The binding affinity of uncharged aromatic solutes for negatively charged resins is enhanced by cations via cation–π interactions: The case of sodium ion and arginine

Mixed-mode chromatography of mixed functionalized analytes as the homologues of benzalkonium chloride. Application to pharmaceutical formulations

In this work, a retention behavior based on mixed-mode reversed-phase (RP)/hydrophilic interaction liquid chromatography (HILIC) was observed for benzalkonium chloride (BAK) using a core-shell column functionalized with biphenyl groups. Although in the literature, the U-shaped retention was reported for polar compounds in mixed functionalized phases, in the present work, the behavior was dependent upon the chemical structure of the analyte with mixed functionality (ammonium group, a benzyl group and an alkyl chain) and on the high selectivity of the chromatographic column. The bimodal retention was observed for the four BAK homologues using a content of acetonitrile from 65 to 95% in the mobile phase. The data were adjusted to polynomial equations which allow for modeling and predicting the U-shaped retention. The salt concentration (50 and 100 mM), anion (formate and acetate) and cation (ammonium and triethylammonium) of the salt, pH (4 and 5) in the mobile phase were studied in order to understand their influence on the two retention modes. Significant electrostatic interactions were involved in the two retention modes, especially with a content of acetonitrile higher that 90%. Linear relationships between the retention factors of the four homologues were found in a wide range of %acetonitrile when the salt and triethylamine concentration, pH and nature of salt were changed. The differences found on the retention of the homologues, when increasing the alkyl chain length, were more significant in the RP mode due to predominant hydrophobic interactions. A pH decrease and a salt concentration increase caused a retention decrease for both modes. A decrease on of the retention was observed when acetate anion was replaced by formate anion. The different order of the polynomial equations according to the used mobile phase confirmed its relevant role in the interactions with the analytes and stationary phase. A mobile phase was selected (85% acetonitrile, pH 4 and 100 mM ammonium formate) for the BAK determination in cutaneous, otic and ophthalmic formulations with different active pharmaceutical ingredients and excipients. Low sample volume (500 μL) and short analysis time (<5 min) were some of the advantages of the proposed method. In addition, good analytical performance (R² > 0.999, % RSD <4.5% for intra-day precision and <5.8% for inter-day precision, and recoveries in the 92-105% range) was obtained.

Mass transfer process and separation mechanism of four 5'-ribonucleotides on a strong acid cation exchange resin

5'-ribonucleotides including adenosine 5'-monophosphate (AMP), cytidine 5'-monophsphate (CMP), guanosine 5'-monophosphate (GMP) and uridine 5'-monophosphate (UMP) have been widely used in the food and pharmaceutical industries. This work focused on the assessment of mass transfer process and separation mechanism of four 5'-ribonucleotides and counter-ion Na⁺ on the strong cation exchange resin NH-1. The intraparticle diffusion was determined as the rate-limiting step for the mass transfer of AMP, CMP, GMP, and Na⁺ on the resin NH-1 through the Boyd model. Meanwhile, a homogeneous surface diffusion model (HSDM) combing ion exchange and physical adsorption was proposed and tested against adsorption kinetic data in the batch adsorption systems. The fixed-bed film-surface diffusion model based on the HSDM was then developed and successfully predicted the concentration profiles of 5'-ribonucleotides and the change of pH at the outlet of the fixed-bed in the dynamic adsorption and separation process. Finally, the separation mechanism of 5'-ribonucleotides was presented combining model prediction and experimental results. The separation of UMP, GMP and CMP were mainly based on their differences in isoelectric points, while that of AMP and CMP were lied with the discrepancy of their physical adsorption binding capacity with the resin NH-1.

Th4+ tuned aggregation-induced emission: A novel strategy for sequential ultrasensitive detection and separation of Th4+ and Hg2

A novel strategy, Th⁴⁺ tuned aggregation-induced emission, for sequential ultrasensitive detection and separation of Th⁴⁺ and Hg²⁺ was developed successfully. For demonstration this strategy, we designed and synthesized two tripodal gelators TH (tri-(isoniazid-4-yl)-functionalized trimesic acylhydrazine) and TA (tri-(pyridine-4-yl)-functionalized trimesic amide). The TH and TA could assemble into a stable supramolecular polymer hydrogel THTA-G in DMSO/H₂O (3.3:6.7, v/v) binary-solution. The THTA-G does not show aggregation-induced emission (AIE) effect. However, after addition of Th⁴⁺ into the THTA-G, the obtained metallogel THTA-GTh shows strong green AIE effect, which indicated that Th⁴⁺ could tune the gel generation of AIE effect. Interestingly, the THTA-G could ultrasensitive fluorescently detect Th⁴⁺, and the corresponding metallogel THTA-GTh could ultrasensitively detect Hg²⁺. The detection limits of THTA-G and THTA-GTh for Th⁴⁺ and Hg²⁺ are 8.61 × 10^-11 mol/L and 1.08 × 10^-11 mol/L, respectively. Additionally, the xerogels of THTA-G and THTA-GTh could separate Th⁴⁺ and Hg²⁺ from aqueous solution with excellent ingestion capacity, and the THTA-G could be used as a writable smart light-emitting material.