A rapid, sensitive method for the separation of catecholamine biomarkers (CAs), of importance in traumatic brain injury (TBI) and in Parkinson’s disease (PD), has been successfully developed using hydrophilic interaction liquid chromatography (HILIC). Dopamine (DA), epinephrine (EPI), and norepinephrine (NE) are known to be three to fivefold elevated above normal in traumatic brain injury (TBI) patients. HILIC facilitates the rapid and efficient separation of these polar biomarkers, which can be poorly retained by reversed-phase liquid chromatography (RPLC), while electrochemical detection (ECD) at the boron-doped diamond (BDD) electrode provides enhanced nanomolar detection. Three HILIC columns were compared, namely the superficially porous (core-shell) Z-HILIC column and the Z-cHILIC and Z-HILIC fully porous columns. The core-shell Z-HILIC showed the highest efficiency with a rapid separation within 60 s. The HILIC method utilizing the core-shell Z-HILIC column was initially optimized for the simultaneous analysis of DA, EPI, and NE using UV detection. The advantages of using the BDD electrode over UV detection were explored, and the improved limits of detection (LODs, S/N = 3) measured were 40, 50, and 50 nM for DA, EPI, and NE, respectively. Method validation is reported in terms of the linearity, repeatability, reproducibility, and LODs. Furthermore, the proposed method was successfully applied to the real sample analysis of urinary CAs following phenylboronic acid (PBA) solid phase extraction (SPE) pretreatment.

Benzalkonium chloride (BAK) is a mixture of alkyl benzyl dimethyl ammonium chlorides, which is used primarily as a biocide, surfactant, preservative, and antimicrobial agent in the pharmaceutical industry, in particular in ophthalmologic and nasal solutions. However, BAK may cause harmful consequences on the eye structures of the anterior segment. Control of BAK identity and content is necessary by applying a sensitive detection method. This study unravels the use of a glassy carbon (GC) electrode and a pristine boron‐doped diamond electrode (BDD) for the detection of four BAK homologs in a non‐aqueous medium using square wave voltammetry (SWV). The BDD provided more reproducibility of the oxidation potential than GC with a correlation coefficient of 0.999. The irreversible oxidation peak was very broad and deconvoluted into 3 peaks corresponding to C12, C14, and combined C16–C18 to reflect their concentration ratio in the mixture. The method was then extended to the detection of the C12 homolog in the ophthalmic formulations with a limit of detection (LOD) of 0.4 μg/mL. The estimated BAK levels in three  ophthalmic formulations were in agreement with the specified values by the manufacturers. The results were validated by high‐performance liquid chromatography (HPLC) with ultraviolet (UV) detection, confirming the presence of a single homolog (C12) in the eye drops.

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