The flame ionization detector (FID) is the most widely used detector for gas chromatography (GC) and is also used as a stand-alone monitor of the total hydrocarbon concentration in air. Although very effective, the FID typically consumes 30 ml/min of hydrogen, 30 ml/min of helium make-up gas and 300-400 ml/min of pure air. Clearly, it is highly desirable to eliminate these gases, their cylinders, pneumatics and safety hazards from the FID and GC. Recently, a new type of FID was developed, based on the provision of a low flow rate of an unseparated gas mixture of oxygen and hydrogen, provided by a simple water electrolyzer. This electrolyzer-powered FID (EFID) considerably simplifies the gas logistics of GC-FID, improves its operational safety, reduces the cost of analysis and significantly improves its transportability. The water electrolyzer of the EFID contains a special chamber or canister, filled with either silica gel or molecular sieve particles, that serves for the adsorption of the water vapor. These powders or particles have a limited water capacity and need periodic manual replacement that may also result in leaks if some powder dust finds its way to the o-ring seal. Furthermore, the standard water electrolyzers are hard to automate and thus suffer from limited continuous operation time that is undesirable in a modern laboratory environment. The major reason for this situation is that while water is an easily transferable liquid, the needed solid water adsorbing material requires manual replacement periodically before its saturation and thus precludes the full automation of the EFID.
In a standard water electrolyzer, the oxygen and hydrogen gas mixture are formed as several thousand small bubbles per second and thus are saturated with water vapor and carry a large amount of water mist. This water mist is very harmful to the long-term operational stability of the electrolyzer, as the potassium hydroxide in the water tends to clog the gas flow path when the water evaporates. In addition, excessive loss of potassium hydroxide may require its undesirable periodic replenishment. Furthermore, when the water vapor itself condenses on the gas tube, it temporarily clogs the gas tube and can induce severe FID background noise and even result in total flame extinguishing. The water electrolyzer of the present invention is based on the elimination of the water mist and the reduction of the relative humidity to well below 100%, preferably to around 50%, in order to eliminate and solve the above-described problems.
The process of water mist elimination and humidity reduction can be achieved in several ways, including:
a) Two cells can be used, with a standard water-adsorbing material, a heating unit for each cell, and an air pump that can be directed to each cell. When a given cell is close to saturation with water, the electrolyzer gases can be directed through the second cell and the saturated cell is heated while room air is pumped through it to desorb the previously adsorbed water from it. Afterwards, it is closed, cooled back to room temperature and is ready for future service. The water adsorbing material also adsorbs the potassium hydroxide contained in the water mist. The need for two cells is only to enable full automation and relatively uninterrupted EFID operation. This arrangement is useful but somewhat complex, increasing the cost of the water electrolyzer and requiring some periodic addition of potassium hydroxide. PA1 b) A freon or hydrocarbon-based, small refrigerator can be built with a miniature closed refrigeration cycle unit for water mist and vapor recirculation. This is a possible approach, but may be too costly; it also suffers from reduced reliability. PA1 c) A miniaturized refrigeration unit, based on a Peltier semiconductor solid state device, can be built for water mist elimination and vapor pressure reduction. This unit seems to offer the ideal solution for the water mist and vapor management requirements. The basic idea is that the Peltier element will cool a gas condenser element located above the electrolyzer, so that the water mist and vapor will condense, liquefy and recirculate back to the water reservoir below. In this way, a mist-free gas mixture, with a relative humidity of about 50%, will be generated if the cooled condenser temperature is 10.degree. C. below room temperature. Therefore, the water electrolyzer of the present invention was built around a Peltier-based water mist and vapor recirculating and management system.