基本信息
摘要：1,151,501. Determining the molar concentration of solutions, electrically. PERKINELMER Ltd. July 6, 1966 [April 6, 1965], No.14609/65. Heading G1N. The molar concentration or molecular weight of a solution is monitored by observing the change in resistance of a semi-conductor bead thermistor 39 as the solution flows from an outlet 37 of a tube 27 over the bead surface in the form of a film, which solution may be effluent from a chromatograph column (not shown). The bead resistance may be compared in a bridge with a fixed reference resistance, or alternatively with the resistance of a reference bead 41 over which a carrier liquid or solvent, as used in the column, flows in the form of a film from an outlet 38 of a tube 28. The vertical separation of the respective outlets and beads is adjustable to produce the films. The thermistor sensors are contained in an isopiestic chamber 19 (i.e. a chamber containing a constant vapour pressure of solvent) on the base of which is a pool 50 of solvent similar to that used as the carrier in the column. Over-flow funnels 40, 44 prevent contamination of the pool by the effluent. The inner surface 17 of the chamber is lined with absorbent material to assist evaporation of the solvent. Operation The chamber is within a thermally insulating casing 1, 2 which is temperature controlled and in operation is heated by an electric heater 7, air being circulated by a fan 10, until steady state temperature conditions are reached and the pressure of evaporated solvent remains constant which in general is when the chamber is saturated with solvent. The resistance of the beads will then be stable. The flow of the effluent solution and solvent over the thermistors is then commenced. Since the effluent comprises the solvent and traces of a sample under analysis it will have a lower vapour pressure than the solvent, dependent on the quantity and molecular weight of the sample constituents; which results in condensation of solvent vapour on the effluent surface whose temperature then increases. This increase is detected by the bead 39 and upsets the balance of a constant voltage input D.C. bridge. Equilibrium is reached when the vapour pressures of the effluent and solvent become equal, and the temperature difference which then exists indicates the molar concentration of the sample constituents on the bead 39 at that time. By adjusting the bridge until balanced a record of temp. difference is obtained or alternatively the bridge output may be connected to a chart recorder. The refractive index of the effluent may also be detected, and is dependent on density, also the molecular weights at various peaks can be derived by correlation of the reading of total mass and total number of moles. The arrangement may be used to compare two liquids.
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