Comparative study on the use of Ir, W and Zr-coated graphite tubes for the determination of chromium in slurries of human scalp hair by electrothermal atomic absorption spectrometry

The use of Ir, W and Zr-coated graphite tubes, as permanent chemical modifiers, was studied for the determination of chromium in human scalp hair by ETAAS using the slurry sampling technique. The use of Mg(NO₃)₂ and Pd, as aqueous chemical modifiers, was also investigated and compared to the use of the permanent chemical modifiers. Scalp hair samples were pulverized using a Zr vibrational ball mill, (mean particle diameter of 0.8 μm) and suspended in ultrapure water. The lowest limit of detection, 44.5 μg kg^–1,was achieved for the use of W-coated graphite tubes. The repeatability of the overall procedures (slurry preparation and ETAAS determination) were 15.7, 14.5 and 16.7% for W- and Zr-coated graphite tubes and Mg(NO₃)₂, respectively. The methods were applied to several reference materials, CRM 397 (human hair), DOLT-1 (dogfish liver) and DORM-1 (dogfish muscle), and the results obtained were in agreement to the certified values. Finally, the methods were applied to several human scalp hair samples from healthy adults.     

Contribution to the Development of Indirect Atomic Absorption Methods: Application of the Ion Pair 1,10-phenanthroline-mercury(II)-iodide to Iodide Determination in Water and Infant Formulae Samples

A method to determine iodide is developed, based on the formation of an ion pair between 1, 10-phenanthroline, mercury(II) and iodide that can be selectively extracted into IBMK. When the IBMK layer is analyzed by electrothermal atomic absorption spectrometry (ETAAS) for mercury, iodide can be quantified too. Parameters related to the preparation of the ion pair and to the measuring process are studied. Thus, 7.2–7.4 reveals to be the best pH interval to carry out the extraction, and 250 and 1000?°C, respectively, the mineralization and atomization temperatures for mercury determination by ETAAS. The procedure is applied to drinking tap water and commercial infant formulae milk samples. The accuracy of the method has been investigated by means of the analytical recovery for water samples (mean analytical recovery obtained at different concentration levels 98.1%) and by using the certified reference material BCR CRM No 151 Skim Milk Powder (Spiked) for the infant formulae (results within certification interval). The repeatability of the measurements at different concentration levels gave a RSD lower than 10% for both types of samples and the repeatability of the whole procedure for infant formulae shows a RSD of 1.33%. In addition, the limits of detection and quantification were 2.5?μg/L and 8.5?μg/L, respectively, for drinking water and 1.1?μg/g and 3.8?μg/g, respectively, for infant formulae.     

Organo-silica hybrid capillary monolithic column with mesoporous silica particles for separation of small aromatic molecules

Monolithic stationary phases for use in capillary electrochromatography were prepared by incorporation of mesoporous silica particles (of type MCM-41 or UVM-7) in a polymer obtained from butyl methacrylate and ethylene glycol dimethacrylate as monomers, 1,4-butanediol and 1-propanol as porogen, and azobisisobutyronitrile as initiator. The stability of the dispersions with varying fractions of silica particles was investigated by UV-vis spectrometry. Using continuous stirring during the capillary filling and short UV-polymerization times, polymeric beds with homogenously dispersed mesoporous particles (with contents up to 35 wt% of silica) are obtained. The resulting hybrid monolithic columns were characterized using scanning electron microscopy. The chromatographic performance of these novel stationary phases was evaluated by using alkyl benzenes and benzoic acid derivatives as test analytes. The use of these polymers leads to increased retention and separation efficiency compared to the parent monolith. The column efficiency reached values of up to 140,000 plates m^?1. The resulting hybrid monolithic columns also exhibited a satisfactory reproducibility with relative standard deviations of ca. 14% (batch-to-batch).

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Graphical abstract Hybrid polymer monoliths containing large amounts of mesoporous silica-particles (MCM-41 or UVM-7) were prepared by UV initiation. The prepared monolithic columns showed higher retention times and efficiencies than parent monoliths for alkyl benzenes and benzoic acid derivatives.

     

Sample pre-treatment methods for the trace elements determination in seafood products by atomic absorption spectrometry

Different sample pre-treatments for seafood products have been compared with determine trace elements (As, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Se and Zn) by flame atomic absorption spectrometry (FAAS) and electrothermal atomic absorption spectrometry (ETAAS). Classic pre-treatments as microwave assisted-acid digestion and the slurry sampling technique were compared with new procedures such as microwave energy or ultrasound energy assisted-acid leaching process and enzymatic hydrolysis methodologies based on the use of pronase E. The methods were applied to DORM-1 and DOLT-1 reference materials with certified contents for the studied elements. The Student-Newman-Keuls (SNK) method was used to compare with element concentration means obtained with each sample pre-treatment and also the certified concentration means in both reference materials. Multivariate techniques such as principal components analysis (PCA) was also applied to comparative purposes.     

Capillary zone electrophoresis of metal-binding proteins in formic acid with UV- and mass spectrometric detection using cationic transient capillary isotachophoresis for preconcentration

A capillary zone electrophoresis (CZE) method with preceding cationic transient capillary isotachophoresis (tCITP-CZE) was developed for uncoated fused-silica capillaries to analyze metal-binding proteins (MBPs) of clinical relevance. UV detection was followed by mass spectrometry (MS). Optimization was done with model proteins of properties similar to relevant human MBPs. Using 1.0 mol x L(-1) formic acid (pH 1.78) as electrolyte resulted in up to 165000 plates m(-1) in CZE and 230000 plates m(-1) in combination with tCITP and analysis time was less than 5 min in uncoupled mode. Cationic tCITP with 125 mmol x L(-1) ammonium formate, buffered to pH 4.00, as leading electrolyte improved sample loadability considerably in comparison with sample stacking without impairing resolution. Following systematic optimization of the electrospray ionization process (ESI) the coupled system ((tCITP)-CZE-UV-ESI-MS) was tested with protein model mixtures and human MBPs. Repeatability of migration times was < 0.64% in pure CZE mode and in tCITP-CZE mode and < 0.83% in CZE-ESI-MS coupled mode. Mass accuracy was < 0.015%. Limits of detection were found to be in the range 50-160 fmol.     

Determination of quinolones and fluoroquinolones in hospital sewage water by off-line and on-line solid-phase extraction procedures coupled to HPLC-UV

In this work, the development of two solid-phase extraction procedures (off-line and on-line formats) for the identification and quantification of several (fluoro)quinolones in hospital sewage water by HPLC-UV is described. Both procedures are based on the use of C18 and anion exchange (SAX) sorbents for the preconcentration and clean-up steps, respectively, and all variables influencing both steps were optimised. In the off-line format, after its pH was adjusted to 2.5, sample was preconcentrated on a C18 cartridge and eluted with 4 mL of methanol/ammonia (94/6). The methanolic extract must be diluted up to 10 mL with water to allow quantitative retention of the analytes on the SAX cartridge. In the on-line format, the addition of 2.5% of NH4Cl to the sewage water sample (pH = 2.5) was necessary to increase the breakthrough volumes of the analytes in the C18 precolumn. Quantitative transfer of the (fluoro)quinolones from the C18 precolumn to the SAX precolumn was accomplished by pumping 2 mL of a mixture methanol/water (40/60, pH = 9.2) at 2 mL min(-1). Elution of the analytes from the SAX precolumn by means of the chromatographic mobile phase required the inclusion of an additional isocratic step at the beginning of the gradient program. Both off-line and on-line solid phase extraction procedures coupled to HPLC-UV were applied to the analysis of a sewage water sample collected in the sewer system at the output of the St Dimphna Hospital (Geel, Belgium). The fluoroquinolone ciprofloxacin was found in this sample and quantified at 5.8 +/- 0.4 microg L(-1) (off-line method) and 5.6 +/- 0.5 microg L(-1) (on-line method). The analysis of spiked samples containing the seven (fluoro)quinolones studied provided quantitative recoveries in all cases with low RSD values (from 6 to 12%), and all the analytes could be identified by means of their UV spectra with match factors varying from 950 to 985 depending on the (fluoro)quinolone.     

Crystal and molecular structure of cesium hydrogen malonate

The title compound is C₃H₃O₄Cs, CsHM, monoclinic,P2₁/c,a=8.393 (3),b=7.960(2),c=9.023(2) Å,=92.11(2)°. The structure was solved by the heavy-atom method and refined by least-squares techniques to anR factor of 0.023 for 760 observed reflections. The CsHM has no internal symmetry and one carboxy group, but not the other, is twisted almost at right angles (96°) to the plane of the three central carbon atoms. The hydrogen malonate anions are linked together by two short and symmetrical O-HO hydrogen bonds [2.468(4) and 2.482(4) Å]. The structure consists of hydrogen malonate chains cross-linked by the Cs⁺ ion. The IR spectrum of CsHM has been analyzed.     

Finite element LES and VMS methods on tetrahedral meshes

Finite element methods for problems given in complex domains are often based on tetrahedral meshes. This paper demonstrates that the so-called rational Large Eddy Simulation model and a projection-based Variational Multiscale method can be extended in a straightforward way to tetrahedral meshes. Numerical studies are performed with an inf-sup stable second order pair of finite elements with discontinuous pressure approximation.     

Cellular Target of a Rhodium Metalloinsertor is the DNA Base Pair Mismatch

Defects in DNA mismatch repair (MMR) are commonly found in various cancers, especially in colorectal cancers. Despite the high prevalence of MMR-deficient cancers, mismatch-targeted therapeutics are limited and diagnostic tools are indirect. Here, we examine the cytotoxic properties of a rhodium metalloinsertor, [Rh(phen)(chrysi)(PPO)]²⁺ ( RhPPO ) in 27 diverse colorectal cancer cell lines. Despite the low frequency of genomic mismatches and the non-covalent nature of the RhPPO -DNA lesion, RhPPO is on average five times more potent than cisplatin. Importantly, the biological target and profile for RhPPO differs from that of cisplatin. A fluorescent metalloinsertor, RhCy3 , was used to demonstrate that the cellular target of RhPPO is the DNA mismatch. RhCy3 represents a direct probe for MMR-deficiency and correlates directly with the cytotoxicity of RhPPO across different cell lines. Overall, our studies clearly indicate that RhPPO and RhCy3 are promising anticancer and diagnostic probes for MMR-deficient cancers, respectively.