| 1. |
- Engström, Emma, et al.
(författare)
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Effects of sample preparation and calibration strategy on accuracy and precision in the multi-elemental analysis of soil by sector field ICP-MS
- 2004
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Ingår i: Journal of Analytical Atomic Spectrometry. - : Royal Society of Chemistry (RSC). - 0267-9477 .- 1364-5544. ; 19, s. 858-866
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Tidskriftsartikel (refereegranskat)abstract
- Soil samples were prepared for multi-element analysis using HNO3 leaching or pseudo-total digestion with HNO3, HCl and HF in a microwave oven, both methods requiring 70 min heating time. Two calibration approaches for the soil characterization were also compared: external calibration, combined with internal standardization, and isotope dilution (ID) after appropriate spiking of the soils with a stable isotope mixture prior to sample preparation. Analyses were performed using inductively coupled plasma sector field mass spectrometry (ICP-SFMS). Accurate total elemental concentrations were only obtained for Cd and P using both sample preparation methods in two certified reference materials, NIST SRM 2709 and CCRMP SO-2, as well as comparable values for a Finnish inter-laboratory soil. The pseudo-total digestion method also provided accurate results for As, Be, Co, Fe, Mn, Ni, Pb, Sb, Ti, V and Zn. For Cu in SO-2 and Cr in both certified reference materials, incomplete recoveries were always obtained. In the case of Cr, this is due to difficulties associated with the complete solubilization of refractory minerals.For a given final dilution factor, external calibration provides better limits of detection (LODs) than ID. As both methods of quantification yield results of essentially equivalent accuracy and precision, external calibration is to be preferred as a greater number of elements are amenable to analysis in a shorter measurement time. On the other hand, ID can be combined with matrix separation (NH3 precipitation was used here), allowing lower dilution factors to be used without deleterious effects on the instrumental performance. In particular, improved LODs could be obtained for Cd, Cu and Hg, primarily as a result of being able to introduce ten-fold more concentrated solutions from which the bulk of the matrix had been removed. For Cu and Ni, matrix separation almost eliminated Ti, and thus the formation of spectrally interfering TiO+ was completely suppressed. Potentially, the combination of ID and matrix separation would allow these elements to be determined without resorting to medium resolution measurement mode, again improving the LODs for the determination by ID-ICP-SFMS.
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| 2. |
- Engström, Emma, et al.
(författare)
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Multi-elemental characterization of soft biological tissues by inductively coupled plasma-sector field mass spectrometry
- 2004
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Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670 .- 1873-4324. ; 521:2, s. 123-135
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Tidskriftsartikel (refereegranskat)abstract
- The performance of double-focusing, sector field ICP-MS (ICP-SFMS) for the multi-elmental analysis of soft tissues following microwave-assisted digestion with nitric acid was eveluated and factors affecting method limits of detection discussed. Accuracy was assessed by replicate analyses of certified reference materials and by participation in performance evaluation programs; the precision was better than 5% relative standard deviation (RSD) for the majority of elements. Cl was the only element for which ICP-SFMS data consistently deviated from certified concentrations in the reference materials tested. Comparison between results obtained by ICP-SFMS and ICP optical emission spectrometry showed good agreement for elements present in tissues at concentrations above 2 μg g-1. The concentrations of 68 elements in different fish and animal soft tissues (muscle, liver, kidney, lung and brain) are presented, and, where possible, compared to previously published data.
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| 3. |
- Merclin, Nadia, et al.
(författare)
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Transdermal delivery from a lipid sponge phase—iontophoretic and passive transport in vitro of 5-aminolevulinic acid and its methyl ester
- 2004
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Ingår i: Journal of Controlled Release. - : Elsevier BV. - 0168-3659 .- 1873-4995. ; 100:2, s. 191-198
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Tidskriftsartikel (refereegranskat)abstract
- The hydrochloride salts of 5-aminolevulinic acid (ALA) and its methyl ester (m-ALA), respectively, were dissolved in a lipid sponge phase comprising monoolein, propylene glycol and aqueous buffer at concentrations of approximately 0.25% and 16% w/w m-ALA. The iontophoretic and passive delivery of ALA and m-ALA from this formulation through porcine skin in vitro were measured and compared to formulations used in clinical practice, 20% w/w ALA in Unguentum M and Metvix(R) (a cream containing 16% w/w m-ALA). A sponge phase with 16% w/w m-ALA showed a higher passive flux (approximately 140 nmol cm(-2) h(-1) at 5 h) but a lower iontophoretic flux (approximately 800 nmol cm(-2) h(-1) at 5 h) compared to the clinically used products but the differences are hardly significant due to large standard deviations. ALA and m-ALA in sponge phase formulation showed iontophoretic fluxes in the range 80-100 nmol cm(-2) h(-1) at 3 h, i.e. values comparable to the passive fluxes from the more concentrated vehicles. The results demonstrate that the lipid sponge phase, a thermodynamically stable liquid with amphiphilic character, may have potential as a transdermal drug delivery vehicle.
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| 4. |
- Rodushkin, Ilya, et al.
(författare)
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Determination of low-abundant elements at ultra-trace levels in urine and serum by inductively coupled plasma mass spectrometry
- 2004
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Ingår i: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 380:2, s. 247-257
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Tidskriftsartikel (refereegranskat)abstract
- A procedure is described for the determination of Y, Zr, Nb, Ru, Rh, Pd, Ag, SB, Te, Hf, Ta, W, Re, Os, Ir, Pt, An, Tl, Bi, and U in human urine and serum at concentrations relevant to the occupationally unexposed population. Sample preparation was limited to tenfold dilution with 2% HCl. A combination of a sample introduction system designed to provide enhanced sensitivity and the use of water and acids of high-purity has resulted in limits of quantification (LOQ) in the sub-nanogram per liter range for 13 analytes. Instrumental background caused by release of analytes (Y, Zr, Ag, Sb, Au, Tl, Bi, U) from different parts of the sample-introduction system was found to be the major limitation in obtaining better LOQ. Nevertheless, detection capabilities of the proposed procedure were adequate for all elements except Ru, Pd, and Rh. Despite the use of high-resolution mode for these analytes some unresolved spectral interferences might still be present. For 13 elements an external accuracy assessment was accomplished by participating in proficiency testing and inter-comparison programs. Results obtained for pooled urine and serum were compared with concentrations reported for occupationelly unexposed populations in recent publications.
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| 5. |
- Sparr, Emma, et al.
(författare)
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The effect of bacteriorhodopsin, detergent and hydration on the cubic-to-lamellar phase transition in the monoolein-distearoyl phosphatidyl glycerol-water system
- 2004
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736 .- 0006-3002 .- 1878-2434. ; 1665:1-2, s. 156-166
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Tidskriftsartikel (refereegranskat)abstract
- The cubic phase of monoolein (MO) has successfully been used for crystallization of membrane proteins. It is likely that the transition to a lamellar phase upon dehydration is important for the crystallization process, and that the internal dimensions of the lipid phases (i.e., water pore diameter) are crucial for the inclusion and the diffusion of membrane proteins. In the present study, we investigated the cubic-to-lamellar phase transitions in the MO-water and the MO-distearoyl phosphatidyl glycerol (DSPG) systems. The MO-water system was investigated by means of isothermal sorption and desorption microcalorimetry. We show that the transition from cubic to lamellar phase induced by desorption is driven by entropy. At 25 degreesC, this occurs at a water activity of 0.98 with a transition enthalpy of 860 J/mol (MO). The phase behavior was also investigated in the presence of a small amount of the transmembrane protein bacteriorhodopsin (bR), and a detergent, octyl glucoside (OG), and it was shown that both bR and OG stabilize the lamellar phase. Analogous results were obtained for the MO-DSPG-water system. The latter system resembles the MO-water system in that a cubic-to-lamellar phase transition is induced by dehydration, although the structural properties of these phases are slightly different. Finally, we demonstrate that bR can be crystallized from a cubic phase of MO-DSPG-buffer. (C) 2004 Elsevier B.V. All rights reserved.
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| 6. |
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| 7. |
- Stenberg, Anna, et al.
(författare)
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Isotopic variations of Zn in biological materials
- 2004
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 76:14, s. 3971-3978
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Tidskriftsartikel (refereegranskat)abstract
- Variations in the isotopic composition of Zn present in various biological materials were determined using high-resolution multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), following digestion and purification by anion exchange chromatography. To correct for differences in instrumental mass discrimination effects between samples and standards, Cu was employed as an elemental spike. Complementary analyses of Zn separates by sector field ICPMS instruments revealed that the concentrations of the majority of potentially interfering elements were reduced to negligible levels. Residual spectral interferences resulting from 35Cl16O2+, 40Ar14N2+, and 40Ar14N16O+ could be instrumentally resolved from the 67Zn, 68Zn, and 70Zn ion beams, respectively, during measurement by MC-ICPMS. The only other observed interference in the Cu and Zn mass range that could not be effectively eliminated by high-resolution multicollection resulted from 35Cl2+, necessitating modification of the sample preparation procedure to allow accurate 70Zn detection. Complete duplication of the entire analytical procedure for human whole blood and hair, as well as bovine liver and muscle, provided an external reproducibility of 0.05-0.12” (2) for measured 66/64Zn, 67/64Zn, and 68/64Zn values, demonstrating the utility of the method for the precise isotopic analysis of Zn in biological materials. Relative to the selected Zn isotopic standard, 66/64Zn values for biological samples varied from -0.60” in human hair to +0.56” in human whole blood, identifying the former material as the isotopically lightest Zn source found in nature to date.
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