Electrolyzer-Powered Flame Ionization Detector

Abstract

We describe here a novel water electrolyzer-powered flame ionization detector (EFID), characterized by enhanced portability, reduced cost of operation and improved safety of operation and storage. A conventional FID operates with a hydrogen diffusion flame, which has a central flow of pure hydrogen and column effluents, surrounded by a much higher coaxial flow of pure air. In contrast, the EFID is based on the combustion of a premixed (unseparated), hydrogen and oxygen, stoichiometric gas mixture. This premixed gas mixture is provided by a simple water electrolyzer with low power and water consumption, without separation, compression, or pressure stabilization of the hydrogen and oxygen. The EFID is very similar to FID with two minor modifications: (a) The flame tip must have a narrow hole (∼250 μm) to prevent flame flashbacks. (b) The entire detector structure is maintained above 100 °C to prevent water condensation due to the lack of diluting air. The EFID sensitivity is similar to that of the FID, and up to twice improved detectivity is demonstrated with the EFID. The flame chemical ionization yield of the EFID linearly increases with the electrolysis current. The EFID response is linear over almost 6 orders of magnitude. The response is selective to carbon compounds where the response in aliphatic compounds is ∼30% lower than with aromatic compounds, and no observable difference for N-, S-, P-, and Cl-containing compounds. The use of splitless solvent injections with a megabore column (0.53 mm i.d.) quenches the flame. This flame extinction is eliminated by the use of a miniature air pump during the solvent elution time. Typical electrolyzer operating parameters are current of 1.5 A, 12 mL/day water consumption and 4 W electrolyzer power requirements. Thus, a relatively small size water electrolyzer can provide the total gas consumption of the EFID for up to 40 days before water replenishing is required. This EFID can also be operated either as an EFID or as an FID, simply by replacing the gas sources.