A capillary liquid chromatography method for benzalkonium chloride determination as a component or contaminant in mixtures of biocides

A method for quantifying benzalkonium chloride (BAK), an alkyl dimethyl benzyl ammonium compound, in several biocides formulations is proposed. A tertiary amine like N-(3-aminopropyl)-N-dodecyl-1,3-propanediamine (TA) and a straight-chain alkyl ammonium compound like trimethyl-tetradecyl ammonium chloride (TMTDAC), have been employed as trade surfactants besides BAK. Two capillary analytical columns with different polarities are tested: inertsil CN-3 capillary column (150 mm × 0.5 mm i.d., 3 μm particle diameter) and a non endcapped Zorbax C18 capillary column (35 mm × 0.5 mm i.d., 5 μm particle diameter). This latter column provided the best separation of the BAK homologues in less than 12 min using acetonitrile:acetate buffer (50 mM, pH 5) 85:15 at 20 μL min−1. The proposed method combines on-line in-tube solid-phase microextraction (IT-SPME) coupled to capillary liquid chromatography (CapLC) and UV diode array detection. Matrix effect was present when TA were in excess to BAK. If TMTDAC is the co-biocide, matrix effect is always present. A decreasing of analytical response mainly for C12-BAK homologue was found using both chromatographic columns. The charged amount of mixture in the system was the most important parameter for obtaining reliable results. 1 mL was the on line processed sample volume optimum for concentrations lower than 35 μg mL−1 of total surfactants. LODs were 0.03 μg mL−1 and 0.006 μg mL−1 for C12-BAK and C14-BAK, respectively. This method is also of use to evaluate the unwanted presence of BAK in biocide formulations due to industrial processes.