Capillary electrophoresis for the direct determination of cephalosporins in clinical samples

Summary The possibility of determination of four cephalosporin antibiotics in clinical samples by capillary electrophoresis has been investigated. The separation conditions for capillary zone electrophoresis (CZE) were studied in detail. The precision of migration times measured by use of the optimized method was satisfactory (RSD<1%) and response was linearly dependent on concentration over the approximate range 2–150 mg L⁻¹ for all the compounds studied (cefuroxime, cefotaxime, ceftriaxone, and ceftazidime). Complete separation could be achieved within 5 min. The CZE method was found to be highly suitable for direct determination of the antibiotics in clinical samples such as wound drainage, cerebrospinal fluid, and urine; for serum, however, the use of micellar electrokinetic capillary chromatography (MECC) was more advantageous. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

Plasma Sterilization: A Review of Parameters,Mechanisms, and Limitations

Low-temperature plasma is a promising method for destroying microorganisms, an alternative to conventional methods which have numerous drawbacks. Several plasma-based sterilization technologies are presently under development, but their mechanisms of action are still incompletely understood. Since more than five years, we have investigated the effects of plasma on microorganisms (killing efficacy, and related mechanisms), as well as on the materials being sterilized. This article reports some important observations made during this work, using the commercialized so-called plasma sterilizers and real low-pressure plasma systems. The mechanism of etching (volatilization) of microorganisms by plasma that we have observed, leads us to believe that plasma may constitute a powerful solution to the clinical problems of deactivating also prions and endotoxins. However, plasma effectiveness is influenced by numerous experimental parameters, which we review here. This inherent complexity, and the weak penetrating power of plasma species, that severely limits plasma effectiveness in the presence of organic residues, packaging material, or complex geometries, are the main limitations of plasma sterilization.     

High-speed narrow-bore capillary gas chromatography in combination with a fast double-focusing mass spectrometer

In this work the application of high-speed narrow-bore capillary GC in combination with a fast scanning double focusing magnetic sector mass spectrometer is evaluated. Special emphasis is placed upon detection limits and scan speed in the full scan mode and in the selected ion monitoring mode (SIM). In the full scan mode, up to 20 scans per second could be obtained. The detection limits are in the low picogram range in the full scan mode and improve even to 5 to 50 fg in the SIM mode, depending on the sample complexity and mass resolving power. It will be illustrated that by increasing the resolution in the SIM mode, interferences from ions of the same nominal mass-to-charge ratio as the ions of interest are significantly reduced. Chemical background noise can therefore be largely eliminated, thus enhancing the signal-to-noise ratio.     

Stereoselective synthesis of β-amino ketones via direct Mannich-type reaction catalyzed with silica sulfuric acid

At room temperature, the direct Mannich-type reaction of a variety of in situ generated aldimines using aldehydes and anilines with ketones in a three-component reaction was efficiently catalyzed by silica sulfuric acid (SSA) in EtOH. This rapid reaction afforded the corresponding β-amino ketones in good yields with excellent stereoselectivities and catalyst was recyclable.     

Determination of volatile halogenated hydrocarbons in tap water,seawater and industrial effluents by glass capillary gas chromatography and electron capture detection

A rapid and sensitive method to determine volatile organohalides in different types of waters has been developed. The chromatographic system is based on the resolving power of the glass capillary column and the high sensitivity of the electron capture detector. The capillary columns were connected to the detector so that the eluate from the column is mixed with thermostatted purge gas to minimize band broadening due to dead volumes. The low column bleeding and decreased band spreading from capillary columns enhance the sensitivity to very low levels: 1 fg (10^?15g) for carbon tetrachloride, despite dilution of the column eluate by the purge gas. The water samples of 100 ml were extracted with 1 to 10 ml n-pentane which is the most practical alkane with respect to purity. When using high water to pentane ratios corrections had to be made, due to low extraction yield, to get accurate quantifications. A column with Carbowax 400 stationary phase permits direct tap water injection. The water peak concealed the substances eluated after CHCl₃ and CHBrCl₂. The gas chromatographic separation of haloforms in tap water could be shortened to 30 seconds using a 10 m SE–52 column with an increased film thickness. Besides tap water and seawater, industrial waste water from a pulp mill was analyzed. Ten different halogenated organic compounds, ranging from 1 ng/I to 760 μg/I, were quantified in the different waters. Bromoform, which had not previously been found in seawater, was detected. Chromatogram of a standard mixture containing 11 organohalides. Stationary phase, SE-52; 33 m × 0.3 mm i.d. inj. temp. 200°, column temp. 50°, interface 250°, detector temp. 250°. Helium carrier gas flow rate, 36 cm/s, scavenger'gas flow 30 ml/min. Split ratio 1:20, 1 = CH₂CI₂, 2 = CHC1₃, 3 = CH₃CC1₃, 4 = CC1₄, 5 = CHCICCI₂, 6 = CHBrCI₂, 7 = CBrC1₃, 8 = CHBr₂Cl, 9 = CCl₂CC1₂, 10 = CHCl₂l, 11 = CHBr₃.     

Metal content determination in polymerization catalysts by direct methods

Metal contents in polymerization catalysts were comparatively determined by Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS) and X-ray fluorescence (XRF) spectroscopy. Catalysts were prepared by grafting metallocene onto bare silica or onto silica chemically modified with methylaluminoxane (MAO). Catalysts were compressed as self-supporting pellets (RBS and XRF), or mounted on adhesive copper tape (XPS). The proximity of the mass of the atomic nuclei did not allow resolution by RBS of the signals corresponding to Zr and Nb, nor Si and Al in catalyst systems such as (nBuCp)₂ZrCl₂/Cp₂NbCl₂/MAO/SiO₂. On the other hand, Zr, Nb, Si and Al lines were completely resolved in an XRF spectrum. For supported metallocenes on bare silica, XPS measurement was ca. 40% higher than that obtained by RBS. Silica-supported zirconocene showed good agreement in Zr content determination by XRF and RBS.     

Selective fluorination of an aryl triazolinone herbicide intermediate

Fluoroaryl 1,2,4-triazolin-5-ones are an important class of herbicidal compounds useful in a variety of crop protection applications, primarily for the control of grassy and broad-leaf plant species. While a number of different synthetic strategies can be used for the step-wise preparation of these complex molecules, it is generally preferred to introduce fluorine later in the synthetic pathway, since the presence of fluorine and other halogens has a dominant effect on all subsequent synthetic steps. We have investigated the reactions that occur between aryl triazolinones and a variety of fluorination agents, including F₂/N₂, XeF₂, (CF₃SO₂)₂NF, Selectfluor^®, CF₂(OF)₂, CF₃OF, CH₃COOF, and CF₃COOF, and have used this knowledge to develop several alternative high-yielding routes to fluoroaryl 1,2,4-triazolin-5-ones. The fluorine introduction strategy and experimental results for a representative example of this important class of compounds are discussed herein.     

Multielement trace determination in SiC powders: assessment of interlaboratory comparisons aimed at the validation and standardization of analytical procedures with direct solid sampling based on ETV ICP OES and DC arc OES

The members of the committee NMP 264 “Chemical analysis of non-oxidic raw and basic materials” of the German Standards Institute (DIN) have organized two interlaboratory comparisons for multielement determination of trace elements in silicon carbide (SiC) powders via direct solid sampling methods. One of the interlaboratory comparisons was based on the application of inductively coupled plasma optical emission spectrometry with electrothermal vaporization (ETV ICP OES), and the other on the application of optical emission spectrometry with direct current arc (DC arc OES). The interlaboratory comparisons were organized and performed in the framework of the development of two standards related to “the determination of mass fractions of metallic impurities in powders and grain sizes of ceramic raw and basic materials” by both methods. SiC powders were used as typical examples of this category of material. The aim of the interlaboratory comparisons was to determine the repeatability and reproducibility of both analytical methods to be standardized. This was an important contribution to the practical applicability of both draft standards. Eight laboratories participated in the interlaboratory comparison with ETV ICP OES and nine in the interlaboratory comparison with DC arc OES. Ten analytes were investigated by ETV ICP OES and eleven by DC arc OES. Six different SiC powders were used for the calibration. The mass fractions of their relevant trace elements were determined after wet chemical digestion. All participants followed the analytical requirements described in the draft standards. In the calculation process, three of the calibration materials were used successively as analytical samples. This was managed in the following manner: the material that had just been used as the analytical sample was excluded from the calibration, so the five other materials were used to establish the calibration plot. The results from the interlaboratory comparisons were summarized and used to determine the repeatability and the reproducibility (expressed as standard deviations) of both methods. The calculation was carried out according to the related standard. The results are specified and discussed in this paper, as are the optimized analytical conditions determined and used by the authors of this paper. For both methods, the repeatability relative standard deviations were <25%, usually ~10%, and the reproducibility relative standard deviations were <35%, usually ~15%. These results were regarded as satifactory for both methods intended for rapid analysis of materials for which decomposition is difficult and time-consuming. Also described are some results from an interlaboratory comparison used to certify one of the materials that had been previously used for validation in both interlaboratory comparisons. Thirty laboratories (from eight countries) participated in this interlaboratory comparison for certification. As examples, accepted results are shown from laboratories that used ETV ICP OES or DC arc OES and had performed calibrations by using solutions or oxides, respectively. The certified mass fractions of the certified reference materials were also compared with the mass fractions determined in the interlaboratory comparisons performed within the framework of method standardization. Good agreement was found for most of the analytes.     

Direct Electrochemical Reaction of Horseradish Peroxidase Immobilized on the Surface of Active Carbon Powders

It is reported for the first time that horseradish peroxidase (HRP) immobilized on the active carbon can undergo a direct quasi-reversible electrochemical reaction.In addition,the immobilized HRP showed the stable bioelectrocatalytic activity for the reduction of H2O2.     

Treating large intermediate spaces in the CIPSI method through a direct selected CI algorithm

Summary A general direct selected configuration interaction algorithm has been implemented and coupled to the second-order multireference many-body perturbation theory CIPSI algorithm. The new direct selected CI code is highly vectorizable and able to handle any list of determinants selected to describe a given electronic state of any spin multiplicity. In the present work selection of determinants has been carried out through the CIPSI algorithm but this is not a constraint of the direct selected CI code. The largest case treated so far involves a CI expansion containing 215 260 determinants selected from single and double excitations from 371 references. In this case there were 8 active electrons in 28 molecular orbitals for NH₃ in a DZP basis set. The direct selected CI calculation needs only 14 Mb of central storage (for the 215 260 determinants case) and takes 406 seconds per iteration on an IBM 3090/600J with vector facility.