NOVELTY - A hydrogen purity monitor (10) comprises: first fuel cell (11) configured to generate electrical current from the electrochemical reaction of hydrogen and oxidant, having a first fuel inlet; second fuel cell (12) configured to generate electrical current from the electrochemical reaction of hydrogen and oxidant, having a second fuel inlet; control system (20) configured to apply an electrical load to each fuel cell and determine an electrical output of each fuel cell; and a purity monitor output.    USE - As a hydrogen purity monitor, useful for monitoring hydrogen purity (claimed); and as a periodic testing system or as an in-line, continuously-operating fuel monitor.    ADVANTAGE - The hydrogen purity monitor is relatively inexpensive compared to existing elemental analysis apparatus. The system specifically detects or monitors contamination in order to assess fuel purity before it is delivered to customers.    DETAILED DESCRIPTION - A hydrogen purity monitor (10) comprises: first fuel cell (11) configured to generate electrical current from the electrochemical reaction of hydrogen and oxidant, having a first fuel inlet configured to receive hydrogen from a first hydrogen source; second fuel cell (12) configured to generate electrical current from the electrochemical reaction of hydrogen and oxidant, having a second fuel inlet configured to receive hydrogen from a second hydrogen source; control system (20) configured to apply an electrical load to each fuel cell and determine an electrical output of each fuel cell, where the control system includes comparator for comparing the electrical outputs of the first and second fuel cells; and a purity monitor output configured to give an indication of hydrogen purity based on an output of the comparator. An INDEPENDENT CLAIM is included for monitoring hydrogen purity involving supplying hydrogen fuel from a first hydrogen source to a first fuel cell configured to generate electrical current from the electrochemical reaction of hydrogen and oxidant; supplying hydrogen fuel from a second hydrogen source to a second fuel cell configured to generate electrical current from the electrochemical reaction of hydrogen and oxidant; applying an electrical load to each fuel cell and determining an electrical output of each fuel cell; comparing the electrical outputs of the first and second fuel cells; and providing an indication of hydrogen purity of one of the first and second hydrogen sources based on an output of the comparator.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic diagram of a fuel cell based hydrogen quality monitor.    Hydrogen source (5)    Hydrogen purity monitor (10)    First fuel cell (11)    Second fuel cell (12)    Fuel inlet (14)    Control system (20)