The efficiency of alkaline extraction for the recovery of hexavalent chromium (CrVI) from paint samples and the effect of sample storage on CrVI recovery

Workplace exposures to CrVI, a human carcinogen, are significant in spraying operations of chromate-containing paints. Accurate determination of CrVI in paint aerosol air samples is important in assessing a worker's exposure to CrVI. National Institute for Occupational Safety and Health method 7604 is widely used for determining CrVI in air samples. It utilizes an alkaline extraction procedure. It was historically validated for paint aerosol samples containing 24.5 to 61.5 microg of CrVI. The literature documented potential airborne CrVI exposures greater than 61.5 microg in recent paint spraying operations. The efficiency of the alkaline method at extracting CrVI from paint samples containing 250 to 3000 microg of CrVI was determined. Paint was prepared, sampled, extracted twice and then digested. Extracts were analyzed for CrVI and digestates of the residual Cr were analyzed for total Cr. Alkaline extraction of paint samples using NIOSH method 7604 resulted in quantitative recoveries for paint samples with CrVI filter loadings from 250 to 3000 microg. A decrease in CrVI extraction efficiency was observed in samples containing > 1000 microg of CrVI. A second extraction improved the recovery of CrVI in these samples. Refrigerating paint aerosol samples for up to 2 weeks did not affect their CrVI content.     

The interaction of dolomite surfaces with metal impurities: a computer simulation study

This study investigates the behaviour of selected, morphologically important surfaces of dolomite (CaMg(CO3)2), using computational modelling techniques. Interatomic potential methods have been used to examine impurity substitution at cationic sites in these surfaces. Environmentally prevalent cations were studied to this end, namely Ni2+, Co2+, Zn2+, Fe2+, Mn2+ and Cd2+, all of which are also found as end-member carbonate minerals. Solid-solution substitution was investigated and showed that Cd and Mn will substitute from their end-member carbonate phase at either dolomite cation site. Mn is found to preferentially substitute at Mg sites, in agreement with experimental findings. For Ni2+, Co2+ and Zn2+, the magnitude of substitution energies is approximately equal for all surfaces, with the exception of the (1014) surface. However, for the larger cations, a far greater disparity in substitution energies is observed. At a stepped surface, analogous substitutions were performed and it was found that substitution energies for all impurity cations were reduced, indicating that uptake is more viable during growth. The predominant surface, the (1014), was solvated with a monolayer of water in order to investigate the influence of hydration on substitution energetics. The addition of water changes the relative preference for substitution of the different cations. Under aqueous conditions, the substitution energy is determined by three competing factors, the relative importance of which cannot be predicted without this type of computational investigation.     

A liquid chromatography/tandem mass spectrometry method for the simultaneous quantification of isoniazid and ethambutol in human plasma

Isoniazid and ethambutol are commonly used in various combination treatments for tuberculosis, and for this reason a rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was developed and validated for simultaneous quantification of these two drugs in human plasma. After a simple protein precipitation using methanol, the analytes and the internal standard metformin were chromatographed on a C18 column and detected by MS/MS. An atmospheric pressure chemical ionization interface was chosen to reduce ion suppression from sample matrix components and provide high sensitivity. The LC retention times for isoniazid and ethambutol were 2.46 and 2.27 min, respectively. The method was linear in the concentration range of 10.0-5000 ng/mL for each analyte using 100 microL plasma. The intra- and inter-day precisions, expressed as the relative standard deviation (RSD), were less than 5.7 and 6.4%, determined from QC samples for isoniazid and ethambutol, and the accuracies were within +/-2.1% and +/-4.5% in terms of relative error, respectively. The method was successfully employed in a pharmacokinetic study after oral administration of a multicomponent formulation containing 150 mg isoniazid, 500 mg ethambutol, 150 mg rifampicin and 250 mg pyrazinamide.     

Characterization of Endogenous Protoporphyrin IX Induced by δ-Aminolevulinic Acid in Resting and Activated Peripheral Blood Lymphocytes by Four-Color Flow Cytometry

Lymphocytes treated with δ-aminolevulinic acid (ALA) can accumulate the photoactive, fluorescent heme precursor, protoporphyrin IX (PpIX). With visible light illumination, PpIX can be used in photodynamic therapy (ALA-PDT) to kill or functionally alter cells. The aim of this study was to characterize the effects of ALA and ALA-PDT on resting and activated human peripheral blood T lymphocytes. Accumulation of PpIX depends inversely on the rate of its iron-dependent conversion into heme. Activated, replicating lymphocytes have low intracellular iron levels, with corresponding increases in the transferrin receptor (CD71). Thus, we expected activated lymphocytes would preferentially accumulate PpIX. Using four-color flow cytometry, we examined ALA-induced PpIX levels in T-cell subsets of resting and activated human peripheral blood mononuclear cells and the relationship between CD71 and PpIX. Peripheral blood mononuclear cells stimulated by phytohemagglutinin (PHA) were simultaneously phenotyped for PpIX, CD71 and the T-cell markers CD3 and CD4 or CDS. In activated cells treated with 0-6mM ALA for 4 h, PpIX fluorescence was maximal at 1 mM ALA. On a single cell basis, there was a strong correlation between PpIX ac-cumulation and CD71 expression. The ALA-treated, PHA-stimulated, CD71⁺ lymphocytes had an eight-fold greater mean PpIX fluorescence than nonactivated, CD71- cells. Approximately 87% of the CD4* and 85% of the CD8⁺ T cells accumulated PpIX. The PpIX levels of CDS⁺ cells were about 5% greater than CD4⁺ cells. In addition, mixed lymphocyte reaction-stimulated cells treated with ALA accumulated more PpIX than controls. Thus, activated cells preferentially accumulate endogenous PpIX when exogenous ALA is administered. Cytotoxicity studies showed that the majority of the activated cells following ALA-PDT were killed but resting cells were spared. Also, in examining activation markers by flow cytometry the number of cells that were positive for activation markers CD38 or CD71 dramatically decreased after ALA and light treatment in activated populations. The data suggest a role for ALA-PDT as an immunomodulator or photocytotoxic agent targeting activated lymphocytes.     

Synthesis,properties and crystal structures of R[MIII(bdt)2] complexes (M = Ni,Co, Cu)

New nickel, cobalt and copper complexes with benzene-1,2-dithiole (bdt), of general formula R[M(bdt)₂]: M = Ni, Co and Cu; R = Me₄N, Et₄N, Pr₄N, Me₃PhN, MePh₃P, Ph₄P have been synthesized and characterized by standard physico-chemical methods (elemental analyses, magnetochemical and conductivity measurements, i.r. and u.v.–;vis. spectroscopy). X-ray structural analysis of (MePh₃P)[M(bdt)₂], M = Ni, Co and Cu, confirms that the MS₄ chromophore lies in a slightly distorted square coordination arrangement around the central atom. The three complexes have also been studied by cyclic voltammetry.     

The Early Picosecond Photophysics of Ru(II) Polypyridyl Complexes: A Tale of Two Timescales

The early picosecond time scale excited-state dynamics of the paradigm tris(2,2'-bipyridyl)Ruthenium(II) ([Ru(bpy)(3)](2+)) and related complexes have been examined by picosecond Kerr-gated time-resolved resonance Raman (ps-TR(3)) spectroscopy. The evolution of the signature Raman bands of the lowest thermally equilibrated excited (THEXI) state under two-color pump/probe conditions show that this state is not fully populated within several hundred femtoseconds as proposed previously but rather only within the first 20 ps following excitation. In addition to an emission observed within the instrument rise time (τ < 3 ps), the early picosecond dynamics are characterized by a rise in the intensity of the Raman marker bands of the THEXI-(3)MLCT state, a rise time which, within experimental uncertainty, is not influenced by either partial or complete ligand deuteriation or the presence of ligands other than bpy, as in the heteroleptic complexes [Ru(bpy)(2)(L1)](+) and [Ru(bpy)(2)(Hdcb)](+) (where H(2)dcb is 4,4'-dicarboxy-2,2'-bipyridine and L1 is 2,-(5'-phenyl-4'-[1,2,4]triazole-3'-yl)pyridine). Overall, although the results obtained in the present study are consistent with those obtained from examination of this paradigm complex on the femtosecond timescale, regarding initial formation of the vibrationally hot (3)MLCT state by ISC from the singlet Franck-Condon state, the observation that the THEXI-(3)MLCT state reaches thermal equilibration over a much longer time period than previously suggested warrants a re-examination of views concerning the rapidity with which thermal equilibration of transition metal complex excited states takes place.     

Role of short-range electrostatics in torsional potentials

A force field needs to decide if it should contain a torsional potential or not. A helpful guide to this decision should come from a quantum mechanical energy partitioning. Here we analyze the energy profiles of eight simple molecules (ethane, hydrogen peroxide, hydrazine, methanol, acetaldehyde, formamide, acetamide and N-methylacetamide) subject to rotation around a torsion angle. Coulomb interaction energies between all atom pairs in a molecule are monitored during the rotation. Atoms are defined as finite electron density fragments by quantum chemical topology, a method that enables well-defined short-range interactions (1-2, 1-3 and 1-4). Energy profiles of Coulomb interaction energies mostly counteract the ab initio energy profiles. This and future work strives to settle ambiguities in current force field design.     

A metallopolymer case-history: polymer, ring or ligand reaction?

Multinuclear cobalt(II) complexes of ditopic ligands with alpha,omega-dioxy spacers linking two tpy metal-binding domains react with alcohols to generate mononuclear 4'-alkoxy-species.     

Successive determination of urinary protein and glucose using spectrophotometric sequential injection method

A new sequential injection (SI) system with spectrophotometric detections has been developed for successive determination of protein and glucose. The protein assay is based on ion-association of protein with tetrabromophenolphthalein ethyl ester (TBPE) in the presence of Triton X-100 at pH 3.2. The blue product is monitored for absorbance at 607 nm. For glucose, hydrogen peroxide, generated by the oxidation of glucose in the presence of glucose oxidase immobilized on glass beads packed in a minicolumn, is monitored using iron-catalyzed oxidation reaction of p-anisidine to form a red colored product (520 nm). The SI procedure takes advantage in performing the protein assay during the incubation period for glucose oxidation. Linear ranges were up to 10 mg dL⁻¹ human serum albumin (HSA) with a limit of detection (LOD) (3σ) of 0.3 mg dL⁻¹, and up to 12.5 mg dL⁻¹ glucose with LOD of 0.08 mg dL⁻¹. R.S.D.s (n = 11) were 2.7% and 2.5% (for 1 mg dL⁻¹ and 5 mg dL⁻¹ HSA) and 1.4% (9 mg dL⁻¹ glucose). Sample throughput for the whole assay of both protein and glucose is 6 h⁻¹. The automated system has been demonstrated for the successive assay of protein and glucose in urine samples taken from diabetic disease patients, with good agreement with the other methods. This developed SI system is an alternative automation for screening for diabetic diagnosis.