Two palladium complexes, the [Pd(η2-ol)(8-(di-tert-butylphosphinooxy)quinoline)] and [Pd(η2-ol)(8-(di-tert-butylphosphinooxy)-2-methylquinoline)], have been used as sensing materials to functionalize quartz crystal microbalances (QCM). The developed sensors have been tested to determine carbon monoxide in air. The reversible binding of CO observed in CH2Cl2 solution for both complexes is retained in the solid state. The functionalized QCMs showed good reproducibility and sensitivity toward CO detection. While CO detection was not influenced by the presence of molecular hydrogen and methane, the humidity reduced the sensors sensitivity, although the functionalized QCMs were still able to discriminate CO.