A circuit for setting a reference voltage in a floating gate circuit is configured as a precise voltage comparator circuit with a built-in programmable voltage reference. An illustrated example firearm includes a housing; a removable barrel; a latch to releasably secure the barrel in the housing, the latch having a released state and a secured state; and a carrying handle movable between a rest position and a carry position. The lower convex lens surface has a light exit surface, at the bottom, which faces the photodiode. A raffinate from the liquid-liquid extractor is passed to a distillation column.