Patent GB-1524479-A (GB)
Title: Automatic process titration system
IPC: G01N27/44
Filed: 1976-09-14
Abstract: 1524479 Automatic titration system FOXBORO CO 14 Sept 1976 [17 Oct 1975] 37979/76 Heading G1N An automatic titration system with electrolytic generation of titrant has means for flushing a titration cell with fresh reagent (from which the titrant will be generated), means for generating titrant until the end point condition is reached in the reagent, means for introducing a sample and again generating titrant until the end point is reached and means for measuring the charge utilized in the second generation of titrant. The first generation of titrant sets the cell to a zero condition and obviates the need for accurate control of the fresh reagent. The system is further characterized by a fluid loop 50, round which the solutions are pumped during measurement and which comprises a sample valve and a reagent valve, each of which is a two position valve which, in one position defines the loop and a through flow of sample and in the other position supplies a predetermined volume of sample and reagent respectively to the loop. As shown, the titrator cell 12 comprises a generator electrode 20 separated from an auxiliary electrode 22 by a porous frit 18 and reference and indicating electrodes 30, 28 connected to an end point detector. The cell 12 also includes a magnetically driven impellor which normally drives liquid round flow-path 50. The indicating and reference electrodes 28, 30 are connected to an end point indicator which supplies a level detector, settable to the desired end point. The electrolytic current generator 24 is coupled with timer 40 for determining the integrated current and the apparatus is controlled by a sequencing state generator 42 or a microprocessor. The valves 46, 52 are solenoid operated and preferably comprise a two position ceramic slider 60 movably sandwiched between two housing blocks 62 biased against it. The sample valve 46 has two pairs of opposed inlets and outlets and three slider bores 76, the middle one of which moves from one inlet-outlet pair to the other and the reagent valve has three inlets and three outlets and the slider has one bore 78 and two edge milled passages 80, 82. In operation, the valves are initially as shown in Fig. 2A. Reagent from container 54 is passed via the reagent valve and sample valve to the titrator cell and flushes old reagent via the reagent valve and auxiliary electrode to line 58 which leads via the reagent valve to waste or storage. The reagent valve is then moved to its other position and the pump circulates reagent round loop 50 while the reagent is initially titrated to the end point valve. The sample valve is then operated and injects a sample of volume equal to one of passages 76 into the flow loop 50 while maintaining the flow and process loops. The titration is then performed. The end point detection may be by pH, ion selective or noble metal electrodes or may be amperometric or colourimetric. When a microprocessor controls the operation, the electrolysis current may be varied as the system approaches the end point in accordance with the results found during previous measurements.