Electronic system for providing specificity in an electrochemical analytical device

An apparatus for providing specificity in an electrochemical analytical device and for continuous determination of a nitroglycerin concentration in a sample solution which comprises:

• a three element electrochemical cell having a grounded anode, a calomel reference electrode and a cathode electrode;
• modulator circuit means, electrically coupled to said electrochemical cell, for supplying a square wave modulated negative potential signal to said cathode electrode;
• demodulator circuit means, electrically coupled to said modulator means, for measuring the difference in the cell current of said electrochemical cell between said cathoe electrode and said anode electrode at the part and finish of said square wave modulated negative potential signal pulse and for generating an output signal proportional to said nitroglycerin concentration;
• gating circuit means, electrically connected to said modulator and demodulator means, for supplying a continuous pulse signal to said modulator means and for controlling said demodulator means to allow only the cell current generated by the reduction of said nitroglycerin concentration to pass through said gating means, and to allow substantially all switching current transients generated in said electrochemical cell to decay,
• inverter-amplifier means electrically coupled to said gating means for filtering and amplifying said cell current passed by said gating means;
• and
• indicator means electrically connected to said amplifier means for providing an output signal proportional to said nitroglycerin concentration in said sample solution.