers. II. Effect of stationary phase tuning

For Part II of our ongoing study, we present a strategy for stationary phase optimization for the capillary electrochromatographic (CEC) separation of the 12 methylated benzo[a]pyrene (MBAP) isomers. Utilizing the optimum mobile phase conditions from Part I of our study as a guide, seven commercially available stationary phases have been evaluated for their ability to separate highly hydrophobic MBAP isomers. Ranging in design from high-performance liquid chromatography (HPLC) to CEC application, each phase was slurry packed in house and tested for CEC suitability and performance. Several stationary phase parameters were investigated for their effects on MBAP separation including bonding type (monomeric or polymeric, % carbon loading, surface coverage), pore size, particle size, and type of alkyl substituent. In this manner, the present state of commercially available packings has been assessed in our laboratory. Utilizing the optimum polymeric C18-5 microm-100 A-PAH stationary phase, the effects of CEC packed bed length and capillary inside diameter (I.D.) were also evaluated. A 50 microm I.D. capillary, 25 cm packed bed length and 75% (v/v) acetonitrile, 12.5 mM Tris, pH 8.0, 20 degrees C at 30 kV, provided resolution of 11 out of 12 MBAP isomers thus showing the effectiveness of CEC for analysis of structurally similar methylated polyaromatic hydrocarbons.