Tobias Jonsson
Umeå University
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Featured researches published by Tobias Jonsson.
Journal of Chromatography A | 2013
Ngoc Phuoc Dinh; Tobias Jonsson; Knut Irgum
Since water associated with the stationary phase surface appears to be the essence of the retention mechanism in hydrophilic interaction chromatography (HILIC), we developed a method to characterize the water-absorbing capabilities of twelve different HILIC stationary phases. Adsorption isotherms for non-modified and monomerically functionalized silica phases adhered to a pattern of monolayer formation followed by multilayer adsorption, whereas water uptake on polymerically functionalized silica stationary phases showed the characteristics of formation and swelling of hydrogels. Water accumulation was affected by adding ammonium acetate as buffer electrolyte and by replacing 5% of the acetonitrile with tertiary solvents capable of hydrogen bonding such as methanol or tetrahydrofuran. The relationship between water uptake and retention mechanism was investigated by studying the correlations between retention factors of neutral analytes and the phase ratios of HILIC columns, calculated either from the surface area (adsorption) or the volume of the water layer enriched from the acetonitrile/water eluent (partitioning). These studies made it evident that adsorption and partitioning actually coexist as retention promoters for neutral solutes in the water concentration regime normally encountered in HILIC. Which factors that dominates is dependent on the nature of the solute, the stationary phase, and the eluting conditions.
Journal of Separation Science | 2008
Patrik Appelblad; Tobias Jonsson; Wen Jiang; Knut Irgum
Separation science is an art of obtaining adequate resolution of the desired compounds in minimum time, and with minimum effort in terms of sample preparation and data evaluation. In LC, where selectivity is a main driving force for separation, the availability of different separation modes capable of operating at high flow rates is a way to make combined optimal use of selectivity, efficiency, and speed. The separation of polar and hydrophilic compounds is problematic in RP LC due to the poor retention. Hydrophilic interaction liquid chromatography (HILIC) is a more straightforward separation mode to address this problem. Herein, it is shown that separations in HILIC mode are equally efficient as for RP, providing a potential for very fast separations on short columns. This is not only facilitated by the low viscosity of the mobile phase compositions used, compared to typical RP eluents, but also due to higher column permeability. To exemplify this, baseline separations of uracil and cytosine are shown in less than 4 s and of Tamiflu and its main metabolite in less than 40 s, both under isocratic conditions. HILIC must therefore be considered having potential for high throughput purposes, and being an attractive candidate as the second separation dimension in 2-D HPLC.
Journal of Chromatography A | 2011
Erika Wikberg; Tobias Sparrman; Camilla Viklund; Tobias Jonsson; Knut Irgum
2H NMR has been used as a tool for probing the state of water in hydrophilic stationary phases for liquid chromatography at temperatures between -80 and +4 °C. The fraction of water that remained unfrozen in four different neat silicas with nominal pore sizes between 60 and 300 Å, and in silicas with polymeric sulfobetaine zwitterionic functionalities prepared in different ways, could be determined by measurements of the line widths and temperature-corrected integrals of the 2H signals. The phase transitions detected during thawing made it possible to estimate the amount of non-freezable water in each phase. A distinct difference was seen between the neat and modified silicas tested. For the neat silicas, the relationship between the freezing point depression and their pore size followed the expected Gibbs-Thomson relationship. The polymeric stationary phases were found to contain considerably higher amounts of non-freezable water compared to the neat silica, which is attributed to the structural effect that the sulfobetaine polymers have on the water layer close to the stationary phase surface. The sulfobetaine stationary phases were used alongside the 100 Å silica to separate a number of polar compounds in hydrophilic interaction (HILIC) mode, and the retention characteristics could be explained in terms of the surface water structure, as well as by the porous properties of the stationary phases. This provides solid evidence supporting a partitioning mechanism, or at least of the existence of an immobilized layer of water into which partitioning could be occurring.
Analytica Chimica Acta | 1998
Tobias Jonsson; Malin Emteborg; Knut Irgum
Substituted imidazoles and leaving groups known from other areas of chemistry have been tested for catalytic efficiency in the peroxyoxalate chemiluminescence (PO-CL) reaction, using bis(2,4,6-tric ...
Analytica Chimica Acta | 1999
Tobias Jonsson; Knut Irgum
Peroxyoxalate chemiluminescence (PO-CL) detection offers an advantage in chromatographic detection, by the virtue of its multiple unique selectivities and high sensitivity. However, many of the analytical separation techniques available today require observation times in the millisecond range to preserve the band resolution, and as the reaction kinetics of the PO-CL reaction is considerably slower, extra flow elements are needed to observe the reaction in a time window at maximum emission intensity. Since these flow elements increase the complexity of the system and contribute to band-broadening, the rational way to adapt PO-CL detection to miniaturised separation systems is to speed up the reaction, so that it emits an initial burst of light within the acceptable detection time-frame. Although this may result in a lower overall quantum yield, the actual detection sensitivity could be equal to, or better than slower PO-CL systems. By making careful selections of oxalic reagent and catalyst(s) the reaction can be fine-tuned to maximise the intensity. In this work, the time-dependent light emission from the reaction of bis(2,4,6-trichlorophenyl)oxalate (TCPO) was studied under the catalytic influence of imidazole, 1,2,4-triazole, 4-dimethylaminopyridine (DMAP), and 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) in acetonitrile. Both DMAP and DBU accelerated the reaction substantially, but the best combination of reaction speed and intensity was found for a mixture of 0.5 mM DBU and 5 mM 1,2,4-triazole, which reached its maximum emission after only 40 ms and had an emission intensity comparable to that seen with 5 mM imidazole as catalyst.
Journal of Analytical Atomic Spectrometry | 2002
Erik Björn; Tobias Jonsson; Daniel Goitom
Noise power spectra and analytical precision data were generated and compared for a direct injection high efficiency nebuliser, DIHEN, and a micro concentric nebuliser, MCN, combined with a double pass or cyclone spray chamber for sample introduction in inductively coupled plasma mass spectrometry, ICP-MS. The different systems were compared using liquid flow rates of 85 or 100 µL min−1. Steady-state signals for 115In+ and steady-state isotope ratio measurements for 107Ag+/109Ag+ were chosen for the investigation. For background and shot noise limited precision the DIHEN was found to give better precision than the double pass spray chamber system due to higher sensitivity. For flicker noise limited precision it was found that white noise and pump interference noise were higher, and 1/f noise and mains power interference noise were lower, for the DIHEN compared to the spray chamber systems. As a result of this, for 115In+ measurements, the DIHEN gave 2–9 times higher relative standard deviation, RSD, at measurement frequencies above 1 Hz but slightly lower RSD (not statistically significant) at frequencies below 0.1 Hz compared to the conventional systems. For the isotope ratio measurements, due to the high white noise level, the DIHEN generally gave poorer precision compared to the double pass spray chamber system. To convincingly explain the rationale for the observed flicker noise limited precision data, the effect of different noise components on analytical precision was evaluated. This study made obvious the relationship between precision and different noise components visualised in noise power spectra. Such information is useful for rational optimisation of operating conditions and technical developments of instrumentation. The mathematical simulation procedure used for this study was also applied to experimental data to predict analytical precision at typical measurement frequencies.
Journal of Separation Science | 2013
Giorgio Marrubini; Alice Pedrali; Petrus Hemström; Tobias Jonsson; Patrik Appelblad; Gabriella Massolini
Short-chain carboxylic acids are relevant in pharmaceutical, food quality control, and biomedical analysis. In this study, 11 acids commonly found in drugs and in food products were selected. Wine was chosen as matrix for testing the method. The test compounds were used for comparing the selectivity of four 150 × 2.1 mm zwitterionic hydrophilic interaction LC (HILIC) columns (ZIC-HILIC 5 μm, 200 Å, and 3.5 μm, 100 Å, ZIC-pHILIC 5 μm, ZIC-cHILIC 3 μm, 100 Å) while varying the conditions to optimize for low UV wavelength detection and achieve high sensitivity. Retention using potassium phosphate and ammonium carbonate as mobile-phase components at pH 6.0, 7.5, and 8.5-8.9 was studied considering recent hypotheses on HILIC mechanism-related with the Hofmeister series effect and ion hydration. An isocratic method with UV detection at 200 nm and mobile phase consisting of 75% acetonitrile and 10 mM potassium phosphate at pH 6.0 applied to a ZIC-cHILIC column was found provisionally optimal and partially validated for the 11 analytes. Satisfactory results (R(2) from 0.9940 to >0.9999), and recoveries from 93-106% for all analytes evidenced the method as suitable for wine analysis. To the best of our knowledge, no previous study has reported on the direct ZIC-HILIC separation and UV detection of the acids considered here in wine.
Journal of Analytical Atomic Spectrometry | 2002
Erik Björn; Tobias Jonsson; Daniel Goitom
Peristaltic pump interference noise and corresponding harmonics were investigated for inductively coupled plasma mass spectrometry, ICP-MS, by means of noise power spectra, NPS, and analytical precision data for 115In+ and 38Ar+ measurements. A direct injection high efficiency nebuliser, DIHEN, and a micro concentric nebuliser, MCN, combined with a double pass or cyclone spray chamber were used for sample introduction. It was found that for the DIHEN the harmonics of the fundamental pump frequency originated from the liquid flow pattern of the pump and the non-linear relation between analyte signal intensity and liquid flow rate. For the spray chamber systems it was found that, under the experimental conditions used here, the harmonics mainly originated from the pulsations in the draining of the spray chamber. The operating frequency of the draining pump also had an influence on analytical precision such that a low frequency (1/3 Hz) of the draining pump was favourable for high measurement frequencies and a higher draining pump frequency (4 Hz) was favourable for low measurement frequencies.
Computer Methods in Applied Mechanics and Engineering | 2017
Peter Hansbo; Tobias Jonsson; Mats G. Larson; Karl Larsson
We develop a finite element method for elliptic partial differential equations on so called composite surfaces that are built up out of a finite number of surfaces with boundaries that fit together ...
Journal of Pharmaceutical and Biomedical Analysis | 2015
Alice Pedrali; Mariella Bleve; Priscilla Capra; Tobias Jonsson; Gabriella Massolini; Paola Perugini; Giorgio Marrubini
N-Acetylglucosamine is an ingredient in pharmaceuticals, nutritional supplements and in cosmetics. N-Acetylglucosamine in cosmetics is expected to improve skin hydration, reparation, and to contribute as anti-wrinkle agent. This study reports on the validation and application of an HPLC method based on HILIC and UV detection for determining N-acetylglucosamine in cosmetics and in samples obtained after testing the skin exposed to cosmetics formulations. The chromatographic column used is a ZIC(®)-pHILIC (150 mm × 4.6 mm, 5 μm particle size) on which a mobile phase containing acetonitrile-aqueous KH2PO4 (70:30, v/v) 15 mM was applied in isocratic elution mode injecting 20 μl of sample at 0.5 ml/min constant flow-rate and 10±1°C column temperature. Under these conditions the total run time was 10 min and N-acetylglucosamine eluted baseline separated from all other compounds in the samples. Calibration in the range from 40 to 80 μg/ml allowed to assess the method linearity (R(2)>0.999) in a concentration range corresponding to about 50% to 120% of the expected levels of N-acetylglucosamine in the formulations. Precision expressed by RSD% was always better than 2% in intra-day and inter-day assays of authentic samples. Accuracy was in all cases within 95-105% of the expected concentration value in formulations containing N-acetylglucosamine. The sensitivity of the method was at the level of 10 μg/ml as limit of detection, and at 40 μg/ml as limit of quantitation. The application of the method to formulations containing solid lipid nanoparticles documents its usefulness in cosmetic quality control. The results witness that the method is also suitable for the determination of N-acetylglucosamine in samples obtained from skin test strips.