Stewart spent 22 years with Hewlett Packard and Agilent Technologies supporting instruments for chemical analysis: GC, GCMS, LC, LCMS, UV/VIS, and lab data systems.

In 2001 Stewart moved to Isotechnika to support their drug discovery and development activities. Ultimately this also involved supporting building HVAC systems as well as instruments involved in clinical diagnosis of h. Pylori.
Currently in semi-retirement, he continues to support the analytical chemistry community with training, troubleshooting and incorporating new instruments into current laboratory workflow, His particular area of expertise being GCMS and LCMS. He operates a small isotope ratio reference lab in order to support the h. Plyori Urea Breath Test community with parts, repairs, consulting, and custom 13CO2/12CO2 isotope gas reference blends.