No description available.

Analytical chemical information is needed in all areas of human activity including health care, pharmacology, food control and environmental chemistry. Today one of the main challenges in analytical chemistry is the development of methods to perform accurate and sensitive rapid analysis and monitoring of analytes in ‘real’ samples. Electrochemical biosensors are ideally suited for these applications. Despite the wide application of electrochemical biosensors, they have some limitations. Thus, there is a demand on improvement of biosensor performance together with a necessity of simplification required for their mass production. In this thesis the work is focused on the development of electrochemical sensors with improved performance applicable for mass production, e.g. by screen printing. Biosensors using immobilized oxidases as the bio-recognition element are among the most widely used electrochemical devices. Electrical communication between redox enzymes and electrodes can be established by using natural or synthetic electron carriers as mediators. However, sensors based on soluble electronshuttling redox couples have low operational stability due to the leakage of water-soluble mediators to the solution. We have found a new hydrophobic mediator for oxidases – unsubstituted phenothiazine. Phenothiazine and glucose oxidase, lactate oxidase or cholesterol oxidase were successfully co-immobilized in a sol-gel membrane on a screen-printed electrode to construct glucose, lactate and cholesterol biosensors, respectively. All elaborated biosensors with phenothiazine as a mediator exhibited long-term operational stability. A kinetic study of the mediator has shown that phenothiazine is able to function as an efficient mediator in oxidase-based biosensors. To improve sensitivity of the biosensors and simplify their production we have developed a simple approach for production of graphite microelectrode arrays. Arrays of microband electrodes were produced by screen printing followed by scissor cutting, which enabled the realization of microband arrays at the cut edge. The analytical performance of the system is illustrated by the detection of ascorbic acid through direct oxidation and by detection of glucose using a phenothiazine mediated glucose biosensor. Both systems showed enhanced sensitivity due to improved mass transport. Moreover, the developed approach can be adapted to automated electrode recovery. Finally, two enzyme-based electrocatalytic systems with oxidation and reduction responses, respectively, have been combined into a fuel cell generating a current as an analytical output (a so-called self-powered biosensor). This was possible as a result of the development of the phenothiazine mediated enzyme electrodes, which enabled the  construction of a cholesterol biosensor with self-powered configuration. The biosensor generates a current when analyte (cholesterol) is added to the cell. The biosensor has been applied for whole plasma analysis. All developed concepts in the thesis are compatible with a wide range of applications and some of them may even be possible to realize in a fully integrated biosensor unit based on printed electronics.

Chemicals entering the market have been steadily increasing. The Swedish Chemicals Agency is in control of the Swedish Products Register, which is storing information on chemicals  manufactured in, transferred, or imported into Sweden. Applied to the register comes the exposure index predicting exposure of chemicals. For this study, the exposure index was used to make a first prioritization of chemicals with potential of exposure to consumers, the list of suspects were further prioritized by in silico predicted physiochemical properties. Six synthetic antioxidants 2,4-di-tert-butylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,4,6-tris-tert-butyl-phenol, 2,2´-methylene-bis(4-methyl-6-tert-butylphenol), 4,4´-methylene-bis(2,6-di-tert-butylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenol) propionate), were selected for target analysis. Great care to background contamination is applied since the analytes are used in everyday objects such as food package and personal care products. Human serum samples was collected from “Blodcentralen” in Stockholm, Sweden. Previous analytical methods exist for individual and combination for a few analytes but lacks in combination of all selected analytes. A previous method for the extraction without clean-up of some of the analytes in serum were tested but lacked in efficiency for all analytes, hence an clean-up step for removal of lipids were added. A gas chromatography mass spectrometry method was developed for simultaneous analysis of the six analytes. Four of the target analytes were detected and three were quantified (2,4-di-tert-butylphenol 2.20-3.33 ng/mL, 2,6-di-tert-butyl-4-methylphenol 3.22-3.93 ng/mL and 2,4,6-tris-tert-butyl-phenol 0.054-0.104 ng/mL). 2,2´-methylene-bis(4-methyl-6-tert-butylphenol) was detected in high concentration but due to linearity problems (R2<0.99) it was not quantified. To the best of my knowledge this is the first time that 2,4,6-tri-tert-butylphenol and 2,2´- methylene-bis(4-methyl-6-tert-butylphenol) have been detected in human serum.

No description available.

This thesis presents two new concepts for separation of micro particles using dielectrophoresis, demonstrated by calculated examples, as well as a new method for obtaining dielectric data on living cells. The thesis is based on four papers. Paper I describes how the trapping efficiency of micro particles may be significantly increased when superpositioned electric fields are employed in a high conductivity medium. Avoiding low conductivity media is important when working with living cells. Calculations were performed to predict trajectories of Escherichia coli bacteria in the system with superpositioned electric fields, and a model was developed which employed two arrays of interdigitated electrodes in a micro channel. Paper II proposes a new concept for separation of micro particles, based on repetitive dielectrophoretic trapping and release in a flow system. Calculations show that the resolution increases as a direct function of the number of trap and release steps, and that a difference in size will have a larger influence on the separation than a difference in dielectrophoretic properties. Polystyrene beads in deionized water were used as a model, and calculations were performed to predict the particle behavior and the separation efficiency. It should be possible to separate particles with a size difference of 0.2 % by performing 200 trap-and-release steps. The enhanced separation power of multi step dielectrophoresis could have significant applications, not only for fractionation of particles with small differences in size, but also for measuring changes in surface conductivity. Paper III presents a new calculation method for predicting dielectrophoretic motion of micro particles. The method is based on a soft sphere method often used in molecular dynamics. Results from the calculations are in good agreement with theoretical predictions as well as initial experimental results, showing that the method provides good efficiency and accuracy. Paper IV describes a new method for measurements of conductivity of living bacteria. To obtain reliable conductivity values, it is important to handle the cells as gently as possible during the measurement process. A standard conductivity meter was used in combination with cross-flow filtration. In this way, repeated centrifugation and resuspension is avoided which otherwise may cause damage to the bacteria. The conductivity of Bacillus subtilis was determined to be 7000 μS/cm by means of the cross-flow filtration method, and the values differ from earlier published values by almost an order of a magnitude. In addition to the work presented in the papers, some experimental dielectrophoresis work in chip-based systems was performed. The behavior of Escherichia coli and polystyrene beads at different voltages and frequencies were studied. Separation of beads with different sizes was achieved on an array of interdigitated electrodes. Using electrodes with a pointed shape, alignment in different directions, pearl-chain formation, rotation, and other dielectrophoretic motion of E. coli were observed. / QC 20101108

Research concerning lignin has increased during the last years due to its renewability and ready availability in black liquor at pulp mills. Today, the kraft lignin found in black liquor is used as a fuel to gain energy in the recovery boiler at the mill. However, a new isolation concept, LignoBoost®, has enabled isolation of part of the lignin while allowing the use of black liquor as a fuel. This isolated lignin can be utilised as a fuel in, for example, thermal power stations or further upgraded to more value-added products. In this context, the most interesting value-added product is carbon fibre. The demand for carbon fibre has increased, but the biggest obstacle for a more extended use is the high production cost. About half of the production cost is related to the raw material. In this work, the possibility of using kraft lignin as a precursor for carbon fibre production has been investigated through fundamental studies. Kraft lignins originating from birch, Eucalyptus globulus, softwoods and softwoods from liner production have been studied. By separating the lignin while still in solution in the black liquor, unwanted large particles such as carbohydrates can easily be removed. After isolation according to the LignoBoost process and purification with the use of an ion-exchanger, the lignins have been both chemically and thermally characterised. Identification of the released compounds at different temperatures has been performed because only 40% of carbon relative to original lignin remains, down from theoretical 60% after thermal treatment up to 1000°C. The main released compounds were phenols, as revealed by pyrolysis-GC/MS. Additionally, a pre-oxidation was done in order to try to stabilise the lignins. It was shown that an oxidation prior to the thermal treatment increases the yield by more than 10% and that the main release of compounds takes place between 400°C and 600°C. Fractionated lignin is better qualified as raw material for carbon fibre production because it is purer and its softening temperature can be detected. Fractionated kraft lignins from all investigated wood sources have high possibilities to act as precursors for the manufacture of carbon fibre.

Nuclear Magnetic Resonance (NMR) is a technique with several advantages, such as high rapidity and easy operation as no sample specific standard or sample derivatization is required. Proton NMR is the most common NMR experiment, since hydrogen is “NMR active” and present in most organic compounds. Because of this, there is a high risk of overlapping signals in 1H-NMR spectra in samples containing multiple components, e.g. pharmaceutical preparations. Since Fluorine (19F) is “NMR active”, but not as common in organic molecules as hydrogen, peak overlapping is unlikely. A quantitative 19F-NMR method was therefore developed in this study.   Certain parameters (number of scans, relaxation delay, excitation frequency, pre-scan delay, spectral width & pulse angle) were examined during the method development, based on samples containing fludrocortisone acetate and 4,4´-difluorobenzophenone. For evaluation of the developed method, experiments were set up with different active pharmaceutical ingredients as well as pharmaceutical products. Good linearity and precision was obtained, and conclusions from the research experiments are that the developed method gives reliable purities compared to the reference method 1H-qNMR, and can therefore be used to achieve estimated assays on pharmaceutical raw materials. The method is also applicable on analysing registered pharmaceutical products as well as determining whether the strength of a suspected illegal drug is within the therapeutic range or not. Finally, the range of the method was determined to approximately 1-20 mg/mL, if examined on a 300 MHz NMR instrument.

Dissolved organic matter (DOM) is the prevalent form of organic carbon in most aquatic environments. It is an ultra-complex mixture that plays a crucial role in global carbon cycling. Despite its importance it is still poorly understood due to its extreme heterogeneity and intricacy. Major advances in chemical characterization of DOM were possible with the introduction of high-resolution mass spectrometry (HRMS). This technique, in combination with direct infusion (DI) as sample introduction, is the most powerful tool for the DOM analysis to date. A compelling alternative to DI is represented by upfront separation with liquid chromatography (LC); however, current techniques involve only offline LC-HRMS approaches, which exhibit important logistical drawbacks, making DOM analysis more challenging. The aim of the presented studies was to develop new methods able to enhance the analysis of the dissolved organic matter and enable a wider range of researchers to participate in the advancement of this field. In the first study, the application of the Orbitrap mass spectrometer for resolving complex DOM mixtures was investigated and the results were compared to the more established state-of-the-art technique, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The Orbitrap was capable of excellent reproducibility and detection of the majority of ionizable organic molecules in typical aquatic mixtures. The main disadvantage of the technique is that fewer molecular formulas can be resolved and detected because of lower resolution and sensitivity. This means that many sulfur peaks and all phosphorous containing peaks are not determined. Despite this drawback, our results suggest that the Orbitrap is an appropriate technique for the investigation of very subtle biogeochemical processing of bulk DOM. The lower costs (purchase and maintenance) and wider availability of Orbitrap mass spectrometers allow a greater number of laboratories to participate in the characterization of DOM. In the second study, the first online method involving reverse phase chromatography and ultrahigh resolution mass spectrometry for the analysis of DOM was developed. This method overcomes the disadvantages of typical offline approaches. It enhances enormously the amount of information achievable in a single run, maintaining high resolution data, reducing analysis time and potential contamination. The introduction of in silico fractionation makes the method extremely flexible, allowing an easy, fast, and detailed comparison of DOM samples from a variety of sources.

Ion pair chromatography has found many uses within analytical chemistry and understanding of the chromatographic process with an ion-pairing reagent have been studied since the 1970s. The adsorption of the Ion-pairing reagent to the stationary phase is understood to be important and many studies have been dedicated to looking at the adsorption isotherms of the earlier quaternary alkylammonium ions. Trialkylamines have been found to have some advantages over quaternary alkylammonium ions and are almost exclusively used in the analysis of oligonucleotides. Despite this there is a lack of studies looking at the adsorption isotherms of these molecules. A method for determining the adsorption isotherm of triethylamine and tributylamine was recently published by Haseeb et al. (2023) were the adsorption isotherm of tributylamine displayed and unusual behaviour. This raised the question of how the adsorption isotherm of the ion-pairing reagent relates to the retention of the analytes, which is the topic of this project. The retention factor of a set of carboxylic and sulfonic acids were determined at increasing concentration of triethylamine and tributylamine. The retention data was used to assess the validity of the electrostatic retention model by Ståhlberg and the Extended thermodynamic approach by Cecchi, as both these models can be used to relate the adsorption to the retention factor. Results from triethylamine were harder to interpret and tributylamine subsequently became the main focus of the project. The results from tributylamine showed a clear division between carboxylic and sulfonic acids in terms of selectivity and determined surface potential. This could not be explained by the electrostatic retention model and led to the adoption of the Cecchi retention model. The adsorption isotherm of tributylamine was determined by two methods and used to fit the Cecchi model to the retention data of three analytes. This could potentially be used to interpret the adsorption isotherms influence on the retention factor, although the attained relationship should be questioned due to uncertainty in the determined adsorption isotherms.

There currently exists no commercialized method for rapid sampling and analysis of trace tar ingas streams. Solid phase microextraction (SPME) with a polydimethylsiloxane (PDMS) solidphase has been previously investigated as a possible candidate due to its solvent-free natureand reusability. This project set out to deliver a proof of concept study to test whether SPMEcan be sufficiently tuned to analyse trace tar content in syngas below the concentration of 0.1mg/Nm 3 . Due to complications that arose from the Covid-19 pandemic, it was unfeasible tocarry out the practical elements of the project. Instead a concept design for carrying out such astudy has been successfully developed. This design envisions a two-chamber setup able tosample syngas directly from a gasifier at 60 °C and 125 °C respectively and is illustrated in thetext. It utilizes commercially available solvent tubes to cross-check and verify the SPME results. / I nuläget finns det ingen kommersiell metod för att snabbt extrahera och analysera spår av tjärkomponenteri gasströmmar. Tidigare har solid phase microextraction (SPME) medpolydimetylsiloxan (PDMS) som fast fas undersökts som en möjlig kandidat då den ej kräverlösningsmedel och kan enkelt återanvändas. Detta projekt hade som mål att bevisa att SPMEkan anpassas tillräckligt känsligt för att analysera spår av tjära i syngas med en koncentration påmindre än 0,1 mg/Nm 3 . På grund av komplikationer som uppstod i samband med Covid-19pandemin var det inte möjligt att utföra den praktiska delen av projektet. Istället så har endesign tagits fram för ett koncept som beskriver hur man kan genomföra den praktiska delen.Designen beskriver en två-kammare lösning som kan användas för att ta prover från syngas somkommer direkt från en förgasare. Proverna tas vid temperaturer om 60 °C och 125 °C för attuppnå maximal känslighet. En uppsättning kommersiellt tillgängliga sorbentrör används för attkontrollera resultaten från SPME.