A Y-shaped Teflon connector was designed to branch the capillary of a conventional commercial flame atomic absorption spectrometer for the introduction of inorganic Hg2+ aqueous solution and KBH4 solution. The two solutions were merged inside the connector before being nebulized into an aerosol by air in the nebulizer of the instrument, and the atomic absorption of mercury in the cold vapor and the aerosol was directly measured at ambient temperature without gas–liquid separation and without a flame. The limit of detection was 0.01 μg mL−1. The connector is easy to assemble and disassemble. It is a very simple and cost-effective way to exploit a conventional atomic absorption spectrometer for the determination of mercury. This method also features the use of a plentiful auxiliary gas (the ambient air only), simple reagents (KBH4 and NaOH only) and no need for flame or electricity for atomization.