A comparison of frontal and nonfrontal methods for determining solid-liquid adsorption isotherms using inverse liquid chromatography

A promising sensing platform for explosive markers: Zeolite-like metal-organic framework based monolithic composite as a case study

Preconcentration for on-site detection or subsequent determination is a promising technique for selective sensing explosive markers at low concentrations. Here, we report divinylbenzene monolithic polymer in its blank form (neat-DVB) and as a composite incorporated with sodalite topology zeolite-like metal-organic frameworks (3-ZMOF@DVB), as a sensitive, selective, and cost-effective porous preconcentrator for aliphatic nitroalkanes in the vapor phase as explosive markers at infinite dilution. The developed materials were fabricated as 18 cm gas chromatography (GC) monolithic capillary columns to study their separation performance of nitroalkane mixture and the subsequent physicochemical study of adsorption using the inverse gas chromatography (IGC) technique. A strong preconcentration effect was indicated by a specific retention volume adsorption/desorption ratio equal to 3 for nitromethane on the neat-DVB monolith host-guest interaction, and a 14% higher ratio was observed using the 3-ZMOF@DVB monolithic composite despite the low percentage of 0.7 wt.% of sod-ZMOF added. Furthermore, Incorporating ZMOF resulted in a higher percentage of micropores, increasing the degree of freedom more than bringing stronger adsorption and entropic-driven interaction more than enthalpic. The specific free energy of adsorption (ΔGS) values increased for polar probes and nitroalkanes, denoting that adding ZMOFs earned the DVB monolithic matrix a more specific character. Afterward, Lewis acid-base properties were calculated, estimating the electron acceptor (KA) and electron donor (KB) constants. The neat-DVB was found to have a Lewis basic character with KB/KA = 7.71, and the 3-ZMOF@DVB had a less Lewis basic character with KB/KA = 3.82. An increased electron-accepting nature can be directly related to incorporating sod-ZMOF into the DVB monolithic matrix. This work considers the initial step in presenting a portable explosives detector or preconcentrating explosive markers trace prior to more sophisticated analysis. Additionally, the IGC technique allows for understanding the factors that led to the superior adsorption of nitroalkanes for the developed materials.

Inverse liquid-solid chromatography to evaluate drug interactions with organosilane-modified polydimethylsiloxane for use in body-on-a-chip systems

Body-on-a-chip and organ-on-a-chip systems utilize polydimethylsiloxane (PDMS) because of the relative suitability of the material for fabrication of microfluidic channels and chambers used in these devices. However, hydrophobic molecules, especially therapeutic compounds, tend to adsorb to PDMS, which may distort the dose-response curves that feed into the pharmacokinetic/pharmacodynamic models used to translate preclinical data into predictions of clinical outcomes. Surface modification by organosilanes is one method being explored to modify PDMS, but the effect of organosilanes on drug adsorption isotherms is not well characterized. We utilized Inverse Liquid-Solid Chromatography to characterize the adsorption parameters of the drugs acetaminophen, diclofenac, and verapamil with native PDMS and organosilane-modified (fluoropolymer (13F) and polyethylene glycol) PDMS surfaces, to correlate the modifications with changes in drug adsorption. It was determined that the organosilane modifications significantly changed the energy of adsorption of the test drug utilizing our methodology.

Retention characteristics of silica materials in carbon dioxide/methanol mixtures studied by inverse supercritical fluid chromatography

In this work, inverse supercritical fluid chromatography was applied to characterize the surface of four silica materials (three commercial Kromasils and one silica aerogel) from chromatographic retention data. Retention factors at various pressures (150-300 bar), temperatures (25-60 °C) and modifier concentrations (5-20 vol.% methanol in CO₂) for a set of representative 17 solutes were correlated with the solute properties by the linear solvation energy relationships (LSER). Two types of the LSER models were identified based on different criteria. Firstly, a generally valid model with two descriptors concerning dipolarity/polarizability and solute hydrogen-bonding acceptor ability was constructed. Secondly, a group of specific models for each particular silica material was proposed. According to the statistical analysis of the modeling results, the acid-basic interactions were demonstrated to have a major contribution to the retention for all studied silicas. The intensity of these interactions decreases with increasing methanol concentration in the mobile phase, possibly due to the mixed mechanism of competitive adsorption of the modifier on silanol groups and modification of mobile phase property. Moreover, retention factors measured under constant conditions (p, T, methanol concentration) for a pair of the materials were found to be proportional in logarithmic scale implying the transferability of the adsorption free energies and the adsorption constants across four studied silica materials.

The accurate measurement of second virial coefficients using self-interaction chromatography: experimental considerations

Measurement of B22, the second virial coefficient, is an important technique for describing the solution behaviour of proteins, especially as it relates to precipitation, aggregation and crystallisation phenomena. This paper describes the best practise for calculating B22 values from self-interaction chromatograms (SIC) for aqueous protein solutions. Detailed analysis of SIC peak shapes for lysozyme shows that non-Gaussian peaks are commonly encountered for SIC, with typical peak asymmetries of 10%. This asymmetry reflects a non-linear chromatographic retention process, in this case heterogeneity of the protein-protein interactions. Therefore, it is important to use the centre of mass calculations for determining accurate retention volumes and thus B22 values. Empirical peak maximum chromatogram analysis, often reported in the literature, can result in errors of up to 50% in B22 values. A methodology is reported here for determining both the mean and the variance in B22 from SIC experiments, includes a correction for normal longitudinal peak broadening. The variance in B22 due to chemical effects is quantified statistically and is a measure of the heterogeneity of protein-protein interactions in solution. In the case of lysozyme, a wide range of B22 values are measured which can vary significantly from the average B22 values.

Inverse gas chromatographic method for measuring the dispersive surface energy distribution for particulates

Inverse gas chromatography (IGC) is a widely used method for determining the dispersive component of the surface energy (gamma s (d)) of particulate and fibrous solids. Such measurements are normally conducted at very low solute concentrations (infinite dilution), and they result in a single numerical value of gamma s (d) for homogeneous materials which exhibit Henry's Law adsorption behavior. However, many real solid surfaces are heterogeneous and this may be demonstrated by the nonlinear isotherms obtained at low solute surface coverages resulting in reported gamma s (d) values which are not unique. This paper presents a new method for determining of gamma s (d) distributions as a function of the solute surface coverage using adsorption isosteres for an homologous series of hydrocarbon adsorbates. gamma s (d) distributions reported here were successfully determined using two different solid materials (glass beads and alumina particles) up to typical surface coverages of approximately 10% and clearly show significant variations in gamma s (d) with solute surface coverage. The effects of sample aging and pretreatment also exhibited clear differences in the gamma s (d) distributions obtained. gamma s (d) was determined using both the Dorris-Gray and Schultz methods, with the Dorris-Gray method exhibiting a much lower experimental error. It was established that the errors associated with this statistical measurement of surface energy were strongly dependent on the quality of the experimental data sets obtained. R (2) for the linearity of fit of the retention data to the Dorris-Gray gamma s (d) analysis was found to be a valid criterion for predicting the robustness of gamma s (d) distributions obtained. Detailed discussions of other critical experimental and analysis factors relevant to this methodology, as well as the reproducibility of gamma s (d) profiles are also presented. This paper establishes that IGC can be used for determining the gamma s (d) distributions of particulate solids and is demonstrated that this method is very useful way for studying the surface energy heterogeneity of complex particulate solids.