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University of Helsinki Faculty of Science
 
Analytical Chemistry

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Marja-Liisa Riekkola
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AEROSOL NANOPARTICLES

Sophisticated Instrumental Techniques in the Elucidation of Organic Compounds in the Formation Process of Aerosol Particles

Motivation

Atmospheric aerosol formation consists of a complicated set of proc­esses that include the production on nanometer-size clusters from gaseous vapours, the growth of these clusters to detectable sizes, and their simultaneous removal by coagulation with the pre-exist­ing aerosol particle population. Once formed, aerosol particles need to grow further to sizes >50-100 nm in diameter before they are able to influence climate, even though smaller particle may influence human health and atmospheric chemistry. Although aerosol formation followed by growth has been observed to take place almost everywhere in the atmosphere as shown by prof. Markku Kulmala’s research group, serious gaps in our knowledge regarding this phenomenon exist. Although considerable efforts have been de­voted to the analysis of the chemical compounds responsible for the formation and growth of freshly produced aerosol particles, the specific pathways have not been experimentally veri­fied. The Laboratory of Analytical Chemistry is responsible for elucidating the chemical composition of aerosols in the research project belonging to the ‘Centre of Excellence in Atmospheric Science – From Molecular and Biological processes to The Global Climate (2014-2019). on the interaction between the biosphere, aerosols, clouds and climate. Academy prof. Markku Kulmala from the Department of Physical Sciences at the University of Helsinki bears the main responsibility for the centre (http://www.atm.helsinki.fi/FCoE/).

Atmospheric aerosol particles comprise a complex mixture of inorganic and organic compounds. The number of aerosol particles can rise as high as hundreds of thousands/cm3, and the corresponding mass can be hundreds of mg/m3, while the size of the particles ranges from a few nm to a few hundred µm. Depending on the site and the amount of pollution, organic compounds may represent up to 70% of the total dry fine particle mass in the lower troposphere, and the number of organic com­pounds in aerosol particles may be several hundred. The study of the organic composition of freshly-nucleated particles is currently impossible with commercially-available instrumentation. Novel instrumental techniques including sampling and analysis of organic compounds are required, in addition to in situ measurements in order to obtain highly time-resolved analyses that are capable of showing changes in aerosol chemistry.

Short sampling periods are necessary for a reliable knowledge of concentration trends with time during particle formation events. Moreover, size-separating sampling techniques are especially beneficial for a clear picture of the compounds participating in the particle formation. The particle-into-liquid sampler (PILS) combines two conventional techniques in aerosol measurement: particle growth in oversaturated water vapor and further impaction on quartz impactor. Even though several interesting and important studies have been performed with PILS, it has not been applied to the analysis of individual organic compounds. The applicability of PILS to the collection of organic compounds in aerosol samples is actively studied in our research project.

Due to the low concentrations of organic compounds in rural atmospheres, and the errors occurring during sampling, portable aerosol mass spectrometry, suitable for in situ measurements, have been constructed in the Laboratory. It includes integrated size separation of particles, sampling, ionization and analyzing steps for the elucidation of the organic nature of the ultrafine particles (< 50 nm) in the aerosol formation process, and for the production of the signature of the size separated aerosol particles and the organic material. In addition, due to the great complexity of the carbonaceous fractions the analysis of aerosol samples by a single chromatographic technique often fails or is unsatisfactory because of poor separation effi­ciency. Efficiency can, however, be improved with the use of multidimen­sional techniques, employed in the Laboratory of Analytical Chemistry, i.e. by combining two or more techniques in such a way that the best features of each can be utilized. In addition, carefully selected organic compounds can be used as markers that reflect different states and stages of aerosol formation. The use of markers reveals the quantitative and qualitative pattern of those organic compounds that play important roles in the different stages of aerosol formation processes. Furthermore, non-linear data analysis and self organizing maps are employed in the data analysis for the clarification of correlations between the different parameters that affect aerosol formation.

The aerosol research project is headed by prof. Marja-Liisa Riekkola in the Laboratory, and Docent Kari Hartonen, who is responsible for aerosol mass spectrometry, is acting as the second supervisor.

Sampling valve

Figure . A special sampling valve for collection and desorption of aerosol particles into the mass spectrometer.

Objectives

To develop new sampling techniques for aerosol particle analysis
To develop and construct sophisticated instrumental techniques applicable to in situ analysis of organic composition of the preselected aerosol particles.
To apply both aerosolomic fingerprinting and aerosolomics profiling for revealing the pattern of organic compounds in the different stages of aerosol formation processes.

Projects


Hyphenated instrumental techniques in the elucidation of oxidized organic compounds in the preselected size aerosol particles.
  Potential of self constructed aerosol time-of-flight mass spectrometer including sampling, ionization and analyzing steps in the elucidation of the organic nature of the growing particles, and in the production of the signature of the preselected size aerosol particles and the oxidized organic material.

 

NEOTERIC BIOMIMICKING TECHNIQUES FOR HUMAN NANODOMAIN STUDIES

Ingenious electrochromatographic approaches for in-capillary, human lipoprotein, proteoglycan and collagen interaction studies

Motivation

Capillary electromigration techniques, well-recognised for efficient separations, can be exploited also as biomimicking instrumental techniques applicable to studies on the understanding of the molecular properties of human surface nanodomains. In our previous studies, we have shown that human microemulsions and several lipoproteins can be immobilized onto the inner wall of fused silica capillaries in electrochromatography applicable to different interaction studies. The coating procedures have recently been developed and also optimized for aortic proteoglycans, and for collagen I and III. The interactions of collagen I and collagen III with other extracellular matrix components, such as decorin and chondroitin-6-sulfate, have been clarified. In addition, the interactions between positive, neutral and negative peptide fragments of apolipoprotein B-100 (apoB-100), the main protein of low-density lipoprotein particles, and proteoglycans, collagen and collagen-decorin coatings have been elucidated. Low-density lipoprotein coated capillaries have also been used for the in situ isolation of apoB-100 from LDL particles through treatment with the non-ionic surfactant Nonidet P-40. The in situ delipidation of LDL particles in capillaries represents a novel approach for the isolation of immobilized apoB-100, and for the determination of its pI value. Atomic force microscope images have produced valuable topography on different human biomaterial coatings on the capillary wall. At the moment the studies are continued for the elucidation of lipoprotein-collagen and lipoprotein-collagen interactions. In addition, new studies are on-going for the development of sophisticated integrated microdevice for fast lipoprotein analysis including lipoproteins selective isolation from plasma, dynamic dye labelling and separation, all steps carried out in the same microchip. Different nanoscale functional studies are carried out in close co-operation with the Wihuri Reseach Institute (Prof. Petri Kovanen and docent Katariina Öörni) and the National Public Health Institute(Doc. Matti Jauhiainen).

Even though the large body of information on glycosaminoglycans exists, the knowledge is not thorough enough to allow full understanding on their functions. Nowadays modeling allows the construction of a comprehensive atomistic models needed, and modeling of the interactions including glycosaminoglycans will be of fundamental importance for gaining insight into our understanding of complex biological processes. The molecular dynamics simulations are actively utilized for providing measures about the interactions between the peptide residues of apolipoproteins and different glycosaminoglycans. The computational studies are carried out in co-operation with the Department of Physical Sciences, University of Oulu (dos. Marja Hyvönen).

Coating with lipoprotein

Figure. Fused silica capillary coated with lipoprotein particles, and an atomic force microscope image of lipoprotein coating.

Objectives

To develop miniaturized neoteric instrumental techniques applicable to in situ studies focusing on atherogenic nanoscale functions including lipoprotein interactions with proteoglycans and collagen I and III.
To utilize molecular dynamics simulations for the clarification the interactions of apolipoprotein B and apolipoprotein E peptide residues with different glycosaminoglycans.

 

FIELD-FLOW FRACTIONATION

Continuous Two-Dimensional Field-Flow Fractionation

Motivation

Two-dimensional field-flow fractionation (2D-FFF) is a new class of instrumental techniques devised for continuous fractionation of soluble macromolecules and particles. The sample mixture is introduced into a disc-shaped channel and the separated sample components are collected continuously from the channel outlets. The method is based on a two-dimensional fractionation mechanism with radial and tangential flow components in the channel. The technique can be applied to preparative continuous separation of macromolecules, particles and cells. Laboratory engineer Matti Jussila is also actively involved in the project.

Figure. Continuous two-dimensional thermal ThFFF instrument

Objective

To formulate basic theoretical equations needed for optimum performance of the continuous separation systems, and for analytical and preparative applications.

Project

  Continuous Two-Dimensional Thermal Field-Flow Fractionation of Polymers