The sonication-centrifugation technique is commonly used for dispersing single-walled carbon nanotubes (SWCNTs) in aqueous surfactant solutions. However, the methodologies and materials used for this purpose are widely varied, and few dispersive agents have been studied systematically. This work describes a systematic study into the ability of some well-known (and some less common) surfactants and polymers to disperse SWCNTs fabricated by two different techniques. UV-vis-NIR absorbance spectra of their supernatant solutions showed that the smaller ionic surfactants were generally more effective dispersants, with larger polymer and surfactant molecules exhibiting a reduced performance for ensembles of carbon nanotubes of smaller average diameter. Optimal surfactant concentrations were established for dispersions of carbon nanotubes produced by the electric arc method in aqueous solutions of sodium dodecylbenzene sulfonate, sodium deoxycholate, Triton X-405, Brij S-100, Pluronic F-127, and polyvinylpyrrolidone. This optimum value was determined as the point at which the relative concentration of nanotubes dispersed is maximized, before flocculation-inducing attractive depletion interactions begin to dominate. The aggregation state of carbon nanotubes dispersed in sodium dodecylbenzene sulfonate was probed by AFM at different stages of rebundling, showing the length dependence of these effects.

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In the postmortem environment, some drugs and metabolites may degrade due to microbial activity, even forming degradation products that are not produced in humans. Consequently, underestimation or overestimation of perimortem drug concentrations or even false negatives are possible when analyzing postmortem specimens. Therefore, understanding whether medications may be susceptible to microbial degradation is critical in order to ensure that reliable detection and quantitation of drugs and their degradation products is achieved in toxicology screening methods. In this study, a “simulated postmortem blood” model constructed of antemortem human whole blood inoculated with a broad population of human fecal microorganisms was used to investigate the stability of 17 antidepressant and antipsychotic drugs. Microbial communities present in the experiments were determined to be relevant to postmortem blood microorganisms by 16S rRNA sequencing analyses. After 7 days of exposure to the community at 37°C, drug stability was evaluated using liquid chromatography coupled with diode array detection (LC‐DAD) and with quadrupole time‐of‐flight mass spectrometry (LC‐QTOF‐MS). Most of the investigated drugs were found to be stable in inoculated samples and noninoculated controls. However, the 1,2‐benzisothiazole antipsychotics, ziprasidone and lurasidone, were found to degrade at a rate comparable with the known labile control, risperidone. In longer experiments (7 to 12 months), where specimens were stored at −20°C, 4°C, and ambient temperature, N‐dealkylation degradation products were detected for many of the drugs, with greater formation in specimens stored at −20°C than at 4°C.

Current methods of synthesis for carbon nanotubes (CNTs) usually produce heterogeneous mixtures of different nanotube diameters and thus a mixture of electronic properties. Consequently, many techniques to sort nanotubes according to their electronic type have been devised. One such method involves the chemical reaction of CNTs with aryl diazonium salts. Here we examine the reactions of electric arc produced CNTs (dispersed by a variety of surfactants and polymers in aqueous solution) with 4-bromo-, 4-nitro-, and 4-carboxybenzenediazonium tetrafluoroborate salts in order to find conditions for maximum selectivity. Reactions were monitored through the semiconducting S22 and metallic M11 transitions in the UV–vis–NIR absorbance spectra of the nanotube dispersions. Selectivity was observed to depend heavily on the type of surfactant, the type of diazonium salt and its concentration, the reaction temperature, and the solution pH. Additionally, the surfactant concentration was found to exert a significant influence as the dediazoniation product yields are affected by this parameter. For certain combinations of surfactant and diazonium salt the selectivity is markedly improved, particularly in dispersions of nonionic surfactants Pluronic F-127 and Brij S-100, which are similar in structure. Smaller diameter HiPCO nanotubes were better functionalized in dispersions of Triton X-405. The greater selectivity afforded by these poly(ethylene oxide) containing polymers is postulated to arise from electron donation provided by their ether oxygens. The ionic surfactant sodium dodecyl sulfate was found to display unique behavior in that semiconducting nanotubes were preferentially functionalized at natural pH, likely due charge localization interactions with the surfactant.