Evaluation of hydrophilic interaction chromatography versus reversed-phase chromatography for fast aqueous species distribution analysis of Nickel(II)-Histidine complex species.

Nickel (Ni) is a trace heavy metal of importance in biological and environmental systems, with well documented allergy and carcinogenic effects in humans. With Ni(II) as the dominant oxidation state, the elucidation of the coordination mechanisms and labile complex species responsible for its transportation, toxicity, allergy, and bioavailability is key to understanding its biological effects and location in living systems. Histidine (His) is an essential amino acid that contributes to protein structure and activity and in the coordination of Cu(II) and Ni(II) ions. The aqueous low molecular weight Ni(II)-Histidine complex consists primarily of two stepwise complex species Ni(II)(His)1 and Ni(II)(His)2 in the pH range of 4 to 12. Four chromatographic columns, including the superficially porous Poro-shell EC-C18, Halo RP-amide and Poro-shell bare silica-HILIC columns, alongside a Zic-cHILIC fully porous column, were evaluated for the fast separation of the individual Ni(II)-Histidine species. Of these the Zic-cHILIC exhibited high efficiency and selectivity to distinguish between the two stepwise species Ni(II)His1 and Ni(II)His2 as well as free Histidine, with a fast separation within 120 s at a flow rate of 1 ml/min. This HILIC method utilizing the Zic-cHILIC column was initially optimized for the simultaneous analysis of Ni(II)-His-species using UV detection with a mobile phase consisting of 70% ACN and sodium acetate buffer at wwpH 6. Furthermore, the aqueous metal complex species distribution analysis for the low molecular weight Ni(II)-histidine system was chromatographically determined at various metal-ligand ratios and as a function of pH. The identities of Ni(II)His1 and Ni(II)-His2 species were confirmed using HILIC electrospray ionization- mass spectrometry (HILIC-ESI-MS) at negative mode.

Rapid and sensitive simultaneous separation and electrochemical detection of tetracaine hydrochloride and oxymetazoline hydrochloride in pharmaceutical formulations via core-shell reversed-phase liquid chromatography.

Tetracaine hydrochloride (TCH) is a nasal anesthetic and oxymetazoline hydrochloride (OZH) is a nasal decongestant. A moderate to acute overdosage of OZH and TCH can lead to mydriasis, nausea, cyanosis, tachycardia, dyspnoea, cardiovascular failure, disorientation, seizures, and even death. Liquid chromatography (LC) has been mainly utilized for the individual determination of either TCH or OZH; however, there is a need for rapid and efficient methods for simultaneous analysis in pharmaceutical formulations and aqueous samples. This study highlights the use of the fast and efficient separation capabilities of core-shell silica particles in liquid chromatography (LC) for the simultaneous determination of TCH and OZH using UV detection and the enhanced selectivity afforded by electrochemical detection at a boron-doped diamond (BDD) electrode. Rapid reversed-phase (RP) separation and detection of OZH and TCH in nasal spray and eye drops was achieved within 45 s using a poroshell 120 EC-C18 column, by adjusting the ratio of organic solvent, mobile phase pH, detection potential and mobile phase flow rate. Sensitivity was compared using ultraviolet (UV) detection at 280 nm, and ECD at + 1.3 V with detection limits of 40 and 70 nM for TCH and OZH, respectively. The developed rapid method was utilized successfully in the analysis of pharmaceutical formulations, where the estimated levels of TCH and OZH in these formulations are in agreement with the specified values outlined by the manufacturers.