Biomedical subjects

M L Riekkola

Publications and source records attributed to M L Riekkola.

At least 19 recordsLinked to original sources

PubMed2004

Determination of pesticides in red wines with on-line coupled microporous membrane liquid-liquid extraction-gas chromatography.

Microporous membrane liquid-liquid extraction (MMLLE) was coupled on-line with gas chromatography for the determination of pesticides in wine. The MMLLE-GC provided to be efficient and selective and the method was linear, repeatable and sensitive. The limits of detection ranged from 0.05 to 2.3 microg/l and the limits of quantification were 0.2-7.5 microg/l for all the analytes using FID as detector. With MS detection LODs in the range 0.03-0.4 and LOQs of 0.3-3.5 microg/l were achieved. The method was applied to the determination of pesticides in several red wines of different origin.

Chromatography, Gas↗

PubMed2001

Use of a partial filling technique and reverse migrating micelles in the study of N-methylcarbamate pesticides by micellar electrokinetic chromatography-electrospray ionization mass spectrometry.

This study describes three ways to couple micellar electrokinetic chromatography (MEKC) on-line with electrospray ionization mass spectrometry (ESI-MS) for the analysis of N-methylcarbamate pesticides. The methods involved the use of a partial filling (PF) technique under basic conditions and the use of reverse migrating micelles (RMMs) under acidic and basic conditions. The use of RMMs in basic electrolyte solutions required coated capillaries with low electroosmotic flows, and capillaries coated with anionic poly(sodium 2-acrylamide-2-methylpropanesulfonate) were selected for the purpose. Before the on-line MEKC-ESI-MS coupling, the MEKC and MS conditions were separately optimized under off-line conditions. The methods were compared in terms of detection limits and the stability of the electrospray process. The PF method offered good separation but poorer stability of the electrospray relative to the other methods. A more stable electrospray performance was obtained with use of RMMs in acidic electrolyte solutions, but some of the analytes were protonated and could not be detected due to the increase in their retention factors. However, with the use of anionic polymer-coated capillaries and RMMs at pH 8.5, all analytes were successfully separated. The high-salt stacking method was applied to improve the sensitivity of MEKC-ESI-MS and the detection limits were in the range of 0.04-2.0 microg/ml.

Carbamates↗

PubMed2001

Oxidation of 4-chloro-3-methylphenol in pressurized hot water/supercritical water with potassium persulfate as oxidant.

4-Chloro-3-methylphenol (c = 2.0 mM), representing a model pollutant, was oxidized in pressurized hot water and in supercritical water in a continuous flow system. Potassium persulfate was used as oxidant in concentrations of 8.0 and 40.0 mM. Contact times (reaction times) were 3-59 s, temperatures 110-390 degrees C, and pressures 235-310 bar. A wide temperature range was tested to determine the range over which potassium persulfate can be used effectively. Good oxidation efficiencies for 4-chloro-3-methylphenol were obtained at both oxidant concentrations and with short contact times at temperatures clearly underthe critical temperature of water; total organic carbon content of the effluent was low under optimized conditions. Corrosion, measured as nickel and chromium concentrations of the effluent, was more severe at oxidant concentration of 40.0 mM. Sulfate was present in the effluent in high concentrations. Sulfate is the limiting factor in the use of potassium persulfate in wastewater treatment and requires further water treatment.

Oxidants↗

PubMed2001

Electrophoretic mobilities of cationic analytes in non-aqueous methanol, acetonitrile and their mixtures. Influence of ionic strength and ion-pair formation.

The mobilities of cationic analytes in organic solvents and water are compared, and the reasons for differences in the mobilities are discussed in detail. Actual mobilities (at background electrolyte concentration 10 mmol/l) of anilinium ions were determined by capillary zone electrophoresis in water, methanol, acetonitrile and mixtures of methanol and acetonitrile (in volume ratios 1:1, 1:3 and 3:1). The actual mobilities correlated with the viscosity of the organic solvent: the products of actual mobility and viscosity were constant within 7%. However, these products were significantly larger in water. Larger products of mobility and viscosity in water were also found for unsubstituted anilinium when the absolute mobility (at zero ionic strength) was taken into consideration. Thus, ion-solvent interactions must be responsible for the seemingly high mobility in water compared with that in organic solvents. This finding can be explained by the effect of the ion on the water structure. Based on equilibrium constant for ion-pair formation given in the literature, about 20% of the main background electrolyte constituent (tetrapropylammonium perchlorate) is associated at 10 mmol/l concentration in acetonitrile. Comparison of the plot of the measured mobilities of the analytes vs. the square root of the corrected ionic strength of the background electrolyte in acetonitrile with the prediction based on the Debye-Hückel-Onsager theory showed the measured mobilities deviate negatively from the theoretical line. This is apparently due to ion pairing, which takes place for the analytes as well.

Acetonitriles↗

PubMed2001

Extremely high electric field strengths in non-aqueous capillary electrophoresis.

The influence of high electric field strength on the separation of basic analytes in non-aqueous alcohol background electrolyte (BGE) solutions was investigated. Increasing the separation voltage in capillary electrophoresis (CE) may be advantageous if the conductivity of the BGE solution is low enough to allow fast separations without excessive Joule heating or band broadening. The voltage range tested was 20-60 kV with methanol and ethanol, and 25-60 kV with propanol and butanol as solvent for BGE. The resulting electric field strengths ranged from 660 V cm(-1) to 2000 V cm(-1). Experiments were made with a special laboratory constructed CE instrument. The separation efficiency vs. voltage curve was found to vary with the alcohol BGE solution. The increase in voltage decreased the separation efficiency in the case of methanol BGE solution, but with the other BGEs a clear efficiency maximum was obtained above 30 kV. The highest separation efficiencies were achieved with propanol BGE solution, where the efficiency maximum was reached at 45 kV. However, reasonable efficiency was achieved even at 60 kV. The extent of Joule heating was determined by calculating the temperature inside the capillary and the observed plate heights were interpreted in terms of the Van Deemter equation. The decrease in the separation efficiency with higher voltage was attributed mainly to Joule heating in the case of methanol and ethanol BGE solution and to the analyte adsorption on the capillary wall with propanol and butanol BGE solutions.

Electricity↗

PubMed2001

Capillary zone electrophoresis of basic analytes in methanol as non-aqueous solvent mobility and ionisation constant.

The electrophoretically relevant properties of monoacidic 21 bases (including common drugs) containing aliphatic or aromatic amino groups were determined in methanol as solvent. These properties are the actual mobilities (that of the fully ionised weak bases), and their pKa values. Actual mobilities were measured in acidic methanolic solutions containing perchloric acid. The ionisation constants of the amines were derived from the dependence of the ionic mobilities on the pH of the background electrolyte solution. The pH scale in methanol was established from acids with known conventional pK*a values in this solvent used as buffers, avoiding thus further adjustment with a pH sensitive electrode that might bias the scale. Actual mobilities in methanol were found larger than in water, and do not correlate well with the solvent's viscosity. The pK*a values of the cation acids, HB-, the corresponding form of the base, B, are higher in methanol, whereas a less pronounced shift was found than for neutral acids of type HA. The mean increase (compared to pure aqueous solution) for aliphatic ammonium type analytes is 1.8, for substituted anilinium 1.1, and for aromatic ammonium from pyridinium type 0.5 units. The interpretation of this shift was undertaken with the concept of the medium effect on the particles involved in the acid-base equilibrium: the proton, the molecular base, B, and the cation HB+.

Electrophoresis, Capillary↗

PubMed2001

Study on liposomes by capillary electrophoresis.

Liposomes made of mixtures of zwitterionic and anionic lipids were investigated by means of capillary electrophoresis and dynamic light scattering. The influence of the molar lipid ratio and of the buffers, used in the running electrolyte solution, on the physical characteristics of the liposomes were investigated. Data on effective electrophoretic mobilities, total charges as well as sizes of the liposomes are given. In addition, examples on the use of liposomes as carriers in electrokinetic capillary electrophoresis for the separation of benzene derivatives, steroids, and phenols are shown.

Electrophoresis, Capillary↗

PubMed2001

Determination of iridoid glycosides by micellar electrokinetic capillary chromatography-mass spectrometry with use of the partial filling technique.

A fast and easy method was sought for determination of the iridoid glycosides catalpol, ketologanin, verbenalin, loganin, 8-epi-loganic acid, geniposidic acid and 10-cinnamoyl catalpol in plant samples. The method involved micellar electrokinetic capillary chromatography (MEKC) coupled on-line to mass spectrometry. The partial filling technique and electrospray ionization were used. Seven iridoid glycosides could be separated with use of MEKC under basic conditions. However, 8-epi-loganic acid and geniposidic acid could not be detected simultaneously with the five neutral iridoid glycosides by mass spectrometry. Therefore, only the neutral iridoid glycosides were screened from plant samples. Catalpol, verbenalin, loganin and possibly 10-cinnamoyl catalpol were found in an examination of seven plant species in the genera Plantago, Veronica, Melampyrum, Succisa, and Valeriana. Aucubin, which was not included in the sample mixture used in method development because of overlapping with catalpol in MEKC, was also detected. The limits of detection for the iridoid glycosides, both at the UV and at the mass spectrometer, are given.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2001

Resolution in capillary electrophoresis with nonaqueous methanol as solvent: theoretical prediction and experimental confirmation.

The resolution of the analytes was predicted from their known pKa* values and actual mobilities in nonaqueous methanolic solutions according to theory taking longitudinal diffusion as the only cause for peak dispersion. This leads to an equation of the resolution as a function of the pH*, as both selectivity and efficiency are dependent on the pH of the buffer. The experimentally obtained resolution values were in acceptable agreement with the predicted theoretical ones in most cases. This was demonstrated for substituted benzoic acids as analytes. The pKa* values needed for the calculation of the resolution were derived from the pH* dependence of the effective mobility. The pH* scale in methanol was based on conventional pKa* values of acetic acid and chloroacetic acid taken from the literature.

Benzoates↗

PubMed2001

Novel dynamic polymer coating for capillary electrophoresis in nonaqueous methanolic background electrolytes.

Coated capillaries can be advantageous in many capillary electrophoretic applications where nonaqueous background electrolytes are used. In the present work, a new dynamic polymer coating (poly(glycidylmethacrylate-co-N-vinylpyrrolidone)) for methanol-based background electrolytes is introduced. The magnitude and stability of electroosmotic flow was investigated with coated capillaries at pH* values of 3, 7.8, and 10.4 in methanol. At pH* 7.8 and 10.4 the electroosmotic flow was negligible and repeatable. On the other hand, at pH* 3 a weak, unstable electroosmotic flow was observed, due to a change in the conformation of the polymer under acidic conditions. The dynamically coated capillaries were successfully applied to the separations of cationic drugs, phenols, and benzoic acids. The synthesis and characterization of the polymer are described in detail.

Alprenolol↗

PubMed2001

Determination of biogenic amines in wine by multidimensional liquid chromatography with online derivatisation.

An online multidimensional liquid chromatographic system was developed for online clean-up, derivatisation and separation of biogenic amines in wines. The system consists of a cation-exchange precolumn, a derivatisation coil and an analytical column, and a column-switching valve. The entire system can be easily automated. The method proved to be quantitative and sensitive. Limits of detection were below 0.05 mg l(-1) for all amines and linearity was preserved over the tested range (0.05-15 mg l(-1)). The method was applied to the analysis of red wines of different origin.

Biogenic Amines↗

PubMed2000

Analysis of phenols in pyrolysis oils by gel permeation chromatography and multidimensional liquid chromatography.

A simple method with minimal manual sample preparation was developed for the analysis of phenols in pyrolysis oils. Sample pre-treatment was done by gel permeation chromatography (GPC), where the high-molecular-mass lignins were separated from the phenols. Multidimensional liquid chromatography (LC-LC) was used in the analysis of the phenolic fraction. The pre-column was used for sample clean-up and pre-fractionation before introduction of the phenolic fraction to the analytical column. The repeatability and linearity of the total GPC and LC-LC methods were excellent. The results were in accordance with the reference method in which the sample pre-treatment was done by precipitating the lignins with water, and the phenols were extracted with toluene and analysed by GC-MS.

Chromatography, Gel↗

PubMed2000

Non-aqueous capillary electrophoresis.

The benefits of non-aqueous capillary electrophoresis have been described in a number of recent publications. The wide selection of organic solvents, with their very different physicochemical properties, broadens our scope to manipulate separation selectivity. The lower currents present in non-aqueous solvents allow the use of high electric field strengths and wide bore capillaries, the latter in turn allowing larger sample load. In many cases detection sensitivity can also be enhanced. The potential of non-aqueous capillary electrophoresis is discussed throughout the paper, and the feasibility of capillary electrophoresis under non-aqueous media is demonstrated with reference to several applications.

Electrophoresis, Capillary↗

PubMed2000

Pressurized hot water extraction coupled on-line with LC-GC: determination of polyaromatic hydrocarbons in sediment.

Pressurized hot water extraction (PHWE) was directly combined with a LC-GC system for the determination of polyaromatic hydrocarbons (PAHs) in sediment. The sediment sample was first extracted with pressurized hot water, and the analytes were adsorbed into a solid-phase trap. The trap also functioned as a LC column, which removed most of the interfering matrix components. The 780-microL LC fraction containing the analytes was directly transferred to the GC using an on-column interface. The whole PHWE-LC-GC analysis took place in a closed system, and no sample pretreatment was required. The sensitivity of the method was excellent due to the efficient concentration in the LC-GC system. Sensitivity was approximately 800 times better than in traditional systems. In addition, only a small amount of sample (10 mg) was required for the analysis. The PHWE-LC-GC method proved to be linear in the concentration range of 0.01-2 microg/g, the limits of quantification were below 0.01 microg/g for all the analytes, and the relative standard deviations were between 3 and 28%. LC cleanup and the improved sensitivity made detection with FID sufficient for the determination of analytes. The results were comparable to those obtained in an interlaboratory comparison study as well as to the results obtained with off-line SFE-GC-MS.

Chromatography, Gas↗

PubMed2000

Extraction of iridoid glycosides and their determination by micellar electrokinetic capillary chromatography.

Several methods for the extraction of two iridoid glycosides, catalpol and aucubin, from the plant matrix (Veronica longifolia leaves) were compared. Pressurized hot water extraction and hot water extraction were the most efficient isolation techniques for both. Pressurized liquid extraction and maceration with various organic solvents were also tested. Relative to the amounts extracted with hot water, ethanol extracted only 22% of catalpol and 25% of aucubin and pressurized hot water extracted 83% of catalpol and 92% of aucubin. The lowest relative standard deviations, 22% for catalpol and 8% for aucubin, were achieved with hot water extraction (13 repetitions), and the highest relative standard deviations, 76% for catalpol and 73% for aucubin, with pressurized liquid extraction (five repetitions). A fast capillary electrophoretic method was developed for the quantitative determination of catalpol and aucubin.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2000

Compensation of the siphoning effect in nonaqueous capillary electrophoresis by vial lifting.

Increasing the sample load in nonaqueous capillary electrophoresis through the use of wide-bore capillaries is a good way to scale up analytical separations to semipreparative level. However, obtaining high efficiency requires the use of special instrumentation to eliminate siphoning. When wide-bore capillaries are employed, relatively large solvent volumes are transported from inlet to outlet vial, and due to the difference in liquid levels a siphoning flow from outlet to inlet is established. Siphoning induces a deviation from the plug-like flow profile and adversely affects the separation efficiency. In this study the use of wide-bore capillaries in nonaqueous capillary electrophoresis was examined with compensation for siphoning by lifting of the inlet vial. The inlet vial is raised at a speed appropriate for maintaining equal levels of liquid in the inlet and outlet vials. The optimal lift rate was determined empirically from a series of runs in which the lift rate was varied. As well, a simple theoretical model was devised for the calculation of lift rates. The model was successfully applied for the 200 microm and 320 microm ID capillaries but for the 530 microm ID capillary the predicted optimal lift rate was too low. Evidently this was because the theory was unable to account for the effect of siphoning on the migration times. Three model compounds, bumetanide, furosemide and ethacrynic acid, were separated using an acetonitrile-ethanol mixture (50:50, v/v) with potassium acetate (1 mM) or ammonium acetate (5 mM) as electrolyte. Good separation of bumetadine and ethacrynic acid was obtained even with a 530 microm ID capillary when the lift rate was carefully optimized. Without elimination of siphoning the peaks would not have been detectable. The viscosities and electrical conductivities of the electrolyte solution measured at different temperatures showed that viscosity as well as conductivity decreased with increasing temperature. The temperature dependence of the conductivity was used to estimate the temperature inside the CE capillary.

Electric Conductivity↗

PubMed2000

Liposomes as carriers in electrokinetic capillary chromatography.

Liposomes are small membrane-enclosed vesicles composed of either natural or synthetic lipids. Their size can be adjusted on a wide scale and they can be made with well-defined compositions. While liposomes have been extensively used as model biomembranes they have also gained a considerable degree of attention as carriers for drugs as well as for genetic material. The physical properties of liposomes are critically dependent on their chemical composition. In this study liposomes were applied as pseudostationary phases in electrokinetic capillary chromatography. Various negatively charged liposomes, consisting of mixtures of zwitterionic and anionic lipids, were investigated. Major emphasis was put on clarifying the effects of the total lipid concentration, the lipid molar ratio, the lipid head group, and the buffer on the capillary electrophoretic separation of neutral analytes. In addition, the influence of the physical state of the membrane, ie., gel vs. fluid, on the separation was investigated. Corticosteroids were applied as model analytes.

Adrenal Cortex Hormones↗

PubMed2000

Electrophoretic studies of polygalacturonate oligomers and their interactions with metal ions.

Polygalacturonic acid, a linear homopolysaccharide, was investigated by capillary electrophoresis (CE) using linear polyacrylamide-coated capillaries and laser-induced fluorescence (LIF) detection. A successful separation of its fluorescently labeled oligomers was achieved through sieving in polyacrylamide entangled matrices. The reaction conditions for the derivatization of polygalacturonic acid were optimized. In studying the interactions between polygalacturonic acid and various metal ions, the end-label, free-solution electrophoretic (ELFSE) technique, developed earlier in our laboratory (Sudor, J., Novotny, M. V., Anal. Chem. 1995, 67, 4205-4209) was found preferable to the sieving method. ELFSE is fast and convenient in that no polymer solutions are needed for the separation. The investigation showed that for the moderately large oligomers, the strongest binding occurred with calcium and cadmium ions, while the smallest interaction was observed with magnesium ions.

Cadmium↗