That information I posted is actually provided by the manufacturers of nitrile gloves on their sites. I have heard of this before. Have you tried going to the manufacturer site and checking their section on "common questions asked by customers.?"
Analogous situation for people analyzing drinking water using IC: I just opened a new box of vials. When I do my drinking water analyses I have high levels of sodium, magnesium, and chloride. Are my vials contaminated...I want another lot...OK 3 lots later...still same problem...then after a bit of work..
Where do you eat lunch?
Do you eat fries?
Do you wear gloves when you pull the vials prep yur stds and samples and set up your runs?
Soure of contamination...(the interface/analyst)
(Let me also add that the enclosed instructions that came with the vials explaining they should be thoroughly rinsed prior to analysis were not being followed). Either they were not read or they were overlooked.
If there is a contamination issue (e.g. change in any aspect of result) where there was not one before always try to eliminate/rule out any step or part of the procedure that might involve human error...anything touched by the interface/analyst is/should be subject to inquiry. This suggestion is based purely on experience.
USGS and EPA requirements for cleaning sampling equipment or "clean hands" water quality and aquatic sampling call for non-powdered disposable gloves. Both organic and inorganic compounds sampling protocol allows for latex gloves while organic compounds also can use nitrile gloves and inorganic compounds can use vinyl gloves.
Check the website of the manufacturer of the gloves. Also, the EPA and USGS site may give you additional information.