Surfactants can be extremely toxic to aquatic species and are introduced to the environment in a variety of ways. It is thus important to understand how other environmental constituents, in this case humic acids (HAs), may alter the toxicity of anthropogenic surfactants. Hatching and mortality assays of Artemia Franciscana were performed for three different toxic surfactants: Triton X-100 (Tx-100, non-ionic), cetylpyridinium chloride (CPC, cationic), and sodium dodecyl sulfate (SDS, anionic). Humic acids of varying composition and concentrations were added to the assays to determine the toxicity mitigating ability of the HAs. Tx-100 had a significant toxic effect on Artemia mortality rates and HAs from terrestrial sources were able to mitigate the toxicity, but an aquatic HA did not. CPC and SDS limited hatching success of the Artemia and, as HAs were added, the hatching percentages increased for all HA sources, indicating toxicity mitigation. In order to determine which functional groups within HAs were responsible for the interaction with the surfactants, the HAs were chemically modified by: (i) bleaching to reduce aromatics, (ii) Soxhlet extraction to reduce lipids, and (iii) acid hydrolysis to reduce O- and N-alkyl groups. Although most of the modified HAs had some toxicity mitigating ability for each of the surfactants, there were two notable differences: 1) the lipid-extracted HA did not reduce the toxicity of Tx-100 and 2) the bleached HA had a lower toxicity mitigating ability for CPC than the other modified HAs.

A set of low-sulfur diesel fuels from the Western Pacific region were found to be unstable during storage although they passed all standard specification tests. This sample set was found to have high nitrogen content. Initially, liquid–liquid extractions with a mild aqueous acid were performed to separate basic and nonbasic nitrogen groups in an attempt to determine if these organonitrogen classes were responsible for the poor stability. The findings of this study indicate that there may be a correlation between the acid-extractable nitrogen compounds in these fuels and the formation of high levels of particulates in storage. To develop a more comprehensive understanding of the classes and distributions of organonitrogen compounds in fuels, a novel analytical method was developed using two-dimensional gas chromatography with nitrogen chemiluminescence detection (GCxGC-NCD). The GCxGC-NCD analyses revealed the presence of three distinct groups of nitrogen compounds. One group corresponded to the acid-extractable basic nitrogen compounds, one with the nonbasic nitrogen compounds, and a third early-eluting lighter polar organonitrogen fraction that had previously not been observed. This light organonitrogen fraction was unique to these particularly unstable fuels. If this is found to be universally applicable, this light polar nitrogen fraction may serve as an indicator of potentially unstable diesel fuels. Overall, the GCxGC-NCD method has been shown to be a valuable tool to enhance our understanding of the chemistry of organonitrogen species and their impact on fuel stability.

A semiqualitative and quantitative method was developed to classify and quantify nitrogen-containing compounds (NCCs) in aviation and diesel fuels and marine gas oils by using two-dimensional gas chromatography with a nitrogen chemiluminescence detector (GCxGC NCD) without the need for lengthy extractions. Homoscedasticity was evaluated for different forms of linear regression. The weighted (1/x) trend line was more accurate than the nonweighted and weighted (1/x2) trend lines when quantitating six mixtures composed of several NCCs ranging from 50 ppb to 50 ppm. The lower limits of detection and quantitation of nitrogen were 6 and 20 ppb, respectively, by using the weighted (1/x) trend line. Relative response factors (RRF) of nitrogen were measured for several compounds, which showed that several aromatic (aniline, quinoline, benzothiazole, o-anisidine, and carbazole) and nonaromatic (N,N-dimethyldecylamine and N,N-dimethyldodecylamine) compounds have similar responses. Conversely, pyridine and pyrrole have smaller RRF. Further, alkylated pyridine and pyrrole were shown to have greater RRF than pyridine and pyrrole. Hence, equimolar responses for different NCCs were not observed in this study. Small RRF were likely not the result of thermally-induced degradation of analytes upon entry into the GC inlet. The elution times of known compounds were repeatable, which enabled the production of a template composed of chromatographic bins that facilitated characterization and quantitation of unknown NCCs in fuel samples. The template advances the classification of unknown NCCs in fuels compared to simplified classifications as basic, nonbasic, and neutral. Clear differences were observed in the chemical composition and concentrations of NCCs when the disparate fuel types were compared and between the same type of fuels (i.e., aviation fuels). Interday quality control measurements demonstrated high repeatability. Overall, the GCxGC NCD method was shown to be robust, repeatable, facilitated high throughput chemical analysis without the need for extractions, and provided detailed compositional and quantifiable data. This information may aid in linking correlations between NCCs and fuel properties such as stability.

Surfactants, such as triton X-100 (Tx-100), cetylpyridinium chloride (CPC), and sodium dodecyl sulfate (SDS) are known to be toxic to Artemia Franciscana (Artemia) – an organism, frequently used to monitor the health of the aquatic environment. The phospho-metabolite profile of a living organism is often indicative of imbalances that may have been caused by environmental stressors, such as surfactants. This study utilizes i n vivo 31P NMR to monitor temporal changes in the phospho-metabolite profile of Artemia caused by Tx-100, CPC, and SDS and the ability of humic acid (HA) to mitigate the toxicity of these surfactants. It was found that, while Tx-100 does not have any effect on the phospho-metabolite profile, both CPC and SDS cause a complete retardation in growth of the phosphodiester (PDE) peak in the 31P NMR spectrum, which is indicative of the inhibited cell replication. This growth inhibition was independently verified by the decreased guanosine triphosphate (GTP) concentration in the CPC and SDS-exposed Artemia. In addition, upon introduction of HA to the CPC and SDS-exposed Artemia, an increase of PDE peak over time is indicative of HA mitigating toxicity.

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