So you should have:
Qt Code: 
  1. LIBS += -LD:/dev/CplusPlus/DemoFutronics -lftrScanAPI
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-L specifies a directory (among many) that should be searched by the linker for requested libraries
-l specifies the name of specific libraries that are requested to satisfy missing symbols in the program.

I have used the forward slash in the path to avoid the annoyance of escaping back slashes. Qmake does the right thing with these.