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  • 1.
    Alleso, Morten
    et al.
    Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, and Department of Food Science, Faculty of Life Sciences, University of Copenhagen.
    Velaga, Sitaram
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Alhalaweh, Amjad
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Medicinsk vetenskap.
    Cornett, Claus
    Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, and Department of Food Science, Faculty of Life Sciences, University of Copenhagen.
    Rasmussen, Morten A.
    Department of Food Science, Faculty of Life Sciences, University of Copenhagen.
    Berg, Frans van den
    Department of Food Science, Faculty of Life Sciences, University of Copenhagen.
    Diego, Heidi Lopez de
    Analytical R and D, H. Lundbeck A/S.
    Rantanen, Jukka
    Department of Pharmaceutics and Analytical Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen.
    Near-infrared spectroscopy for cocrystal screening: a comparative study with Raman spectroscopy2008Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 80, nr 20, s. 7755-7764Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Near-infrared (NIR) spectroscopy is a well-established technique for solid-state analysis, providing fast, noninvasive measurements. The use of NIR spectroscopy for polymorph screening and the associated advantages have recently been demonstrated. The objective of this work was to evaluate the analytical potential of NIR spectroscopy for cocrystal screening using Raman spectroscopy as a comparative method. Indomethacin was used as the parent molecule, while saccharin and L-aspartic acid were chosen as guest molecules. Molar ratios of 1:1 for each system were subjected to two types of preparative methods. In the case of saccharin, liquid-assisted cogrinding as well as cocrystallization from solution resulted in a stable 1:1 cocrystalline phase termed IND-SAC cocrystal. For L-aspartic acid, the solution-based method resulted in a polymorphic transition of indomethacin into the metastable a form retained in a physical mixture with the guest molecule, while liquid-assisted cogrinding did not induce any changes in the crystal lattice. The good chemical peak selectivity of Raman spectroscopy allowed a straightforward interpretation of sample data by analyzing peak positions and comparing to those of pure references. In addition, Raman spectroscopy provided additional information on the crystal structure of the IND-SAC cocrystal. The broad spectral line shapes of NIR spectra make visual interpretation of the spectra difficult, and consequently, multivariate modeling by principal component analysis (PCA) was applied. Successful use of NIR/PCA was possible only through the inclusion of a set of reference mixtures of parent and guest molecules representing possible solid-state outcomes from the cocrystal screening. The practical hurdle related to the need for reference mixtures seems to restrict the applicability of NIR spectroscopy in cocrystal screening.

  • 2. Appelblad, P.K.
    et al.
    Rodushkin, Ilia
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Baxter, Douglas
    Sources of uncertainty in isotope ratio measurements by inductively coupled plasma mass spectrometry2001Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 73, nr 13, s. 2911-2919Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A model is presented describing the effects of dead time and mass bias correction factor uncertainties, flicker noise, and counting statistics on isotope ratio measurement precision using inductively coupled plasma mass spectrometry (ICPMS) with a single collector. Noise spectral analysis is exploited to enable estimation of the flicker noise parameters. For the instrument used, the flicker noise component exhibited a fairly weak frequency (f) dependence ( f -0.33±0.12), but was directly proportional to the total number of counts, Q. As white noise, determined by counting statistics, is given by Q0.5, the isotope ratio measurement uncertainties will actually cease to improve when Q exceeds a certain threshold. This would suggest that flicker noise could become the limiting factor for the precision with which isotope ratios can be determined by ICPMS. However, under most experimental conditions, uncertainties associated with mass discrimination and dead time correction factors are decisive. For ratios up to ~22 (115In/113In), optimum major isotope count rates are generally below 0.3 MHz, for which precision in the mass discrimination factor is limiting. The model derived could be used as a starting point for determining optimum conditions and understanding the limitations of single-collector ICPMS for precise isotope ratio measurements.

  • 3. Burman, Jan-Ola
    et al.
    Boström, Kurt
    Luleå tekniska universitet.
    Comparison of different plasma excitation and calibration methods in the analysis of geological materials by optical emission spectrometry1979Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 51, nr 4, s. 516-520Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A comparative study has been made of different dissolution and calibration methods for analyses by optical emission spectrometry (OES) utilizing inductively coupled plasma (ICP) and capacitively coupled microwave plasma (MWP) as excitation sources. The test substances were geological standard rocks, in which SlO2, Al2O3, TiO2, Fe2O3, MnO, MgO CaO, Na2O, Ba, and some traces were determined. The results show that analyses by MWP-OES are severely disturbed by matrix effects; only in the presence of large quantities of ionization buffers e.g., [Sr(NO3)2] can MWP-OES yield rock analyses of very good quality. No buffers are needed for analyses by ICP-OES, for which the matrix effects are remarkably low. ICP-OES may suffer from annoying nebulizer disturbances when concentrated solutions are used but, with properly diluted solutions, all major and many trace elements can routinely be analyzed in 50-mg rock samples. MWP-OES on the other hand is poorly suited for trace element determinationsA comparative study has been made of different dissolution and calibration methods for analyses by optical emission spectrometry (OES) utilizing inductively coupled plasma (ICP) and capacitively coupled microwave plasma (MWP) as excitation sources. The test substances were geological standard rocks, in which SlO2, Al2O3, TiO2, Fe2O3, MnO, MgO CaO, Na2O, Ba, and some traces were determined. The results show that analyses by MWP-OES are severely disturbed by matrix effects; only in the presence of large quantities of ionization buffers e.g., [Sr(NO3)2] can MWP-OES yield rock analyses of very good quality. No buffers are needed for analyses by ICP-OES, for which the matrix effects are remarkably low. ICP-OES may suffer from annoying nebulizer disturbances when concentrated solutions are used but, with properly diluted solutions, all major and many trace elements can routinely be analyzed in 50-mg rock samples. MWP-OES on the other hand is poorly suited for trace element determinations. © 1979 American Chemical Society.

  • 4. Burman, Jan-Ola
    et al.
    Ponter, Christer
    Luleå tekniska universitet.
    Boströn, Kurt
    Luleå tekniska universitet.
    Metaborate digestion procedure for inductively coupled plasma-optical emission spectrometry1978Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 50, nr 4, s. 679-680Artikkel i tidsskrift (Fagfellevurdert)
  • 5.
    Dunuwila, Dilum D.
    et al.
    Michigan State University.
    Torgerson, B. A.
    Michigan State University.
    Chang, C. K.
    Michigan State University.
    Berglund, Kris
    Sol-gel derived titanium carboxylate thin films for optical detection of analytes1994Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 66, nr 17, s. 2739-2744Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The feasibility of using a sol-gel derived titanium carboxylate thin film, which can be supported on glass, for the fabrication of optical test strips was investigated using a model probe/ analyte combination. The porous films, being optically transparent and baring the capability to host probe molecules, provided an excellent system to investigate the possibility of making optical test strips. A colorimetric reagent, an iron(III) porpohyrin, was chosen as the probe molecule to detect free cyanide ion concentrations in aqueous solutions. Entrapment of the porphyrin in the film was accomplished by direct dissolution of the porphyrin in the sol-gel solutions. Chemically induced structural modifications of the polymer were carried out to stabilize the encapsulated metalloporphyrin within the sol-gel derived matrix. The syntheses of this model analyte detection system and its response are presented. An optical parameter reflective of the chemical changes that occur in the system was selected as the measurement tool; its response asymptotically increased over the cyanide ion concentration range of 40-25 000 ppm.

  • 6.
    Engström, Emma
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Rodushkin, Ilya
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Baxter, Douglas
    Öhlander, Björn
    Chromatographic purification for the determination of dissolved silicon isotopic composition in natural waters by high-resolution multicollector inductively coupled plasma mass spectrometry2006Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 78, nr 1, s. 250-257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A procedure is described for accurate Si isotope ratio measurements by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Dissolved silicon was preconcentrated and separated from other elements present in natural surface waters using anion-exchange chromatography. The optimized procedure provides virtually complete elimination of major inorganic constituents while maintaining Si recovery in excess of 97%. High-resolution capabilities of MC-ICPMS used in this study allow interference-free measurements of 28Si and 29Si isotopes using conventional solution nebulization sample introduction without aerosol desolvation. Owing to the magnitude of polyatomic ion contributions in the region of mass 30, mostly from 14N16O+, measurements of the 30Si isotope can be affected by tailing of the interference signals, making exact matching of analyte and nitric acid concentrations in all measurement solutions mandatory. Isotope abundance ratio measurements were performed using the bracketing standards approach and on-line correction for mass-bias variations using an internal standard (Mg). Uncertainties, expressed as 95% confidence intervals, for replication of the entire procedure are better than ±0.18" for δ29Si and ±0.5" for δ30Si. For the first time with MC-ICPMS, the quality of Si isotope abundance ratio measurements could be verified using a three-isotope plot. All samples studied were isotopically heavier than the IRMM-018 Si isotopic reference material.

  • 7.
    Rodushkin, Ilia
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stenberg, Anna
    Andren, Henrik
    Malinovskiy, Dmitry
    Baxter, Douglas
    Isotopic fractionation during diffusion of transition metal ions in solution2004Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 76, nr 7, s. 2148-2151Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Isotope ratios and elemental concentrations were measured in aqueous solutions sampled at varying distances from sources of Fe or Zn ions. The measurements reveal fractionation of isotopes resulting from pure diffusion in solution. Our data demonstrate that diffusion alone can cause changes in 56Fe/54Fe and 66Zn/64Zn isotope ratios in excess of -0.3”. These findings thus confirm previous suspicions that transport processes contribute to observed variations in isotopic compositions. Diffusion must therefore be considered when attempting to make inferences from isotope measurements on samples originating from aqueous systems where concentration gradients may develop.

  • 8.
    Stenberg, Anna
    et al.
    Luleå tekniska universitet.
    Andren, Henrik
    Malinovskiy, Dmitry
    Engström, Emma
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Rodushkin, Ilia
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Baxter, Douglas
    Isotopic variations of Zn in biological materials2004Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 76, nr 14, s. 3971-3978Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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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