Thesis (MScMedSc (Pharmacology))--University of Stellenbosch, 2005. / In this thesis, research results are reported on the role of natural and synthetic surfactants on the in vitro permeability characteristics of various chemical compounds across porcine (buccal, bronchial, arterial, venous and rectal) and human (vaginal) tissues. The permeability flux values of the different compounds (arecoline, 17β-estradiol, hydrocortisone, dexamethasone, vasopressin, oxytocin, zidovudine and isoniazid) were determined using a continuous flow-through diffusion system. Mean steady state flux values were compared statistically by means of a t-test at a significance level of 5% as well as an F-test using whole curve comparisons. The results indicated that the synthetic pulmonary surfactant Biopolsurf is an effective enhancer for the permeation of chemical compounds through most of the tissues tested and that molecular weight, electrostatic charge, partitioning of the molecules in surfactant and surfactant concentration play an important role in trans membrane diffusion. In addition the epithelial permeability of the different types of tissues for various chemical compounds (arecoline, 17β-estradiol, hydrocortisone, dexamethasone, vasopressin and oxytocin) across the above tissues were compared. The results obtained showed that the permeability flux values of the compounds across porcine bronchial and human vaginal tissues were consistently similar and that porcine buccal tissue had the lowest permeability of all tissues tested. This was in agreement with previous in vitro studies. It was concluded that a wide variation in the permeability characteristics of different epithelia exists and that the pulmonary epithelium, due to its high permeability, is probably the most effective epithelium for drug delivery purposes, especially for drugs that undergo extensive gastrointestinal or hepatic first-pass metabolism.

Thesis (PhD (Biochemistry))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Antagonism of antimicrobial action represents an alternative survival strategy for cohabiting soil organisms. Under competitive conditions, our group previously showed that surfactin (Srf) produced by Bacillus subtilis acts antagonistically toward gramicidin S (GS) from a cohabiting bacillus, Aneurinibacillus migulanus, causing the loss the antimicrobial activity of GS. This antagonism appeared to be caused by inactive complex formation. This study aimed to elucidate whether the previously observed antagonism of GS activity by Srf is a general resistance mechanism that also extends to related peptides such as the tyrocidines (Trcs) and linear gramicidins (Grcs) from Bacillus aneurinolyticus. Molecular interaction between the antagonistic peptide pairs was investigated using biophysical analytical methods such as electrospray mass spectrometry (ESMS), circular dichroism (CD), fluorescence spectroscopy (FS) and nuclear magnetic resonance (NMR). Results from this study corroborated the previous findings, namely that Srf antagonised the activity of GS towards Gram positive bacteria. However, for Micrococcus luteus synergism of GS action was observed at low Srf concentrations, while antagonism only occurred at Srf concentrations above the critical micelle concentration (CMC) of Srf when the bacteria were pre-incubated with Srf. This result and an ultra-performance liquid chromatography massspectrometry (UPLC-MS) study indicated that Srf pre-absorbed to cells, as well as Srf micelles interacted with GS, preventing GS from reaching the membrane target. Antagonism of GS action by Srf was also observed towards the Srf producer B. subtilis ATCC21332 and B. subtilis OKB120, a non-producer. The Srf producer was less sensitive than the nonproducer towards GS, possibly due to Srf production. Pre-incubation of Srf at different concentrations caused a dose-dependent antagonism, from as low as 0.9 μM Srf of GS activity towards B. subtilis OKB120. This antagonism at the low Srf concentration may be related to the induction of more resistant biofilms by Srf in B. subtilis. It was also found that Srf significantly improved the survival of B. subtilis OKB120 above that of M luteus in a mixed culture. In addition, the Srf producer B. subtilis ATCC21332 grew in the inhibition zone of the GS producer A. migulanus ATCC9999 during co-culturing, while B. subtilis OKB120 growth was inhibited. Srf induced biofilm formation in B. subtilis may be important in protecting the bacteria in solution, but not on solid phase such as on or in agar plates. Also, the protection of various cell types (previous studies by our group) by Srf from GS indicated a directed antagonistic Srf mode of action. Srf formed complexes that are visible and stable under ESMS conditions with GS, with the peptide bonds in the Val-Orn-Leu-D-Phe moiety of GS and the Val-Asp- D-Leu-Leu moiety of Srf protected from fragmentation. 1H-NMR titration studies strongly indicated that the molecular interaction of Srf and GS involved the re-orientation of the DPhe4,9 and Orn2,7 residues in GS. From CD spectra it was observed that Srf induced a concentration dependent decrease in the β-turn component and increase in β-sheet structures of the GS-Srf mixture. Diffusion orientated NMR (DOSY) indicated that Srf and GS formed homo-oligomers with the Srf-GS mixture having a slightly higher diffusion coefficient indicating the formation of smaller homo-oligomers or more compact hetero-oligomers. These hetero-oligomers involve intermolecular interaction at <5Å between the Orn2,7 residue of GS with Asp residue of Srf, as observed with ROESY-NMR. These results strongly indicate that inactive complex formation between Srf and GS is part of the antagonistic mechanism of action of Srf towards GS. Two high performance liquid chromatography (HPLC) methods was developed to purify peptides from the tyrothricin complex, namely the Trcs (contains one GS Val-Orn-Leu-DPhe- Pro moiety) and Grcs. These peptides were used to assess if Srf has an antagonistic activity beyond that of GS. Srf indeed showed antagonistic action against the antimicrobial activity of Trcs towards B. subtilis ATCC21332 and OKB120, with the tyrocidine C (TrcC) being more sensitive to antagonism than tyrocidine B (TrcB). Srf had an ambiguous effect on the linear gramicidin A (GA) that is co-produced with Trcs in tyrothricin. GA acted synergistically with Srf at low GA concentrations, but slight antagonism was observed at high GA concentrations. In contrast, GA showed pronounced synergism with TrcB towards the M. luteus. However, Srf at 30 μM, antagonised the synergistic action of a lethal mixture of 25 μM GA and TrcB. The Srf producer was also able to withstand and grow in the presence of the tyrothricin producer B. aneurinolyticus ATCC10068, indicating that antagonism of peptide action may allow different organisms to cohabit. Basic NMR and ESMS studies failed to show complex formation between Srf and the Trcs. However, CD presented clear evidence of Srf induced changes in secondary structures and/or higher order self-assembled structures of the Trcs-Srf mixture. FS also provided evidence of the reorientation/exposure of the Trp6 residue of the Trcs in the presence of Srf. These results corroborated the previous findings that complexation between Srf and GS or peptides analogous to GS may be part of the mechanism of Srf antagonistic action. In conclusion, this study showed that the antagonism of GS activity by Srf, conferred in part by inactive complex formation, is a putative resistance mechanism that also extends to other peptides containing the Val-Orn-Leu-D-Phe-Pro moiety such as the Trcs from B. aneurinolyticus. / AFRIKAANSE OPSOMMING: Antagonisme van antimikrobiese aksie verteenwoordig ʼn alternatiewe oorlewingstrategie vir grondorganismes wat in dieselfde habitat gevestig is. Ons groep het gewys dat surfaktien (Srf), geproduseer deur Bacillus subtilis, antagonistiese werking teenoor gramisidien S (GS) vanaf die bacillus Aneurinibacillus migulanus, onder kompeterende kondisies, toon. Die antagonistiese werking, wat moontlik veroorsaak word deur vorming van onaktiewe komplekse, lei tot die verlies van die antimikrobiese aktiwiteit van GS. Hierdie studie se doel was die ontrafeling van die moontlikheid dat die antagonisme van GS aktiwiteit deur Srf, soos deur vorige studies uitgewys, ʼn algemene weerstandsmeganisme is wat moontlik ook verwante peptiede soos die tirosidiene (Trcs) en lineêre gramisidiene (Grcs), afkomstig vanaf Bacillus aneurinolyticus, insluit. In hierdie studie is die molekulêre interaksie tussen antagonistiese peptiedpare ondersoek met biofisiese analitiese metodes wat elektrosproeimassaspektroskopie (ESMS), sirkulêre dichroïsme (SD), fluoressensie-spektroskopie (FS) en kernmagnetiese resonansspektroskopie (KMR) insluit. Die resultate wat tydens hierdie studie verkry is, het gewys dat Srf die werking van GS teenoor Gram-positiewe bakterie teenwerk, en het die vorige waarnemings ondersteun. Daar is egter sinergisme tussen Srf en GS werking by lae Srf-konsentrasies teenoor Micrococcus luteus waargeneem, terwyl antagonisme slegs waargeneem is by Srf-konsentrasies hoër as die kritiese miselêre Srf konsentrasie wanneer bakterieë vooraf met Srf met inkubeer is. Hierdie resultaat, tesame met ʼn ultra-hoë verrigting vloeistofchromatografie gekoppelde massaspektroskopie (UPLC-MS) studie, het daarop gedui dat Srf wat voorheen op selle geabsorbeer het, sowel as Srf-miselle in die media, met GS interaksie het en sodanig kan voorkom dat GS die membraanteiken bereik. Antagonisme deur Srf op die GS aktiwiteit is ook waargeneem teenoor die Srf-produseerder B. subtilis ATCC21332 en B. subtilis OKB120, ʼn nie-produseerder. Hierdie tipe antagonisme by ʼn lae konsentrasie van Srf mag verwant wees aan die induksie van meer weerstandige biofilms deur Srf in B. subtilis. Dit is ook gevind dat Srf die oorlewing van B. subtilis OKB120 aansienlik verhoog teenoor dié van M luteus in ʼn gemengde kultuur. Daar is verder bevind dat die Srf-produseerder, B. subtilis ATCC21332, in die inhibisiesone van die GS-produseerder, A. migulanus ATCC9999, gegroei het tydens kokultivering, terwyl die groei van B. subtilis OKB120 geïnhibeer is. Srf induseer biofilm-vorming in B. subtilis wat moontlik belangrik kan wees om die bakterieë in suspensie te beskerm, maar nie op soliede fase soos byvoorbeeld agar plate nie. Verder dui die beskerming van ʼn verskeidenheid sel-tipes (vorige studies deur ons groep) deur Srf teen GS, ʼn direkte antagonistiese aksie van Srf. Sigbare en stabiele komplekse tussen Srf en GS is waargeneem onder ESMS kondisies, waar die peptiedbindings in die Val-Orn-Leu-D-Phe-Pro eenheid van GS en die Val-Asp-Leu-D-Leu eenheid van Srf beskerm is teen fragmentering in die komplese. 1H-KMR titrasiestudies het duidelik aangetoon dat die molekulêre interaksie van Srf en GS die D-Phe4,9 en Om2, 7 residue in GS heroriënteer. SD-spektra van GS-Srf mengsels het daarop gedui dat Srf ʼn konsentrasieafhanklike vermindering in die β-draai komponente van die mengsel veroorsaak, maar dat β- plaat komponent van die mengsel vermeerder. Diffusie-georiënteerde KMR spektrometrie (DOSY) toon dat Srf en GS homo-oligomere vorm, maar ʼn hoër diffusie koeffisiënt vir die mengsel het aangedui dat die Srf-GS mengsel kleiner of meer kompakte hetero-oligomere. ROESY-KMR toon dat hierdie oligomere intermolekulêre interaksie(s) van <5Å tussen die Om2, 7 residue van GS en die Asp residu van Srf het. Die resultate gee ʼn sterk aanduiding dat die onaktiewe kompleks-vorming tussen Srf en GS deelneem in die antagonistiese werking van Srf teenoor GS. Twee hoë verrigting vloeistofchromatografie metodes is ontwikkel om peptiede uit die tirotrisienkompleks, naamlik die Trcs (bevat een GS Val-Om-Leu-D-Phe-Pro eenheid) en die gramisidiene (Grcs), te suiwer. Hierdie peptiede is gebruik om te bepaal of Srf antagonistiese aktiwiteit het wat verder strek as net dié van GS. Dit was inderdaad die geval en daar is gevind dat Srf antagonisties is teenoor die antimikrobiese aktiwiteit van Trcs met B. subtilis ATCC21332 en OKB120 as teikens, met tirosidien C (TrcC) wat meer sensitief vir antagonistiese werking van Srf was as tyrosidien B (TrcB). Srf het ʼn gemengde effek getoon teenoor lineêre gramisidien A (GA) wat saam met die Trcs in tirotrisien gekoproduseer word. GA het sinergisties met Srf gewerk by lae GA konsentrasies, maar milde antagonistiese werking getoon by hoë GA konsentrasies. Daarteenoor het GA en TrcB uitgesproke sinergisme getoon teenoor M. luteus. In teenstelling het Srf by 30 μM die sinergistiese aksie van die dodelike mengsel van 25 μM GA en TrcB elk geantagoniseer. Die Srf produseerder was ook bestand en kon in die teenwoordigheid van die tirotrisien produseerder B. aneurinolyticus ATCC10068 groei wat aangedui het dat die antagonisme van antibiotiese peptiedaktiwiteit die kohabitasie van organismes toelaat. Basiese KMR en ESMS studies kon nie kompleksvorming tussen Srf en die Trcs aantoon nie, terwyl SD duidelike bewyse gelewer het dat Srf verandering geïnduseer het in die sekondêre strukture en/of hoër orde/self-geassosieerde strukture van die Trc-Srf mengsel. FS het ook bewyse gelewer van die reoriëntasie/blootstelling van die Trp6 residu in die Trcs in die teenwoordigheid van Srf. Hierdie resultate ondersteun die vorige bevindinge dat kompleksvorming tussen Srf en GS of GS-peptiedanaloë deel van die meganisme van Srf se antagonistiese aksie uitmaak. Samevattend het hierdie studie getoon dat die antagonisme van GS aktiwiteit deur Srf deels toegeken kan word aan onaktiewe kompleksvorming tussen die twee peptiede en dat die voorgestelde weerstandsmeganisme ook ander peptiede wat die Val-Orn-Leu-D-Phe-Pro eenheid, soos die Trcs van B. aneurinolyticus, insluit.

In the first phase of the study, the effect of five Safol surfactants on the aqueous solubility of phenanthrene and acenaphthene was determined. The fixed variables were temperature and ionic strength, while surfactant concentration and pH were varied. Quantification of the polyaromatic hydrocarbons (PAHs) was conducted by UV-Visible spectrophotometry. The surfactants had little or no effect on analyte solubilisation below the critical micelle concentration (CMC) while a linear relationship between surfactant concentration and amount of solubilised phenanthrene was observed above CMC concentrations. Safol 45E5 had the highest phenanthrene molar solubilisation ratio (0.83) of the five surfactants tested. The solubilisation of phenanthrene increased marginally (4.1 % for Safol 45E12 and 15.2 % for Safol 45E7) by decreasing the pH from 8 to 5. The concentration of solubilised acenaphthene was 8.4 % higher than phenanthrene in a 1 mM solution of Safol 45E7. The aqueous solubility of phenanthrene was enhanced 11.0, 21.2, 19.6, 15.9 and 14.7 times in 1 mM solutions of Safol 45E3, 45E5, 45E7, 45E9 and 45E12 respectively. Seasand, Longlands sand, Longlands soil and a standard soil sample were spiked with the two PAHs and aged for two weeks. API sludge provided by Sasol and unspiked samples of the above mentioned sorbents were subjected to determinations of organic matter content, particle size distribution and moisture content. The spiked soils and sands and the sludge samples were then washed in various concentrations of Safol 45E7 (0.5, 1.0 and 2.0 mM) at the same temperature used in the solubility studies. A soil mass to solution volume of lg to 10 mL was used. Analyses of the soil and sand samples were conducted by High Pressure Liquid Chromatography (HPLC). Using a 2 mM Safol 45E7 surfactant solution, 100 % and 90 % of phenanthrene and acenaphthene were respectively extracted from Longlands sand and 88 % and 100 % of phenanthrene and acenaphthene were removed from seasand. 8.4 % phenanthrene and 8.17 % of acenaphthene was removed from Longlands soil, while 7.03 % phenanthrene and 6.64 % acenaphthene was removed from the standard soil sample. In the sand desorption studies, the amount of desorbed contaminants initially increased rapidly with increasing surfactant concentration, before levelling off at equilibrium. The amount of desorbed acenaphthene and phenanthrene increased exponentially with increasing surfactant concentration while contaminant concentrations decreased with increasing time in the Longlands soil and standard soil desorption experiments. Dry API sludge samples were also subjected to soil washing studies. The washed samples were Soxhlet extracted and analysed by gas chromatography. The 0.5 mM and 1 mM Safol 45E7 washed sludge samples showed respective phenanthrene peak area percent reductions representing a 44 % and 47 % extraction of phenanthrene from the API sludge. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.

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The manufacture of nonionic surfactants generally involves ethoxylation via ethylene oxide condensation onto a hydrophobe substrate, mostly in the presence of an alkaline catalyst. Nonionic surfactants are used widely in industrial applications, such as detergents, health and personal care, coatings, and polymers. In Australia, approximately one-third of the annual consumption of nonionic surfactants is imported from offshore manufacturers; the market is highly competitive with the local manufacturer facing increasing competition from imports. Optimisation is a pressing need for the current manufacturing plant of the industrial partner for this research project, Huntsman Corporation Australia Pty Limited, the sole domestic manufacturer of nonionic surfactants in Australia. Therefore, the objectives of this research project were to gain a better understanding of the various chemical and physical processes occurring simultaneously in an ethoxylation process; to identify the process limitation in an existing production plant operated by Huntsman Corporation Australia, and to explore measures for enhancing the asset productivity of the production plant. An ethoxylation process working model, describing the chemical kinetics and the physical transport processes involved, was developed to aid the exploration of optimisation opportunities, which would otherwise be empirical. Accordingly, this research project was structured into a two-stage program. The first stage determined the ethoxylation kinetics experimentally. The second stage investigated the interactions of physical transport processes numerically using a computational fluid dynamics (CFD) technique. The manufacturing scheme discussed in this thesis gave particular emphasis to the ethoxylation process operated in semi-batch stirred reactors. In the first stage, a series of kinetic experiments was performed in a well-stirred laboratory autoclave under base-catalysed conditions. The experimental outcomes were developed into a comprehensive kinetic model which took into account the non-ideal features in the reactor operation. Time-dependent physical changes of the reaction system, such as liquid volume, ethylene oxide solubility and density were also included. The ethoxylation behaviour predicted by the model was shown to be in good agreement with the experimental measurements. This indicated that the kinetic model was sufficiently robust to reproduce the reaction behaviour of a commercially operated ethoxylation operation. In the second stage, numerical simulations of an existing ethoxylation reactor system were presented. In addition, two components were addressed: identification of the process limitation and increasing productivity of the industrial-scale ethoxylation plant. An important assumption was made for the ethylene oxide injection system used in this research project which subsequently simplified the ethoxylation system into a single liquid with miscible chemical species. In the identification of the process limitation, three possible rate-limiting factors were examined: mixing, heat removal and reactor pressure rating. Examination and analysis of the physical data available from plant batch reports found that the reactor pressure rating and the presence of nitrogen padding were the rate-limiting factors to the ethoxylation operations in the industrial reactors. It was recommended that the reactor pressure rating be increased to raise the asset productivity of the reactor. In the numerical simulations of the ethoxylation reactor, time-dependent CFD models were developed for two systems: the ethylene oxide injection pipe and the stirred ethoxylation reactors. The heat transfer of ethylene oxide liquid injection was calculated in a two-dimensional model of the dip-leg pipe used in an industrial-scale ethoxylation reactor. The computation gave the temperature of the injection outflow which was validated against the calculated value by empirical correlation. The effects of various surrounding reaction temperatures, injection rates and pipe sizes on the heat transfer rate were investigated. From these, a range of operating conditions yielding a liquid ethylene oxide outflow was selected. Furthermore, it was found that boiling of ethylene oxide was significantly reduced with increasing pipe diameters. It was recommended that the asset productivity of the reactor be improved by keeping more ethylene oxide injected as a liquid in the reaction mixture to raise the reaction rate and shorten the reaction time. Three-dimensional simulations of a baffled reactor agitated by a single- or a dual-Rushton impeller were presented for both non-reactive and reactive flows. Multiple frames of reference and sliding grid methods were used in sequence to describe the relative motion between the rotating impeller and the stationary baffles. The turbulence parameters were modelled with the standard k- � turbulence model. The simulations of non-reactive flow were compared with the literature velocity data obtained from both the experiments and simulations. Good agreement was achieved. The model was then extended to incorporate ethoxylation flow with integration of the kinetics established in the first stage. Both the laboratory autoclave and the industrial-scale reactors were simulated. The former took into account the ethoxylation exotherm and the latter was carried out isothermally. Both simulations were validated against reaction data obtained from physical experiments, either the kinetic experiments or the plant batch productions. The validated model allowed us to determine the optimum operating condition and explore a new reactor system with enhanced asset productivity. A 50% increase in productivity could be accomplished if the ethoxylation was operated closer to the current design pressure limit. Furthermore, the operating pressure of a new reactor system needed to be doubled if the asset productivity were to be increased to approximately three times the current performance.

Nonionic surfactants are commonly used to stabilize proteins during upstream and downstream processing and drug formulation. Surfactants stabilize the proteins through two major mechanisms: (i) their preferential location at nearby interfaces, in this way precluding protein adsorption; and/or (ii) their association with protein into "complexes" that prevent proteins from interacting with surfaces as well as each other. In general, both mechanisms must be at play for effective protein stabilization against aggregation and activity loss, but selection of surfactants for protein stabilization currently is not made with benefit of any quantitative, predictive information to ensure that this requirement is met. In certain circumstances the kinetics of surface tension depression (by surfactant) in protein-surfactant mixtures has been observed to be greater than that recorded for surfactant alone at the same concentration. We compared surface tension depression by poloxamer 188 (Pluronic�� F68), polysorbate 80 (PS 80), and polysorbate 20 (PS 20) in the presence and absence of lysozyme and recombinant protein, at different surfactant concentrations and temperatures. The kinetic results were interpreted with reference to a mechanism for surfactant adsorption governed by the formation of a rate-limiting structural intermediate (i.e., an "activated complex") comprised of surfactant aggregates and protein. The presence of lysozyme was seen to increase the rate of surfactant adsorption in relation to surfactant acting alone at the same concentrations for the polysorbates while less of an effect was seen for Pluronic�� F68. However, the addition of salt was observed to accelerate the surface tension depression of Pluronic�� F68 in the presence of lysozyme. The addition of a more hydrophobic, surface active protein (Amgen recombinant protein) in place of lysozyme resulted in greater enhancement of surfactant adsorption than that recorded in the presence of lysozyme. A simple thermodynamic analysis indicated the presence of protein caused a reduction in ���G for the surfactant adsorption process, with this reduction deriving entirely from a reduction in ���H. We suggest that protein accelerates the adsorption of these surfactants by disrupting their self associations, increasing the concentration of surfactant monomers near the interface. Based on these air-water tensiometry results, it is fair to expect that accelerated surfactant adsorption in the presence of protein (observed with PS 20 and PS 80) will occur with surfactants that stabilize protein mainly by their own adsorption at interfaces, and that the absence of accelerated surfactant adsorption (observed with F68) will be observed with surfactants that form stable surfactant-protein associations. Optical waveguide lightmode spectroscopy was used to test this expectation. Adsorption kinetics were recorded for surfactants (PS 20, PS 80, or F68) and protein (lysozyme or Amgen recombinant protein) at a hydrophilic solid (SiO���-TiO���) surface. Experiments were performed in sequential and competitive adsorption modes, enabling the adsorption kinetic patterns to be interpreted in a fashion revealing the dominant mode of surfactant-mediated stabilization of protein in each case. Kinetic results confirmed predictions based on our earlier quantitative analysis of protein effects on surface tension depression by surfactants. In particular, PS 20 and PS 80 are able to inhibit protein adsorption only by their preferential location at the interface, and not by formation of less surface active, protein-surfactant complexes. On the other hand, F68 is able to inhibit protein adsorption by formation of protein-surfactant complexes, and not by its preferential location at the interface. / Graduation date: 2013 / Access restricted to the OSU Community at author's request from Sept. 24, 2012 - Feb. 24, 2013.

This work concerns the efficient treatment of wastewaters from pulp and paper mills by means of aerobic biological processes. For treatment processes there are many aspects of efficiency and the present study investigates both energy efficiency and purification efficiency during disturbances. Special focus is put on wood extractives, such as resin acids and fatty acids, since they can cause negative effects in fish and other organisms in the receiving waters. They can furthermore be toxic to microorganisms in a biological treatment plant. They also affect oxygen transfer, which is important for energy efficient aeration of aerobic biological treatment processes. This thesis includes five papers/studies and presents a strategy for efficient treatment of forest industrial wastewaters. The results should help creating resilient wastewater treatment strategies with efficient use of energy. One new strategy proposed here includes separation of extractives before the wastewater is treated biologically, and the use of the extra amount of sludge as an energy source, shifting the energy balance from negative to positive.

In particle induced desorption-ionization mass spectrometry the strength of an analyte's signal under a given set of bombardment conditions is usually considered to be representative of the analytes relative surface activity. This rationale is generally used to explain differences in the technique's sensitivity between and within various classes of compound. In liquid matrix assisted secondary ion mass spectrometry (SIMS) sensitivity enhancement of ionic analytes by pairing with surface active counterions has been demonstrated by several groups. This technique has been utilized in this work to achieve a 10,000 fold enhancement in the signal for ATP on a double focusing magnetic sector instrument and to detect femtomole quantities of nucleoside monophosphates on a time-of-flight instrument. The analyte's signal, however, is dependent on both the analyte bulk concentration and that of the surfactant. Additionally, the surfactant concentration that produces the maximum analyte signal changes with the analyte concentration. In this study, this phenomenon has been modeled in terms of conventional solution equilibria and surface chemical principles. It is assumed that the initial surface composition and the bulk concentration are the boundary conditions of a steady state established by the competing processes of surface sputtering and surface replenishment from the bulk during analysis. Calculated surface excesses correlate well with observed relative ion intensities, suggesting that equilibrium conditions are approached in the sample matrices despite the outwardly dynamic nature of the sputtering processes. / Graduation date: 1994