Tobias Jonsson | Umeå University (original) (raw)

Papers by Tobias Jonsson

Research paper thumbnail of Accumlations of ammonium acetate on polar materials under HILIC condition and its relation to retention of analytes

Research paper thumbnail of Probing the interaction mode in hydrophilic interaction chromatography

Journal of Chromatography A, 2011

This work aims at characterizing interactions between a select set of probes and 22 hydrophilic a... more This work aims at characterizing interactions between a select set of probes and 22 hydrophilic and polar commercial stationary phases, to develop an understanding of the relationship between the chemical properties of those phases and their interplay with the eluent and solutes in hydrophilic interaction chromatography. "Hydrophilic interaction" is a somewhat inexact term, and an attempt was therefore made to characterize the interactions involved in HILIC as hydrophilic, hydrophobic, electrostatic, hydrogen bonding, dipole-dipole,interaction, and shape-selectivity. Each specific interaction was quantified from the separation factors of a pair of similar substances of which one had properties promoting the interaction mode being probed while the other did not. The effects of particle size and pore size of the phases on retention and selectivity were also studied. The phases investigated covered a wide range of surface functional groups including zwitterionic (sulfobetaine and phosphocholine), neutral (amide and hydroxyl), cationic (amine), and anionic (sulfonic acid and silanol). Principal component analysis of the data showed that partitioning was a dominating mechanism for uncharged solutes in HILIC. However, correlations between functional groups and interactions were also observed, which confirms that the HILIC retention mechanism is partly contributed by adsorption mechanisms involving electrostatic interaction and multipoint hydrogen bonding. Phases with smaller pore diameters yielded longer retention of solutes, but did not significantly change the column selectivities. The particle diameter had no significant effect, neither on retention, nor on the selectivities. An increased water content in the eluent reduced the multipoint hydrogen bonding interactions, while an increased electrolyte concentration lowered the selectivities of the tested columns and made their interaction patterns more similar.

Research paper thumbnail of Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention

Journal of Chromatography A, 2013

Since water associated with the stationary phase surface appears to be the essence of the retenti... more 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.

Research paper thumbnail of A 2H nuclear magnetic resonance study of the state of water in neat silica and zwitterionic stationary phases and its influence on the chromatographic retention characteristics in hydrophilic interaction high-performance liquid chromatography

Journal of Chromatography A, 2011

2H NMR has been used as a tool for probing the state of water in hydrophilic stationary phases fo... more 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.

Research paper thumbnail of Column comparison and method development for the analysis of short-chain carboxylic acids by zwitterionic hydrophilic interaction liquid chromatography with UV detection

Journal of Separation Science, 2013

Short-chain carboxylic acids are relevant in pharmaceutical, food quality control, and biomedical... more 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.

Research paper thumbnail of Determination of N-acetylglucosamine in cosmetic formulations and skin test samples by hydrophilic interaction liquid chromatography and UV detection

Journal of pharmaceutical and biomedical analysis, Jan 23, 2014

N-Acetylglucosamine is an ingredient in pharmaceuticals, nutritional supplements and in cosmetics... more 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 (150mm×4.6mm, 5μm particle size) on which a mobile phase containing acetonitrile-aqueous KH2PO4 (70:30, v/v) 15mM was applied in isocratic elution mode injecting 20μl of sample at 0.5ml/min constant flow-rate and 10±1°C column temperature. Under these conditions the total run time was 10min and N-acetylglucosamine eluted baseline separated from all other compounds in the samples. Calibration in the range from 40 to 80μg/ml allowed to assess the method linearity (R(2)>0.999) in a c...

Research paper thumbnail of HPLC columns partition by chemometric methods based on peptides retention☆

Journal of Chromatography B, 2007

In recent years, multivariate techniques have been utilized to evaluate reversed-phase high-perfo... more In recent years, multivariate techniques have been utilized to evaluate reversed-phase high-performance liquid chromatographic data. In the present study, 11 high-performance liquid chromatography (HPLC) columns were divided into several groups according to the retention factors of 12 peptides. Principal component analysis (PCA) and cluster analysis (CA) were used in column and peptides' comparison and grouping. CA results indicated that all stationary phases may be generally grouped into several clusters, due to stationary phase structure and properties. On the other hand, interesting results were obtained with the use of PC. There is almost linear relationship between classified HPLC columns in the space of new PCs, which is connected with meaning of the PC's reflected in their loading values. The first component describes non-polar properties of peptides, whereas the second component is loaded with polar peptides having much lower log P values. PCA and CA were also used in peptides comparison however, complete explanation of peptides grouping still remains unclear.

Research paper thumbnail of Comparative evaluation of high-performance liquid chromatography stationary phases used for the separation of peptides in terms of quantitative structure–retention relationships

Journal of Chromatography A, 2007

Chromatographic measurements were made on 17 physicochemically diversified high-performance liqui... more Chromatographic measurements were made on 17 physicochemically diversified high-performance liquid chromatography (HPLC) columns which were further analyzed in terms of their similarities and dissimilarities for 25 carefully designed, structurally diverse peptides showing distinctly distinguished groups. The goal of the study was to investigate the molecular mechanism of retention and to find an objective manner of quantitative comparison of retention properties and classification of modern stationary phases for reverse phase HPLC (RP-HPLC). We utilized the structural descriptors of peptides obtained from molecular modeling to describe their chromatographic retention behavior under given HPLC conditions. Quantitative structure-retention relationships (QSRR) with the following descriptors were employed: logarithm of the sum of amino acid retention contributions in a given peptide, log Sum AA , logarithm of the Van der Waals volume of the peptide, log VDW vol , and logarithm of its calculated n-octanol/water coefficient, clog P. The best QSRR equations were obtained in the case of monolithic and regular octadecylsilica columns. On the other hand, the combination of QSRR and principal component analysis (PCA) can be considered as the efficient tool allowing column classification and searching for orthogonal HPLC conditions required to separate peptides.

Research paper thumbnail of New Nucleophilic Catalysts for Bright and Fast Peroxyoxalate Chemiluminescence

Analytical Chemistry, 2000

Miniaturized detection applications based on chemiluminescence require fast reaction kinetics for... more Miniaturized detection applications based on chemiluminescence require fast reaction kinetics for optimum performance. In this work, high-intensity light from the analytically useful peroxyoxalate chemiluminescence reaction has been generated at high rates by employing both single-component and dual-component nucleophilic catalysis. 4-(Dimethylamino)pyridine and its derivatives were superior to all other bases in terms of reaction speed and intensity of the generated light and outshone imidazole, which hitherto has been considered as the best catalyst. The light intensity was related to the difference in pK a between the 4-aminopyridine catalyst and the leaving group of the reagent, and the optimum ∆pK a was found to be close to 0. Similarly, high light intensities were obtained when mixtures of the imidazole analogue 1,2,4triazole and the strong, nonnucleophilic base 1,2,2,6,6pentamethylpiperidine acted as catalysts. The mechanism behind this was concluded to be a "base-induced nucleophilic catalysis", where the ancillary strong base assisted the production of the highly nucleophilic 1,2,4-triazolate anion, which as the actual catalyst then participated in the formation of a more reactive transient reagent. All the investigated catalysts reduced the light yield of the reaction due to base-catalyzed breakdown reactions of the reagents and/or intermediates. The intensity peak maximums of these bright and fast reactions typically appeared after less than 10 ms, whereafter the light decayed to darkness within a few seconds. These reaction characteristics are especially advantageous for sensitive detection applications where the observation volumes and times are limited, e.g., peaks emerging from a capillarybased separation process.

Research paper thumbnail of Determination of C-21 Ketosteroids in Serum Using Trifluoromethanesulfonic Acid Catalyzed Precolumn Dansylation and 1,1‘-Oxalyldiimidazole Postcolumn Peroxyoxalate Chemiluminescence Detection

Analytical Chemistry, 1998

A new procedure for the quantitation of C-21 ketosteroids using trifluoromethanesulfonic acid-cat... more A new procedure for the quantitation of C-21 ketosteroids using trifluoromethanesulfonic acid-catalyzed precolumn dansylation and coupled column liquid chromatographic separation, followed by postcolumn 1,1′-oxalyldiimidazole peroxyoxalate chemiluminescence detection is presented.

Research paper thumbnail of Heterocyclic compounds as catalysts in the peroxyoxalate chemiluminescence reaction of bis(2,4,6-trichlorophenyl)oxalate

Analytica Chimica Acta, 1998

Substituted imidazoles and leaving groups known from other areas of chemistry have been tested fo... more Substituted imidazoles and leaving groups known from other areas of chemistry have been tested for catalytic ef®ciency in the peroxyoxalate chemiluminescence (PO-CL) reaction, using bis(2,4,6-trichlorophenyl)oxalate (TCPO) as reagent. Catalytic activity was found for 1,2,4-triazole, 1-methylimidazole, 2-methylimidazole, 4-methylimidazole and 4,5-dichloroimidazole, while 2-mercaptoimidazole, 2-nitroimidazole, 4-nitroimidazole, benzimidazole, benzotriazole, thiazole, o-benzoic sul®mide, phthalimide, succinimide, 2(1H)-pyridone and 1,2,3-benzotriazine-4(3H)-one yielded no detectable chemiluminescence under the conditions used. None of the tested compounds was more ef®cient than imidazole in catalyzing the PO-CL reaction. Spectrophotometric measurements of the catalytic breakdown of TCPO showed that an intermediate was formed with almost all catalysts, and that intermediates that were more stable or present at lower concentration led to a reduced catalytic ef®ciency in the PO-CL reaction of TCPO. # 1998 Elsevier Science B.V. 0003-2670/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. P I I S 0 0 0 3 -2 6 7 0 ( 9 8 ) 0 0 0 2 9 -4

Research paper thumbnail of Very fast peroxyoxalate chemiluminescence

Peroxyoxalate chemiluminescence (PO-CL) detection offers an advantage in chromatographic detectio... more 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.

Research paper thumbnail of Noise characteristics and analytical precision of a direct injection high efficiency and micro concentric nebuliser for sample introduction in inductively coupled plasma mass spectrometry

Journal of Analytical Atomic Spectrometry, 2002

ABSTRACT Noise power spectra and analytical precision data were generated and compared for a dire... more ABSTRACT 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.

Research paper thumbnail of The origin of peristaltic pump interference noise harmonics in inductively coupled plasma mass spectrometry

Journal of Analytical Atomic Spectrometry, 2002

... Acta, Part B, 1989, 44, 649 CrossRef Search PubMed . 6, E. Björn, T. Jonsson and D. Goitom, J... more ... Acta, Part B, 1989, 44, 649 CrossRef Search PubMed . 6, E. Björn, T. Jonsson and D. Goitom, J. Anal. At. ... Acta, Part B, 1982, 37, 1075 CrossRef Search PubMed . 10, SO Engblom, JC Myland and KB Oldham, J. Electroanal. Chem., 2000, 480, 120 CrossRef CAS Search PubMed . ...

Research paper thumbnail of Accumlations of ammonium acetate on polar materials under HILIC condition and its relation to retention of analytes

Research paper thumbnail of Probing the interaction mode in hydrophilic interaction chromatography

Journal of Chromatography A, 2011

This work aims at characterizing interactions between a select set of probes and 22 hydrophilic a... more This work aims at characterizing interactions between a select set of probes and 22 hydrophilic and polar commercial stationary phases, to develop an understanding of the relationship between the chemical properties of those phases and their interplay with the eluent and solutes in hydrophilic interaction chromatography. "Hydrophilic interaction" is a somewhat inexact term, and an attempt was therefore made to characterize the interactions involved in HILIC as hydrophilic, hydrophobic, electrostatic, hydrogen bonding, dipole-dipole,interaction, and shape-selectivity. Each specific interaction was quantified from the separation factors of a pair of similar substances of which one had properties promoting the interaction mode being probed while the other did not. The effects of particle size and pore size of the phases on retention and selectivity were also studied. The phases investigated covered a wide range of surface functional groups including zwitterionic (sulfobetaine and phosphocholine), neutral (amide and hydroxyl), cationic (amine), and anionic (sulfonic acid and silanol). Principal component analysis of the data showed that partitioning was a dominating mechanism for uncharged solutes in HILIC. However, correlations between functional groups and interactions were also observed, which confirms that the HILIC retention mechanism is partly contributed by adsorption mechanisms involving electrostatic interaction and multipoint hydrogen bonding. Phases with smaller pore diameters yielded longer retention of solutes, but did not significantly change the column selectivities. The particle diameter had no significant effect, neither on retention, nor on the selectivities. An increased water content in the eluent reduced the multipoint hydrogen bonding interactions, while an increased electrolyte concentration lowered the selectivities of the tested columns and made their interaction patterns more similar.

Research paper thumbnail of Water uptake on polar stationary phases under conditions for hydrophilic interaction chromatography and its relation to solute retention

Journal of Chromatography A, 2013

Since water associated with the stationary phase surface appears to be the essence of the retenti... more 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.

Research paper thumbnail of A 2H nuclear magnetic resonance study of the state of water in neat silica and zwitterionic stationary phases and its influence on the chromatographic retention characteristics in hydrophilic interaction high-performance liquid chromatography

Journal of Chromatography A, 2011

2H NMR has been used as a tool for probing the state of water in hydrophilic stationary phases fo... more 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.

Research paper thumbnail of Column comparison and method development for the analysis of short-chain carboxylic acids by zwitterionic hydrophilic interaction liquid chromatography with UV detection

Journal of Separation Science, 2013

Short-chain carboxylic acids are relevant in pharmaceutical, food quality control, and biomedical... more 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.

Research paper thumbnail of Determination of N-acetylglucosamine in cosmetic formulations and skin test samples by hydrophilic interaction liquid chromatography and UV detection

Journal of pharmaceutical and biomedical analysis, Jan 23, 2014

N-Acetylglucosamine is an ingredient in pharmaceuticals, nutritional supplements and in cosmetics... more 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 (150mm×4.6mm, 5μm particle size) on which a mobile phase containing acetonitrile-aqueous KH2PO4 (70:30, v/v) 15mM was applied in isocratic elution mode injecting 20μl of sample at 0.5ml/min constant flow-rate and 10±1°C column temperature. Under these conditions the total run time was 10min and N-acetylglucosamine eluted baseline separated from all other compounds in the samples. Calibration in the range from 40 to 80μg/ml allowed to assess the method linearity (R(2)>0.999) in a c...

Research paper thumbnail of HPLC columns partition by chemometric methods based on peptides retention☆

Journal of Chromatography B, 2007

In recent years, multivariate techniques have been utilized to evaluate reversed-phase high-perfo... more In recent years, multivariate techniques have been utilized to evaluate reversed-phase high-performance liquid chromatographic data. In the present study, 11 high-performance liquid chromatography (HPLC) columns were divided into several groups according to the retention factors of 12 peptides. Principal component analysis (PCA) and cluster analysis (CA) were used in column and peptides' comparison and grouping. CA results indicated that all stationary phases may be generally grouped into several clusters, due to stationary phase structure and properties. On the other hand, interesting results were obtained with the use of PC. There is almost linear relationship between classified HPLC columns in the space of new PCs, which is connected with meaning of the PC's reflected in their loading values. The first component describes non-polar properties of peptides, whereas the second component is loaded with polar peptides having much lower log P values. PCA and CA were also used in peptides comparison however, complete explanation of peptides grouping still remains unclear.

Research paper thumbnail of Comparative evaluation of high-performance liquid chromatography stationary phases used for the separation of peptides in terms of quantitative structure–retention relationships

Journal of Chromatography A, 2007

Chromatographic measurements were made on 17 physicochemically diversified high-performance liqui... more Chromatographic measurements were made on 17 physicochemically diversified high-performance liquid chromatography (HPLC) columns which were further analyzed in terms of their similarities and dissimilarities for 25 carefully designed, structurally diverse peptides showing distinctly distinguished groups. The goal of the study was to investigate the molecular mechanism of retention and to find an objective manner of quantitative comparison of retention properties and classification of modern stationary phases for reverse phase HPLC (RP-HPLC). We utilized the structural descriptors of peptides obtained from molecular modeling to describe their chromatographic retention behavior under given HPLC conditions. Quantitative structure-retention relationships (QSRR) with the following descriptors were employed: logarithm of the sum of amino acid retention contributions in a given peptide, log Sum AA , logarithm of the Van der Waals volume of the peptide, log VDW vol , and logarithm of its calculated n-octanol/water coefficient, clog P. The best QSRR equations were obtained in the case of monolithic and regular octadecylsilica columns. On the other hand, the combination of QSRR and principal component analysis (PCA) can be considered as the efficient tool allowing column classification and searching for orthogonal HPLC conditions required to separate peptides.

Research paper thumbnail of New Nucleophilic Catalysts for Bright and Fast Peroxyoxalate Chemiluminescence

Analytical Chemistry, 2000

Miniaturized detection applications based on chemiluminescence require fast reaction kinetics for... more Miniaturized detection applications based on chemiluminescence require fast reaction kinetics for optimum performance. In this work, high-intensity light from the analytically useful peroxyoxalate chemiluminescence reaction has been generated at high rates by employing both single-component and dual-component nucleophilic catalysis. 4-(Dimethylamino)pyridine and its derivatives were superior to all other bases in terms of reaction speed and intensity of the generated light and outshone imidazole, which hitherto has been considered as the best catalyst. The light intensity was related to the difference in pK a between the 4-aminopyridine catalyst and the leaving group of the reagent, and the optimum ∆pK a was found to be close to 0. Similarly, high light intensities were obtained when mixtures of the imidazole analogue 1,2,4triazole and the strong, nonnucleophilic base 1,2,2,6,6pentamethylpiperidine acted as catalysts. The mechanism behind this was concluded to be a "base-induced nucleophilic catalysis", where the ancillary strong base assisted the production of the highly nucleophilic 1,2,4-triazolate anion, which as the actual catalyst then participated in the formation of a more reactive transient reagent. All the investigated catalysts reduced the light yield of the reaction due to base-catalyzed breakdown reactions of the reagents and/or intermediates. The intensity peak maximums of these bright and fast reactions typically appeared after less than 10 ms, whereafter the light decayed to darkness within a few seconds. These reaction characteristics are especially advantageous for sensitive detection applications where the observation volumes and times are limited, e.g., peaks emerging from a capillarybased separation process.

Research paper thumbnail of Determination of C-21 Ketosteroids in Serum Using Trifluoromethanesulfonic Acid Catalyzed Precolumn Dansylation and 1,1‘-Oxalyldiimidazole Postcolumn Peroxyoxalate Chemiluminescence Detection

Analytical Chemistry, 1998

A new procedure for the quantitation of C-21 ketosteroids using trifluoromethanesulfonic acid-cat... more A new procedure for the quantitation of C-21 ketosteroids using trifluoromethanesulfonic acid-catalyzed precolumn dansylation and coupled column liquid chromatographic separation, followed by postcolumn 1,1′-oxalyldiimidazole peroxyoxalate chemiluminescence detection is presented.

Research paper thumbnail of Heterocyclic compounds as catalysts in the peroxyoxalate chemiluminescence reaction of bis(2,4,6-trichlorophenyl)oxalate

Analytica Chimica Acta, 1998

Substituted imidazoles and leaving groups known from other areas of chemistry have been tested fo... more Substituted imidazoles and leaving groups known from other areas of chemistry have been tested for catalytic ef®ciency in the peroxyoxalate chemiluminescence (PO-CL) reaction, using bis(2,4,6-trichlorophenyl)oxalate (TCPO) as reagent. Catalytic activity was found for 1,2,4-triazole, 1-methylimidazole, 2-methylimidazole, 4-methylimidazole and 4,5-dichloroimidazole, while 2-mercaptoimidazole, 2-nitroimidazole, 4-nitroimidazole, benzimidazole, benzotriazole, thiazole, o-benzoic sul®mide, phthalimide, succinimide, 2(1H)-pyridone and 1,2,3-benzotriazine-4(3H)-one yielded no detectable chemiluminescence under the conditions used. None of the tested compounds was more ef®cient than imidazole in catalyzing the PO-CL reaction. Spectrophotometric measurements of the catalytic breakdown of TCPO showed that an intermediate was formed with almost all catalysts, and that intermediates that were more stable or present at lower concentration led to a reduced catalytic ef®ciency in the PO-CL reaction of TCPO. # 1998 Elsevier Science B.V. 0003-2670/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. P I I S 0 0 0 3 -2 6 7 0 ( 9 8 ) 0 0 0 2 9 -4

Research paper thumbnail of Very fast peroxyoxalate chemiluminescence

Peroxyoxalate chemiluminescence (PO-CL) detection offers an advantage in chromatographic detectio... more 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.

Research paper thumbnail of Noise characteristics and analytical precision of a direct injection high efficiency and micro concentric nebuliser for sample introduction in inductively coupled plasma mass spectrometry

Journal of Analytical Atomic Spectrometry, 2002

ABSTRACT Noise power spectra and analytical precision data were generated and compared for a dire... more ABSTRACT 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.

Research paper thumbnail of The origin of peristaltic pump interference noise harmonics in inductively coupled plasma mass spectrometry

Journal of Analytical Atomic Spectrometry, 2002

... Acta, Part B, 1989, 44, 649 CrossRef Search PubMed . 6, E. Björn, T. Jonsson and D. Goitom, J... more ... Acta, Part B, 1989, 44, 649 CrossRef Search PubMed . 6, E. Björn, T. Jonsson and D. Goitom, J. Anal. At. ... Acta, Part B, 1982, 37, 1075 CrossRef Search PubMed . 10, SO Engblom, JC Myland and KB Oldham, J. Electroanal. Chem., 2000, 480, 120 CrossRef CAS Search PubMed . ...