Effects of Environmentally Relevant Concentration Exposure Profiles on Polar Organic Chemical Integrative Sampler (POCIS) Sampling Rates.

Polar organic chemical integrative sampler (POCIS) is a passive sampling device that offers many advantages over traditional discrete sampling methods, but quantitative time-weighted average (TWA) concentrations rely heavily on the robustness of sampling rates. The effects of changing chemical concentration exposures on POCIS sampling rates and its ability to operate in an integrative regime were investigated for 12 pesticides across a range of environmentally relevant concentrations. In five independent 21-day experiments, POCIS devices were exposed to these compounds at constant concentrations ranging from 3 to 60 µg/L and multiple pulsed concentrations with maximum peaks ranging from 5 to 150 µg/L (TWA concentrations = 3 to 92 µg/L). For the 21-day exposures to constant and pulsed concentrations, there were no significant differences in the POCIS sampling rates between corresponding TWA concentrations. Similarly, there was no significant effect on POCIS ability to operate in an integrative regime. However, loss of linearity was visible for some replicates when exposed to higher pulsed concentrations over an extended period. Modeling and Freundlich isotherms did not predict sorbent saturation, but the extraction and reconstitution protocol likely contributed to atrazine dissolution and subsequent underestimation of sorbed chemical mass when HLB adsorption exceeded 400 µg.

The evolution of total internal reflection Raman spectroscopy for the chemical characterization of thin films and interfaces.

Total internal reflection (TIR) optical spectroscopies have been widely used for decades as non-destructive and surface-sensitive measurements of thin films and interfaces. Under TIR conditions, an evanescent wave propagates into the sample layer within a region approximately 50 nm to 2 µm from the interface, which limits the spatial extent of the optical signal. The most common TIR optical spectroscopies are fluorescence (i.e., TIRF) and infrared spectroscopy (i.e., attenuated total reflection infrared). Despite the first report of TIR Raman spectroscopy appearing in 1973, this method has not received the same attention to date. While TIR Raman methods can provide chemical specific information, it has been outshined in many respects by surface-enhanced Raman spectroscopy (SERS). TIR Raman spectroscopy, however, is garnering more interest for analyzing the chemical and physical properties of thin polymer films, self-assembled monolayers (SAMs), multilayered systems, and adsorption at an interface. Herein, we discuss the early experimental and computational work that laid the foundation for recent developments in the use of TIR Raman techniques. Recent applications of TIR Raman spectroscopy as well as modern TIR Raman instruments capable of measuring monolayer-sensitive vibrational modes on smooth metallic surfaces are also discussed. The use of TIR Raman spectroscopy has been on a rise and will continue to push the limits for chemical specific interfacial and thin film measurements. Graphical abstract Total internal reflection (TIR) Raman spectroscopy can extract the chemical and physical information from thin films and adsorbates.

Combined measurement of directional Raman scattering and surface-plasmon-polariton cone from adsorbates on smooth planar gold surfaces.

Directional-surface-plasmon-coupled Raman scattering (directional RS) has the combined benefits of surface plasmon resonance and Raman spectroscopy, and provides the ability to measure adsorption and monolayer-sensitive chemical information. Directional RS is performed by optically coupling a 50 nm gold film to a Weierstrass prism in the Kretschmann configuration and scanning the angle of the incident laser under total internal reflection. The collected parameters on the prism side of the interface include a full surface-plasmon-polariton cone and the full Raman signal radiating from the cone as a function of incident angle. An instrument for performing directional RS and a quantitative study of the instrumental parameters are herein reported. To test the sensitivity and quantify the instrument parameters, self-assembled monolayers and 10 to 100 nm polymer films are studied. The signals are found to be well-modeled by two calculated angle-dependent parameters: three-dimensional finite-difference time-domain calculations of the electric field generated in the sample layer and projected to the far-field, and Fresnel calculations of the reflected light intensity. This is the first report of the quantitative study of the full surface-plasmon-polariton cone intensity, cone diameter, and directional Raman signal as a function of incident angle. We propose that directional RS is a viable alternative to surface plasmon resonance when added chemical information is beneficial.

Fourier transform-plasmon waveguide spectroscopy: a nondestructive multifrequency method for simultaneously determining polymer thickness and apparent index of refraction.

Fourier transform (FT)-plasmon waveguide resonance (PWR) spectroscopy measures light reflectivity at a waveguide interface as the incident frequency and angle are scanned. Under conditions of total internal reflection, the reflected light intensity is attenuated when the incident frequency and angle satisfy conditions for exciting surface plasmon modes in the metal as well as guided modes within the waveguide. Expanding upon the concept of two-frequency surface plasmon resonance developed by Peterlinz and Georgiadis [Opt. Commun. 1996, 130, 260], the apparent index of refraction and the thickness of a waveguide can be measured precisely and simultaneously by FT-PWR with an average percent relative error of 0.4%. Measuring reflectivity for a range of frequencies extends the analysis to a wide variety of sample compositions and thicknesses since frequencies with the maximum attenuation can be selected to optimize the analysis. Additionally, the ability to measure reflectivity curves with both p- and s-polarized light provides anisotropic indices of refraction. FT-PWR is demonstrated using polystyrene waveguides of varying thickness, and the validity of FT-PWR measurements are verified by comparing the results to data from profilometry and atomic force microscopy (AFM).

Suspect and non-target screening of acutely toxic Prymnesium parvum.

Harmful algal blooms (HABs) are increasing in frequency, magnitude, and duration around the world. Prymnesium parvum is a HAB species known to cause massive fish kills, but the toxin(s) it produces contributing to this acute toxicity to fish have not been confirmed. In the present study, a 2 × 2 factorial design was employed to examine influences of salinity (2.4 or 5 ppt) and nutrient limitation (f/2 or f/8) on P. parvum acute toxicity to fish and produced molecules. Acute toxicity (LC50) of these cultures, following a 48-h mortality assay, ranged from 10,213 to 96,816 cells mL-1. Non-targeted analysis was performed using liquid chromatography high-resolution mass spectrometry (LC-HRMS) to investigate compounds contributing to the differential toxicological responses. When P. parvum elicited toxicity to fish, suspect screening confirmed the presence of several prymnesins, and the peak area of PRM-A (3 Cl; prymnesin2aglycone) was significantly (p < 0.05) and positively related to acute toxicity. In addition, a non-targeted approach to highlighting peaks that differ between two chemical fingerprints was developed, termed a relative difference plot, and used to search for peaks co-varying with P. parvum induced acute toxicity to fish. Several peaks were highlighted along with the prymnesins identified through suspect screening when acute toxicity to fish was observed.

Determination of microcystins, nodularin, anatoxin-a, cylindrospermopsin, and saxitoxin in water and fish tissue using isotope dilution liquid chromatography tandem mass spectrometry.

Cyanobacteria can form dense blooms under specific environmental conditions, and some species produce secondary metabolites known as cyanotoxins, which present significant risks to public health and the environment. Identifying toxins produced by cyanobacteria present in surface water and fish is critical to ensuring high quality food and water for consumption, and protectionn of recreational uses. Current analytical screening methods typically focus on one class of cyanotoxins in a single matrix and rarely include saxitoxin. Thus, a cross-class screening method for microcystins, nodularin, anatoxin-a, cylindrospermopsin, and saxitoxin was developed to examine target analytes in environmental water and fish tissue. This was done, due to the broad range of cyanotoxin physicochemical properties, by pairing two extraction and separation techniques to improve isolation and detection. For the first time a zwitterionic hydrophilic interaction liquid chromatography column was evaluated to separate anatoxin-a, cylindrospermopsin, and saxitoxin, demonstrating greater sensitivity for all three compounds over previous techniques. Further, the method for microcystins, nodularin, anatoxin-a, and cylindrospermopsin were validated using isotopically labeled internal standards, again for the first time, resulting in improved compensation for recovery bias and matrix suppression. Optimized extractions for water and fish tissue can be extended to other congeners in the future. These improved separation and isotope dilution techniques are a launching point for more complex, non-targeted analyses, with preliminary targeted screening.

Large-Scale Synthesis of Colloidal Si Nanocrystals and Their Helium Plasma Processing into Spin-On, Carbon-Free Nanocrystalline Si Films.

This paper describes a simple approach to the large-scale synthesis of colloidal Si nanocrystals and their processing into spin-on carbon-free nanocrystalline Si films. The synthesized silicon nanoparticles are capped with decene, dispersed in hexane, and deposited on silicon substrates. The deposited films are exposed to nonoxidizing room-temperature He plasma to remove the organic ligands without adversely affecting the silicon nanoparticles to form crack-free thin films. We further show that the reactive ion etching rate in these films is 1.87 times faster than that for single-crystalline Si, consistent with a simple geometric argument that accounts for the nanoscale roughness caused by the nanoparticle shape.

Calcination does not remove all carbon from colloidal nanocrystal assemblies.

Removing organics from hybrid nanostructures is a crucial step in many bottom-up materials fabrication approaches. It is usually assumed that calcination is an effective solution to this problem, especially for thin films. This assumption has led to its application in thousands of papers. We here show that this general assumption is incorrect by using a relevant and highly controlled model system consisting of thin films of ligand-capped ZrO2 nanocrystals. After calcination at 800 °C for 12 h, while Raman spectroscopy fails to detect the ligands after calcination, elastic backscattering spectrometry characterization demonstrates that ~18% of the original carbon atoms are still present in the film. By comparison plasma processing successfully removes the ligands. Our growth kinetic analysis shows that the calcined materials have significantly different interfacial properties than the plasma-processed counterparts. Calcination is not a reliable strategy for the production of single-phase all-inorganic materials from colloidal nanoparticles.

High angular-resolution automated visible-wavelength scanning angle Raman microscopy.

A scanning angle (SA) Raman microscope with 532-nm excitation is reported for probing chemical content perpendicular to a sample interface. The instrument is fully automated to collect Raman spectra across a range of incident angles from 20.50 to 79.50° with an angular spread of 0.4±0.2° and an angular uncertainty of 0.09°. Instrumental controls drive a rotational stage with a fixed axis of rotation relative to a prism-based sample interface mounted on an inverted microscope stage. Three benefits of SA Raman microscopy using visible wavelengths, compared to near infrared wavelengths are: (i) better surface sensitivity; (ii) increased signal due to the frequency to the fourth power dependence of the Raman signal, and the possibility for resonant enhancement; (iii) the need to scan a reduced angular range to shorten data collection times. These benefits were demonstrated with SA Raman measurements of thin polymer films of polystyrene or a diblock copolymer of polystyrene and poly(3-hexylthiophene-2,5-diyl). Thin film spectra were collected with a signal-to-noise ratio of 30 using a 0.25 s acquisition time.

Diastereoselective discrimination of lysine-alanine-alanine peptides by zwitterionic cinchona alkaloid-based chiral selectors using electrospray ionization mass spectrometry.

Electrospray ionization-mass spectrometry (ESI-MS) was used to investigate stereoselective interactions between seven zwitterionic alkylsulfonate-modified cinchona alkaloid chiral selectors and biologically relevant lysine-alanine-alanine tripeptide and alanine-alanine dipeptide selectands in modified methanolic solutions. Ion intensities from full scan mass spectra were used to assess degrees of association, the ratios of which were used to calculate selectivities for different selector-selectand pairs. The results support prior work on similar systems using HPLC, in that binding is mediated in these systems primarily through the quinuclidine amine on the selector and the C-terminal carboxylate of the peptide. N(α)- and N(α), N(ɛ)-acetylated forms of the tripeptide were used to study the relative contribution to binding imparted by the presence of multiple basic amines on the tripeptide with the selectors; this was not previously investigated by HPLC. The ability of the sulfonate group on the selector to reach and preferentially interact with the N(ɛ)-amine on the side chain of lysine was revealed. Overall, in acidic methanol conditions (0.5% acetic acid), degrees of association ranged from 1.5% to 17%, and selectivities ranged from non-selective to a 5.5:1 preference for binding one peptide stereoisomer over another with a given chiral selector. In sodium acetate (100 µM)-modified methanol solutions, significant changes in degrees of association (ranging from 4% to 25%) and selectivities (ranging from non-selective to 4.2:1 preference) were observed. These mass spectrometry experiments help to clarify the chiral recognition mechanism for these selectors and suggest that retention and selectivity could be further modulated in HPLC experiments through the utilization of alkali salt-containing mobile phases.