Analytical apparatus and processes

Claim 1

Apparatus for the coulometric determination of a material present in successive samples which are introduced into the same batch of an electrolyte which is held in a coulometric cell, which cell comprises a generator electrode, which generator electrode generates a species which consumes the material and is located in the electrolyte, and a second electrode from which species generated do not reach the generator electrode, which apparatus comprises means to sense the presence of the material as a sensing signal and means to pass a sufficient quantity of electricity between the generator electrode and said second electrode to maintain or restore the sensing signal at or to its value when none of the material to be determined is present, said means to sense including a sensor electrode and a reference electrode, means to change the electrolyte in the coulometric cell in response to values of the sensing signal falling outside a predetermined limit, and control means for controlling said means to change including: (a) a differential to potential signal convertor having a high input impedance; (b) means for feeding (a) with a sensing signal which varies as the potential difference between the sensor and reference electrodes; (c) a differential potential input amplifier fed by (a) and by means for setting the output current of (c) to zero at a desired value of the sensing signal by feeding a suitable off-set potential to (c), the whole apparatus excluding the coulometric cell having a phase shift of less than 90° with the input signals received; (d) a comparator for comparing a potential signal produced by (a) with a pre-set potential; and (e) means in response to a signal from (d) indicating a potential signal from (a) in excess of that pre-set to operate means for changing the electrolyte in the coulometric cell.