Totally found 434 items.

  • [期刊] Determination of gaseous toluene diisocyanate by use of solid-phase microextraction with on-fibre derivatisation
    An SPME method was developed for sampling gaseous 2,4-toluene diisocyanate (2,4- TOI) involving de- rivatisation of the isocyanate by reacting with dibutyl- ilffiine (OBA). The TDI-OBA derivative thus formed was jetermined by LC-MS-MS utilising atmospberic pres- )ure chemical ionisation (APCI). As a first step, OBA was loaded onto a poly(dimethylsiloxane)/divinylbenzene :POMS-OVB) fibre coating by direct vapour-phase ex- :raction of a highly concentrated diethyl ethei solution of DBA. The OBA-Ioaded fibre was then exposed to an arti- lcially generated atmosphere of gaseous 2,4- TDI. The inearity of the method ranged from 52.8 to 3100 I.1g m-3 6.8 to 400 ppbv) with a sampling time of 60 min. The )roposed method has been applied to 2,4- TDI determina- ion in an artificially generated dynamic standard atmo- :phere, yielding an approximate method detection limit MOL) of 21.1g m-3 (0.25 ppbv). This concentration is one wentiet.h of the Occupational Safety and Health Adminis- ration (OSHA) 8-hour time-weighted average (TWA) ex- )osure limit. The sampler with the POMS-OVB-OBA 'oating was found to be stable and retains the required Imount of OBA for at least 10 days, an important feature or sampling systems with potential in-situ applications.
  • [期刊] Determination of trace amounts of lead in mussels by flow-injection flame atomic-absorption spectrometry coupled with on-line minicolumn preconcentration
    A minicolumn packed with poly(aminophos- phonic acid) chelating resin incorporated in an on-line preconcentration system for flame atomic-absorption spectrometry was used to determine ultratrace amounts of lead in mussel samples at Ilg L -I level. The preconcen- trated lead was eluted with hydrochloric acid and injected directly into the nebulizer for atomization in an air-acety- lene flame for measurement. The performance character- istics of the determination of lead were: preconcentration factor 26..8 for 1 min preconcentration time, detection limit (30") in the sample digest was 0.25 Ilg g-1 (dry weight) for a sample volume of 3.5 mL and 0.2 9 sample (preconcentration time 1 min), precision (RSD) 2.3% for 25 Ilg L -I and 2.0% for 50 Ilg L -I. The sampling fre- quency was 45 h-i. The method was highly tolerant of in- terferences, and the results obtained for the determination of lead in a reference material testify to the applicability of the proposed procedure to the determination of lead at ultratrace level in biological materials such as mussel samples.
  • [期刊] Advantages of the iridium permanent modifier in fast programs applied to trace-element analysis of plant samples by eletrothermal atomic absorption spectrometry
    The application of a fast program combined with the advantages of the iridium permanent modifier is proposed for trace element analysis of plant samples by electrothermal atomic absorption spectrometry (ETAAS0. For two volatile elements (Cd, Pb) and two mid-refractory elements (Cr, Ni) it was demonstrated that coating of the platform or of the tube atomization area with Ir is an efficient means of improving the accuracy and precision of results. A detailed study of interference from individual main matrix components and from composite plant martices has confirmed the usefulness of the whole approach. The validity of the method has been confirmed by analysis of eight reference plant materials.
  • [期刊] Separation of vanadium, niobium and tantalum as ternary mixed-ligand complexes by capillary electrophoresis using chelation with 4-(2-pyridylazo)resorcinol and tartaric acid
    Vanadium(V), niobium(V) and tantalum(V) were separated as ternary mixed-ligand complexes by capillary electrophoresis using 4-(2-pyridylazo)resorcinol (PAR) as the color chelating reagent. Four carboxylic acids such as tartaric acid (Tart), oxalic acid, citric acid and acetic acid were investigated as the additional ligand. The first was chosen as the best. Other parameters such as the concentration ratio of Tart to PAR, buffer concentration, injection time and applied voltage were also optimized. Under the optimized conditions, a complete separation of the three metal complexes was accomplished within 10 min. A linear calibration curve in the range of two orders of magnitude was obtained.
  • [期刊] Interpretation of analytical patterns from the output of chaotic dynamic memories
    A fundamental study has been carried out to use a nonlinear dynamic system, Freeman's KIII model, for pattern recognition in analytical chemistry. Filtering of the output of the neuron activity traces in the gamma range has been studied by applying a fast Fourier transform filter. Different possibilities for interpretation of the system output have been investigated. Preliminary reslts are demonstrate for classification of drugs based on their spectra in the mid infrared range.
  • [期刊] Slurry sampling fluorination assisted electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry for the direct determination of metal impurities in aluminium oxide ceramic powders
    A new analytical procedure for the direct determination of metal impurities (Cr, Cu, Fe and V) in aluminium oxide ceramic powders by slurry sampling fluorination assisted electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry (ETV-ICP-AES) is reported. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote the vaporizationof impurity elements inaluminium oxide ceramic powders from the graphite tube. A vaporization stage with a long ramp time and a short hold time provided the possibility of temporal analyte-matrix separation. The experimental results indicated that a 10 #mu#L 1% m/v slurry of aluminium oxide could be destroyed and vaporized completely with 600 #mu#g PTFE under the selected conditions. Two aluminiumoxide ceramic powder samples were used without any additional pretreatment. Anlaytical results obtained by using standard addition method with aqueous standard solution were checked by comparison of the results with pneumatic nebulization (PN)-ICP-AES based on the wet-chemical decomposition and analyte-matrix separation. The limits of detection (LODs) between 0.30 #mu#g g~(-1) (Fe) and 0.08 #mu#g g~(-1) (Cu) were achieved, and, the repeatability of measurements was mainly better than 10%.
  • [期刊] Quantificationof carbohydrate structures in size fractionated aquatic humic substances by two-dimensional nuclear magnetic resonance
    Two-dimensional phase sensitive C,H correlation spectra were successfully applied to the quantification of carbohydrate substructures in aquatic humic substance (HS) fractions obtained by tangential flow multistage ultrafiltration (TFMSTUF) of a selected bog water HS (HO13, German Research Program DFC-ROSIG) as wellas a river HS (Suwannee River Fulvic Aicd Reference of the International Humic Substances Society, IHSS). It turns out that after size fractionation the HS samples give very well resolved C,H-correlation spectra which offer a great potential for substructure quantification. Details of the combined substructure quantification technique, novel in HS characterization, are presented. The results of the combined procedure point out that carbohydrate moieties predominantly occure inhigher molecular mass fractions (> 10 kDa) of isolated HS.
  • [期刊] Example of a technique for evaluation of interferences caused by complicated sample matrix elements in ICP-AES determination
    An example of a useful and rapid procedure for the evaluation of interferences caused by complicated sample matrices in inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. Using simple acid-base standards, all the elements investigated were determined separately i ncomplicated matrices with satisfactory results. Multiple linear regression was used to calculate the linear coorection coefficients for each matrix element analyzed. Good analytical results improved still further when this correction method was used.
  • [期刊] Neurotransmitter sampling and storage for capillary electrophoresis analysis
    Quantitative analysis of signaling molecules from single cells and cellular materials requires careful validation of the analytical methods. Strategies have been investigated that enable single neurons and neuronal tis- sues to be stored before being assayed for many low- weight, biologically active molecules, such as serotonin, dopamine, and citrulline. Both metacerebral cell and pedal ganglia homogenates isolated from Pleurobran- chaea californica have been studied by capillary elec- trophoresis with two complimentary laser-induced fluo- rescence detection methods. For homogenized ganglia samples, several cellular analytes (such as arginine and citrulline) are unaffected by standing at room temperature for days. Many other analytes in the biological matrix, in- cluding the catecholamines and indolamines, degrade by 20% within 10 h at room temperature. Rapidly freezing samples or preserving them with ascorbic !lcid preserves more than 80% of the dopamine and about 70% of the serotonin even after five days. In addition, serotonin and dopamine remain completely stable for at least five days by combining the ascorbic acid preservation and freezing at -20°C. The timing of preservation is critical in main- taining the original composition of the biological samples. Using our optimum storage protocol of freezing the sam- ple within 2 h after isolation, we can store frozen ho- mogenate ganglia samples for more than four weeks be- fore assay while still obtaining losses less than 10% of the original serotonin and dopamine. The nanoliter-volume single cell samples, however, must be analyzed within 4 h to obtain losses of less than 10% for serotonin related metabolites.
  • [期刊] Comparative assessment of two sequential chemical extraction schemes for the fractionation of cadmium, chromium, lead and zinc is surface coastal sediments
    Two existing sequential chemical extraction schemes. involving respectively five and six leaching steps with solutions of increasing dissolving power, were com- pared. The methods have been applied to surface sediment samples collected in a marine estuary zone potentially ex- posed to contamination arising from nearby industrial ac- tivities. A certified reference material (MURST-ISS-Al) .consisting of an Antarctic bottom sediment for which no information regarding phase dep~ndent concentration is available, was also analyzed. In order to evaluate the par- tition of metals among different geochemical forms, the concentrations of cadmium, chromium, lead and zinc were measured in the liquid extracts by Zeeman-corrected flame atomic absorption and by inductively coupled plasma-atomic emission spectrometry. The total metal concentrations were determined after strong acid attack, and the adequacy of this total digestion/dissolution tech- nique was verifi~,d by its application to the reference ma- terial. Comparison of total metal concentrations with the sum of concentrations associated with the individual phases was employed to assess possible analyte losses or contaminations. Precisions for both sequential procedures were comparab.le, but some inconsistencies in mass bal- ances were found in one of the samples for the distribu- tionof Zn in the soluble/exchangeable fractions and for Cd in the bound to carbonates form. In addition, the six steps procedure produced I.ower concentration values in the case of elements associated to the residual fraction.