Technological developments have enabled mass spectrometry (MS) to evolve asone of the most versatile, sensitive and widely used analytical methods. Key areas ofresearch in biological MS include the development of analyte-selective MSmethodologies, along with the design of MS compatible separation technology. Analytesof interest range from small, biologically active molecules in disease progressionresearch, to macromolecules such as proteins, in proteomics investigations. Advances inthese areas are vital to maintaining the level of sophistication that has become thebenchmark for MS analyses.Mass spectrometry has found a permanent station in disease progression studies,particularly in biomarker discovery. This is especially true for Alzheimer's disease (AD),a condition marked by widespread lipid peroxidation (LPO) in the brain. The mainhypothesis of the first part of this dissertation is that LPO produces aldehydes that canpotentially be exploited as AD biomarkers. Design of novel LC-MS/MS methods forbrain aldehyde analysis is described. The methods were applied towards aldehydequantification in the hippocampus, superior and middle temporal gyrus and cerebellum ofsubjects with early AD (EAD), mild cognitive impairment (MCI) and age-matchedcontrols. Results obtained indicated elevation of neurotoxic aldehydes in MCI and EADbrain and suggested that LPO occurred early in AD. Understanding AD progression hasbecome important for developing diagnostic methods and treatments.Mass spectrometry is also the major analytical tool in proteomics, where gelelectrophoresis is dominant in pre-MS separations. The main hypothesis of the latter partof this dissertation is that exposure of microbe fermenters including Clostridiumthermocellum to an external stimulus, such as ethanol, can alter the membrane proteome.Design of novel doubled-SDS-PAGE (dSDS-PAGE) methods for membrane proteinanalysis is described, as these proteins are under-represented in standard 2D-PAGE. Thenewly developed Bicine-dSDS-PAGE offered superior separation over other methods andwas applied towards analysis of wild type and ethanol-adapted C. thermocellum cellmembranes. Significant differences in protein expression were observed. Anunderstanding of ethanol adaptation will promote the design of more ethanol-tolerantstrains. Such an outcome can have dramatic effects in the fuel industry as the trendtowards more efficient fuel development gathers momentum.

Real time detection of Volatile Organic Compounds (VOCs) using Selected Ion Flow Tube – Mass Spectrometry (SIFT-MS) provides a unique opportunity for research into breath testing for clinical diagnosis. However, before engaging in research into breath analytes as markers of disease, appropriate breath collection methods are required. Collection of breath for SIFT-MS instruments fall into two categories, direct breath collection into the instrument and the remote breath collection onto a storage medium. This thesis describes the development and validation of both methods of breath collection equipment for SIFT-MS analysis. Development of the direct breath collection device involved standardising and optimising the way in which breath is sampled by SIFT-MS. Design considerations include ergonomics, patient safety, breathing resistance, materials, and appropriate operating conditions of the device. Results from materials testing showed that all materials emit VOCs and the best approach is to minimise VOC emission by careful material selection. To minimise flow resistance experienced by the patient, the capillary from which the SIFT-MS instrument samples, is placed as close as possible to the users mouth. The optimal operating temperature of the device was found to be 100°C - 120°C, which ensures that water vapour will not condense inside the capillary causing blockage. In order to ensure patient safety the device is adequately insulated using stagnant air which also minimises VOC emission from insulation materials. Because a SIFT-MS instrument is large and cannot be easily shifted around a hospital, a system of remote sample collection is required. It is also important to separately collect and analyse breath from the respiratory alveolar region. For this reason the remote breath collection device designed also fractionates collected breath samples into the breath from the upper airways and alveolar breath. The storage medium chosen for the collected breath samples is a gas sampling bag made from Tedlar™. Collection of breath into Tedlar™ bags allows breath to be stored as a whole air sample, the ideal form for analysis with the SIFT-MS technique. Alveolar breath is fractionated from deadspace gasses by measuring a subject's exhalation and collecting the portion of interest. The breath exhalation is measured by an averaging Pitot tube and pressure transducer. Signal processing and automation of the remote breath collection device is controlled by a Cypress Microsystems PSoC microcontroller. To validate the device isoprene and acetone concentrations in fractionated breath samples were compared with a whole breath sample. Results showed that the alveolar breath fraction had a higher concentration of acetone than the upper airway fraction, indicating that the breath was successfully fractioned. However, isoprene concentrations were lower in both fractions due to hyperventilation of the subject causing a dilution effect of alveolar VOCs. Therefore, a higher sample collection volume is required per exhalation, and regulating subjects' breathing rate will avoid the dilution effect observed in collected breath samples. Overall, this thesis had designed, developed and validated two forms of breath collection systems for use with SIFT-MS technology.

No description available.

There is a close relationship between the susceptibility to disease and nutritional state, in the sense that an adequate diet enhances resistance to disease. There is an increasing interest in this beneficial relationship among scientists, food manufacturers and consumers. The trend is moving towards functional foods and their specific health benefits. The results of numerous epidemiological studies and recent clinical trials provide consistent evidence that diets rich in fruits and vegetables can reduce the risk of chronic diseases. These protective effects are mediated through multiple groups of beneficial nutrients contained in the fruits and vegetables, one of these being polyphenol antioxidants. The intake of the polyphenols plays an important role in the reduction and prevention of coronary heart disease (CHD), cardiovascular disease and cancer, as a consequence of their associated antioxidant properties. Fruits contain an array of polyphenols with antioxidant capacity. Polyphenols may be classified in two broad groups namely: flavonoids and non-flavonoids. Flavonoid subgroups in fruits are further grouped as catechins, anthocyanins, procyanidins and flavonol among others. Phenolic acids occur as hydroxylated derivatives of benzoic acid and cinnarnic acid, and are classified as non-flavonoids. Polyphenols have redox properties allowing them to act as reducing agents, hydrogen donators and singlet oxygen quenchers, and thus contribute to the antioxidant capacity of fruits and vegetables. Because of the numerous beneficial effects attributed to these antioxidants, there is renewed interest in finding vegetal species with high phenolic content and relevant biological activities. In view of the importance of these substances towards health and food chemistry, this study will focus on the polyphenol and Vitamin C characterisation and quantification of an indigenous South African fruit, the Kei-apple (Dovyalis cafra), thought to have antioxidant properties. Due to the fact that polyphenol content influences the colour, taste and possible health benefits of the fruit / processed food product, this study will supply valuable information to industry in choosing the best fruit processing methods to attain the desired end product. The exploitation of indigenous South African fruits (Marula and Kei-apple) is receiving increasing prominence, not only due to their health benefits, but also the opportunities these present to rural based economics. Furthermore, this research will serve as a platform for further research on the Kei-apple and other indigenous South African fruits with possible health benefits. Aims: The overall aim of this study is the quantification and characterisation of various nutritionally important antioxidants (polyphenols and ascorbate) in the Kei-apple fruit in its entirety, as well as in its individual fruit components (peel, flesh and seeds). In addition, the total antioxidant capacity of the entire fruit and the various fruit components will be determined in the unfractionated and fractionated fruit extracts. Gas chromatography coupled mass spectrometry (GC-MS) characterisation of the individual polyphenol components will also be analyzed in order to speculate on possible specific health benefits which the Kei-apple may possess. Methods: The study was designed to ensure that a representative fruit sample was collected. Approximately 100 kg Kei-apples were picked in the month of November 2004 from the Bloemhof area in South Africa. A sample of 50 fruits was rinsed and separated into the various components (peel, flesh and seeds). An additional 50 fruits were randomly selected, cleaned and used in their entirety for data representative of the entire fruit. The sample extracts were prepared, after being grounded and lyophilized, by a method described by Eihkonen et al. (1999) using 70% aqueous acetone. The C18-fractionation on the fruit and separated fruit components resulted in four fractions containing (1) phenolic acids; (2) procyanidins, catechins and anthocyanin monomers; (3) flavonols and (4) anthocyanin polymers. The total polyphenol content of the fruit and fruit components as well as the above mentioned C18-fractions were determined by Folin-Ciocalteu's method (Singleton & Rossi, 1965). Both free and total ascorbate concentrations in these samples were determined as described by Beutler (1984), in addition to total sugar content of these via standard methods. Apart from their nutritional interest, both these measurements are necessary for the correction of the total polyphenol concentrations. The total antioxidant capacity of the entire fruit and various fruit components was determined by measuring the oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP) of the unfractionated and fractionated extracts. Using GC-MS analysis, the various individual polyhenol compounds contributing to the total polyphenol content of the Kei-apple was separated, identified and quantified. This quantitative data was captured and statistically analysed. The analysis of variation was performed using the Tukey Honest Significant Difference test for post-hoc comparison. ORAC, FRAP and polyphenol Pearson correlation analyses were performed using Statistics (Statsoft Inc., Tulsa, Oklahoma, USA) with significance set at P ≤ 0.05. Results and discussion: This study determined the presence of various nutritionally important antioxidants (polyphenols and ascorbate), the total antioxidant capacity in the entire fruit as well as in the individual fruit components (peel, flesh and seeds) and their polyphenol sub group fractions. Total phenol content: The Kei-apple, in its entirety, has a polyphenol concentration of 943 ± 20.3 mg GAE/100g dry weight. Comparison of the individual fruit components showed the seeds to have the highest total polyphenol concentration with 1990 ± 31.3 mg GAE/100g dry weight, followed by that of the peel, 1126 ± 45.8 mg GAE/100g dry weight and then that of the flesh, 521 ± 1.01 mg GAE/100g dry weight. Total, L-ascorbic (ASC) and L-dehydroascobic (DHA) concentration: The total ascorbate of Kei-apple fruit is 517 ± 0.92 mg/100g dry weight. In contrast to the polyphenol content, the flesh of the Kei-apple had significantly the highest concentration of total ascorbate 778 ± 1.20 mg/100g dry weight, Gascorbic 241 ± 21.0 mg/100g dry weight, as well as Gdehydroascobic 537 ± 22.2 mg/100g dry weight. The ratio of Lascorbic acidltotal ascorbate for the flesh, entire fruit, peel and seed is 0.31,0.43,0.49,0.95, respectively, indicating the seeds are the most stable source of biologically active Vitamin C, with 95% of the total ascorbate occurring as G ascorbate. This is also in line with the total polyphenol content of these components, confirming a polyphenol sparing effect on ascorbate. C18-fractionation extracts: Solid phase (C18) fractionation of the Kei-apple fruit and fruit components showed that the fruit, peels and seeds consist predominantly of phenolic acids, followed by procyanidin, catechin and anthocyanin monomers and thereafter varying amounts of anthocyanin polymers and flavonols. Antioxidant capacity: The antioxidant capacity of the entire fruit and individual fruit components as determined by ORAC, (r=0.76) and FRAP, (r=0.95) significantly correlated with the total polyphenol content, as well as to each other (r=0.88), indicating both to be good predictors of antioxidant capacity. GC-MS polyphenol characterisation of the Kei-apple: Caffeic acid and hydro-p-coumaric acid were seen to be the phenolic acids occurring in the highest concentrations in the Kei-apple fruit. The majority of these are concentrated in the flesh and in the case of caffeic acid, also in the peel. The order of predominance of other major non-flavonoid components in the whole fruit analysis are m-hydroxybenzoic acid > p-hydroxyphenyl acetic acid > 3-methoxy-4- hydroxyphenylpropionic acid > p-coumaric acid. The peel of the Kei-apple, apart from caffeic acid, has exceptionally high concentrations of ferulic acid and also serves as a source of protocatechuic acid. Syringic acid was most prominent in the seeds. Although the total flavonoid concentration in the Kei-apple was low, taxifolin and catechin were identified and the seeds almost entirely accounting for these. Conclusion: From this study it was concluded the Kei-apple is a rich source of antioxidant compounds (polyphenols and ascorbate), with a strong antioxidant capacity, and hence may be associated with health promotion properties, particularly in the prevention of cancer, cardiovascular disease, and neurodegeneration. Additionally, due to the increased scientific and commercial interest in this fruit, it is essential to take into consideration the various factors (agronomic, genomic, pre- and post harvest condition and processing) and tissues. This might affect the chemical composition of the final marketed product, which may play a significant role in determining the polyphenol and ascorbate composition and bioactivity of these compounds during food processing procedures. Hence, the polyphenol composition of the various fruit components should be taken into consideration when selecting a method of fruit processing into the desired end product. / Thesis (M.Sc. (Nutrition))--North-West University, Potchefstroom Campus, 2007.

Detecting the presence of insects at low densities can avoid total deterioration of stored grains because corrective actions can be implemented early. Tribolium castaneum (Herbst) and Cryptolestes ferrugineus (Stephens) are the major insect pests of the Canadian grain handling industry. Identification of the volatile organic compounds released by insects can be used to detect insects in stored grains. An attempt was made to identify the volatile organic compounds released by T. castaneum and C. ferrugineus by headspace analysis. The volatiles in the head space of vials with insects, insects and wheat flour, and insects and wheat, were analyzed using a GC-MS coupled with an automatic headspace sampler. Wheat with fifteen percent moisture content was used in this study along with two different insect densities. Feasibility of the automatic headspace sampler in headspace analysis was found to be positive. The sampler can do sample conditioning, absorption, trap cleaning and desorption of the volatiles into the GC-MS and speed up the process. The samples extracted at 20 strokes with 1000 µL per stroke, and desorbed at 250°C gave a clear peak of compounds. The amount of volatiles produced by T. castaneum adults varied based on insect densities, the concentration of Methyl-1, 4-benzoquinone; Ethyl-1, 4-benzoquinone; and 1-Tridecene released by ten adult insects were 355, 390 and 530 µg/L compared to 300,310 and 210 µg/L of Methyl-1, 4-benzoquinone; Ethyl-1, 4-benzoquinone; and 1-Tridecene produced by five adult insects. Extreme high and low temperature leading to death produced very high amounts of volatiles compared to insects kept at 35°C. The larvae of the T. castaneum insects did not produce any volatiles at ambient condition as well as at extreme cold and warm conditions. The C. ferrugineus adults did not produced any detectable amount of volatiles even at the higher insect density after up to 3 days. The results of the combination of T. castaneum and C. ferrugineus insects gave the same volatile organic compounds as produced by T. castaneum insects alone. The 1-Tridecene produced by T. castaneum was not reported previously in other studies.

There is a close relationship between the susceptibility to disease and nutritional state, in the sense that an adequate diet enhances resistance to disease. There is an increasing interest in this beneficial relationship among scientists, food manufacturers and consumers. The trend is moving towards functional foods and their specific health benefits. The results of numerous epidemiological studies and recent clinical trials provide consistent evidence that diets rich in fruits and vegetables can reduce the risk of chronic diseases. These protective effects are mediated through multiple groups of beneficial nutrients contained in the fruits and vegetables, one of these being polyphenol antioxidants. The intake of the polyphenols plays an important role in the reduction and prevention of coronary heart disease (CHD), cardiovascular disease and cancer, as a consequence of their associated antioxidant properties. Fruits contain an array of polyphenols with antioxidant capacity. Polyphenols may be classified in two broad groups namely: flavonoids and non-flavonoids. Flavonoid subgroups in fruits are further grouped as catechins, anthocyanins, procyanidins and flavonol among others. Phenolic acids occur as hydroxylated derivatives of benzoic acid and cinnarnic acid, and are classified as non-flavonoids. Polyphenols have redox properties allowing them to act as reducing agents, hydrogen donators and singlet oxygen quenchers, and thus contribute to the antioxidant capacity of fruits and vegetables. Because of the numerous beneficial effects attributed to these antioxidants, there is renewed interest in finding vegetal species with high phenolic content and relevant biological activities. In view of the importance of these substances towards health and food chemistry, this study will focus on the polyphenol and Vitamin C characterisation and quantification of an indigenous South African fruit, the Kei-apple (Dovyalis cafra), thought to have antioxidant properties. Due to the fact that polyphenol content influences the colour, taste and possible health benefits of the fruit / processed food product, this study will supply valuable information to industry in choosing the best fruit processing methods to attain the desired end product. The exploitation of indigenous South African fruits (Marula and Kei-apple) is receiving increasing prominence, not only due to their health benefits, but also the opportunities these present to rural based economics. Furthermore, this research will serve as a platform for further research on the Kei-apple and other indigenous South African fruits with possible health benefits. Aims: The overall aim of this study is the quantification and characterisation of various nutritionally important antioxidants (polyphenols and ascorbate) in the Kei-apple fruit in its entirety, as well as in its individual fruit components (peel, flesh and seeds). In addition, the total antioxidant capacity of the entire fruit and the various fruit components will be determined in the unfractionated and fractionated fruit extracts. Gas chromatography coupled mass spectrometry (GC-MS) characterisation of the individual polyphenol components will also be analyzed in order to speculate on possible specific health benefits which the Kei-apple may possess. Methods: The study was designed to ensure that a representative fruit sample was collected. Approximately 100 kg Kei-apples were picked in the month of November 2004 from the Bloemhof area in South Africa. A sample of 50 fruits was rinsed and separated into the various components (peel, flesh and seeds). An additional 50 fruits were randomly selected, cleaned and used in their entirety for data representative of the entire fruit. The sample extracts were prepared, after being grounded and lyophilized, by a method described by Eihkonen et al. (1999) using 70% aqueous acetone. The C18-fractionation on the fruit and separated fruit components resulted in four fractions containing (1) phenolic acids; (2) procyanidins, catechins and anthocyanin monomers; (3) flavonols and (4) anthocyanin polymers. The total polyphenol content of the fruit and fruit components as well as the above mentioned C18-fractions were determined by Folin-Ciocalteu's method (Singleton & Rossi, 1965). Both free and total ascorbate concentrations in these samples were determined as described by Beutler (1984), in addition to total sugar content of these via standard methods. Apart from their nutritional interest, both these measurements are necessary for the correction of the total polyphenol concentrations. The total antioxidant capacity of the entire fruit and various fruit components was determined by measuring the oxygen radical absorbance capacity (ORAC) and ferric reducing antioxidant power (FRAP) of the unfractionated and fractionated extracts. Using GC-MS analysis, the various individual polyhenol compounds contributing to the total polyphenol content of the Kei-apple was separated, identified and quantified. This quantitative data was captured and statistically analysed. The analysis of variation was performed using the Tukey Honest Significant Difference test for post-hoc comparison. ORAC, FRAP and polyphenol Pearson correlation analyses were performed using Statistics (Statsoft Inc., Tulsa, Oklahoma, USA) with significance set at P ≤ 0.05. Results and discussion: This study determined the presence of various nutritionally important antioxidants (polyphenols and ascorbate), the total antioxidant capacity in the entire fruit as well as in the individual fruit components (peel, flesh and seeds) and their polyphenol sub group fractions. Total phenol content: The Kei-apple, in its entirety, has a polyphenol concentration of 943 ± 20.3 mg GAE/100g dry weight. Comparison of the individual fruit components showed the seeds to have the highest total polyphenol concentration with 1990 ± 31.3 mg GAE/100g dry weight, followed by that of the peel, 1126 ± 45.8 mg GAE/100g dry weight and then that of the flesh, 521 ± 1.01 mg GAE/100g dry weight. Total, L-ascorbic (ASC) and L-dehydroascobic (DHA) concentration: The total ascorbate of Kei-apple fruit is 517 ± 0.92 mg/100g dry weight. In contrast to the polyphenol content, the flesh of the Kei-apple had significantly the highest concentration of total ascorbate 778 ± 1.20 mg/100g dry weight, Gascorbic 241 ± 21.0 mg/100g dry weight, as well as Gdehydroascobic 537 ± 22.2 mg/100g dry weight. The ratio of Lascorbic acidltotal ascorbate for the flesh, entire fruit, peel and seed is 0.31,0.43,0.49,0.95, respectively, indicating the seeds are the most stable source of biologically active Vitamin C, with 95% of the total ascorbate occurring as G ascorbate. This is also in line with the total polyphenol content of these components, confirming a polyphenol sparing effect on ascorbate. C18-fractionation extracts: Solid phase (C18) fractionation of the Kei-apple fruit and fruit components showed that the fruit, peels and seeds consist predominantly of phenolic acids, followed by procyanidin, catechin and anthocyanin monomers and thereafter varying amounts of anthocyanin polymers and flavonols. Antioxidant capacity: The antioxidant capacity of the entire fruit and individual fruit components as determined by ORAC, (r=0.76) and FRAP, (r=0.95) significantly correlated with the total polyphenol content, as well as to each other (r=0.88), indicating both to be good predictors of antioxidant capacity. GC-MS polyphenol characterisation of the Kei-apple: Caffeic acid and hydro-p-coumaric acid were seen to be the phenolic acids occurring in the highest concentrations in the Kei-apple fruit. The majority of these are concentrated in the flesh and in the case of caffeic acid, also in the peel. The order of predominance of other major non-flavonoid components in the whole fruit analysis are m-hydroxybenzoic acid > p-hydroxyphenyl acetic acid > 3-methoxy-4- hydroxyphenylpropionic acid > p-coumaric acid. The peel of the Kei-apple, apart from caffeic acid, has exceptionally high concentrations of ferulic acid and also serves as a source of protocatechuic acid. Syringic acid was most prominent in the seeds. Although the total flavonoid concentration in the Kei-apple was low, taxifolin and catechin were identified and the seeds almost entirely accounting for these. Conclusion: From this study it was concluded the Kei-apple is a rich source of antioxidant compounds (polyphenols and ascorbate), with a strong antioxidant capacity, and hence may be associated with health promotion properties, particularly in the prevention of cancer, cardiovascular disease, and neurodegeneration. Additionally, due to the increased scientific and commercial interest in this fruit, it is essential to take into consideration the various factors (agronomic, genomic, pre- and post harvest condition and processing) and tissues. This might affect the chemical composition of the final marketed product, which may play a significant role in determining the polyphenol and ascorbate composition and bioactivity of these compounds during food processing procedures. Hence, the polyphenol composition of the various fruit components should be taken into consideration when selecting a method of fruit processing into the desired end product. / Thesis (M.Sc. (Nutrition))--North-West University, Potchefstroom Campus, 2007.

MALDI imaging allows the creation of a molecular image of a tissue slice. This image is reconstructed from the ion abundances in spectra that are obtained while rastering the laser over the tissue. These images can then be correlated with tissue histology to detect potential biomarkers of, for example, aberrant cell types. MALDI is known to have problems with ion suppression, making it difficult to correlate measured ion abundance with concentration. It would be advantageous to have a method that can provide more accurate protein concentration measurements, particularly for screening applications or for precise comparisons between samples. My hypothesis was that a method based on multiple reaction monitoring (MRM) with isotopically-labelled internal standards can be developed which would allow the accurate quantitation of proteins in MALDI Imaging. This study reports on the development of this novel MALDI Imaging method for the localization and accurate quantitation of proteins in tissues. This method involves optimization of in-situ tryptic digestion, followed by reproducible and uniform deposition of an isotopically-labelled standard peptide from a target protein onto the tissue, using an aerosol-generating device. Data is acquired by MALDI-MRM-MS and accurate peptide quantitation is determined from the ratio of MRM transitions for the endogenous unlabelled proteolytic peptides to the corresponding transitions from the applied isotopically-labelled standard peptides. In a parallel experiment, the quantity of the labelled peptide applied to the tissue was determined using a standard curve generated from MALDI-TOF-MS data. This external calibration curve was then used to extrapolate the quantity of endogenous peptide in a given area. All standard curves generated by this method had coefficients of determination greater than 0.97. These proof-of-concept experiments using MALDI MRM-based imaging show the feasibility of obtaining precise and accurate quantitation of tissue protein concentrations over two orders of magnitude, while maintaining the spatial localization information for the proteins. / Graduate

The photodissociation of ozone by ultraviolet light has a great impact on the photochemistry of the atmosphere. The relative quantum yield for the production of the singlet atomic fragment O(¹D) has been determined in the wavelength region 306 to 327 nm for four temperatures between 227 K and 300 K. The technique of resonance enhanced multi photon ionisation (REMPI) was used to probe directly the O(¹D) photolysis product. These relative measurements have been placed onto an absolute scale by the selection of a calibration point whose value has been agreed by the scientific community. The yields obtained are in good agreement with others reported during the time of the research reported in this thesis and clearly show that three mechanisms contribute to the final quantum yield. Below 310 nm, O(¹D) is produced by a spin-allowed channel, above 320 nm the primary channel is a spin- forbidden one and at intermediate wavelengths photolysis of vibrationally excited ozone contributes to the O(¹D) yield. Elements of the quantum yield data presented in this thesis are being included in a new recommendation for the temperature dependent O(¹D) quantum yield. Details of the dissociation kinetics, including further evidence confirming the spin-forbidden channel, is presented in time-of-flight studies of the O(¹D) product. Time-of-flight profiles taken between 317 and 321 nm show evidence that, at room temperature, the O(¹D) quantum yield is anti-correlated with the ozone absorption cross section. Excitation of the O₂(a¹Δ_g) co-fragment has been observed at wavelengths below 296 nm by monitoring the energies of the O(¹D) formed. As the channel for the production of O₂(a¹Δ_g,andnbsp;vandnbsp;=andnbsp;1) opens, it is found that energy is preferentially partitioned into rotation of the O₂ fragment rather than into translation. Initial studies on the O(¹D) fragment have shown that the fragment is orbitally aligned and that the choice of REMPI transition can have a significant effect on the time-of-flight profiles and therefore on the measurements that are made from the profiles. The time-of-flight profiles obtained by probing the O₂(a¹Δ_g) photofragment have shown that the O₂(a¹Δ_g) has an angular momentum polarisation that is J dependent, with the even J being strongly polarised and the odd J depolarised. This results in the shape of the time-of-flight profiles being a function of the REMPI laser polarisation; and the study of this behaviour has been used to confirm the assignments in highly perturbed REMPI spectra.

We have developed novel experiments aimed at understanding whether and how quickly organic aerosols (OA) mix using single-particle mass spectrometry, as different treatments of mixing in regional models significantly affect predicted mass and composition. First, we designed experiments that separate OA formation chemistry from thermodynamics to test whether two populations of particles equilibrate with eachother through the gas phase on experimental timescales. Single-particle mass spectrometry measurements from the aerosol mass spectrometer (AMS) allowed us to quantify the extent of mixing that had occurred. We calibrated this technique using pure-component aerosols with known vapor pressure and phase state, the results of which agreed with a condensation-evaporation model. We then applied these techniques to three atmospherically-relevant situations to determine that: 1) anthropogenic secondary OA (aSOA) does not mix with a surrogate for hydrophobic primary OA (POA), 2) biogenic SOA (bSOA) does not mix with hydophobic POA, and 3) bSOA shows significant mixing with aSOA. The sum of these experiments show that these complex interactions can be measured for atmospherically important systems, a first step towards quantifying activity coefficients for complex OA mixtures. We also investigated mixing within individual particles, using mixed-particles of squalane (a surrogate for hydrophobic POA) and SOA from ↵+pinene + O3 that we determined to contain two separate phases. In these experiments, after formation of the mixed-particles, we perturbed smog chamber with a heat ramp. These data revealed that squalane is able to quickly evaporate from the mixed-particles, and that almost all of the SOA is comprised of material lower in volatility than squalane (a low-volatility constituent of pump oil). For this latter “comparative volatility analysis,” we had to correct for the highly variable collection efficiency (CE) of the mixed particles to correctly calculate the mass fraction of SOA remaining. One of the larger implications of this work is highly dependent on the particle morphology, which we were not able to determine definitively: if indeed the particles are coreshell with squalane inside a thick layer of SOA, our results show that diffusivity within SOA is not ultra-low. Lastly, we present work that furthers our understanding of single-particle CE in the AMS, a quantity especially important for experiments where particle phase is dynamic or there are two separate populations of particles. We report the particle CE of SOA, ammonium sulfate, ammonium nitrate, and squalane. We also determine that half of SOA particles that give meaningful signal, do so at a time later than would be predicted based on their optically-measured flight time through the instrument. We present convincing evidence that the nature of this delay is due to particles ricocheting around the ionization region of the instrument before vaporizing on an auxillary surface near the the vaporizer. This process affects how much mass signal comes from a particle, the particle mass spectrum, and the bulk mass distribution derived from particle time-of-flight mode. Our results also show that while there is no size dependence to CE for SOA, particles that have passed through a thermodenuder have lower CE, implicating oxidation state and/or volatility as a controller of particle bounce.

Studying the intrinsic properties of molecules in the gas-phase is advantageous, since it reduces the complexity present in solution that arises from interactions between the molecule of interest and other species present in the local environment, including those with the solvent itself. In this report, the photophysical properties of gaseous cationic rhodamine B (RBH+) were determined and photodissociation reaction kinetics and power dependence of three prototropic forms of fluorescein; the cation ([F + H]+), monoanion ([F - H]-), and dianion ([F – 2H]-2), each of which possesses their own distinct spectral properties, were measured. The analyte ions of interest were formed via electrospray ionization, mass-selected and stored in a quadrupole ion trap mass spectrometer which has been customized to enable gas-phase spectroscopic studies. Knowledge of the intrinsic photophysical properties of such chromophores in the gas-phase will enable a better understanding of how the local environment of the molecule alters its properties.