The first question again is when you say "prep samples", does this ever mean salable/distributable product? If it does then you're on the same level as your manufacturing facility as stated above. If materials from the lab are never sold or introduced to your plant, and are used solely for experimentation, you really have no standard you have to meet other than to keep your employees and testers of these samples safe, and you have no "requirements".
If you wanted to follow my advice and stick to the FDA food code for your R&D lab to make sure that your samples are held to the same standard as a retail store, non-food grade substances would be defined as "Poisonous or toxic materials" in FDA food code, and your responsibilities would be:
See section 7-2 of the 2013 FDA food code: http://www.fda.gov/d...e/UCM374510.pdf
Only those POISONOUS OR TOXIC MATERIALS that are required for the operation and maintenance of a FOOD ESTABLISHMENT, such as for the cleaning and SANITIZING of EQUIPMENT and UTENSILS and the control of insects and rodents, shall be allowed in a FOOD ESTABLISHMENT
If you are preparing cosmetics or "items not intended to be ingested", then you aren't holding the area to the standard of a "food establishment", and instead as a multi-purpose room. The requirements for separation and product safety are only as strict as your intended scope of distribution of these samples. If it's in house only, do whatever you want as long as your employees are kept safe by your separation procedures . If it leaves the building, I would not recommend combining those functions any more than I would combine a pathogen testing lab with a sensory lab, or use my mixing bowls at home to mix fertilizer or epoxy.
A true laboratory by most standards doesn't permit eating to keep employees safe (OSHA, etc.), a "Test Kitchen" should really be that, a kitchen intended for preparing products that are safe to eat. Doing both in the same area is not best practice, so do what you can to eliminate risk and know that it's a potential point of improvement in your facility.