Perhaps you should try some spelling variations:
"50 ppm decrease" » "50 _ decrease" (Expand Search), "50 a decrease" (Expand Search), "50 nn decrease" (Expand Search)
"5 ppm decrease" » "5 _ decrease" (Expand Search), "5 a decrease" (Expand Search), "5 nn decrease" (Expand Search)
"50 ng decrease" » "50 nn decrease" (Expand Search), "50 _ decrease" (Expand Search), "50 a decrease" (Expand Search), "50 mg decrease" (Expand Search), "5 ng decrease" (Expand Search), "50 ns decrease" (Expand Search)
"10 ng decrease" » "10 nn decrease" (Expand Search), "10 _ decrease" (Expand Search), "10 a decrease" (Expand Search), "100 ng decrease" (Expand Search), "10 mg decrease" (Expand Search), "10 nm decrease" (Expand Search)

You may be able to get more results by adjusting your search query.

• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"50 ppm decrease\") OR (((\"50 ng decrease\") OR (\"10 ng decrease\"))))) OR (\"5 ppm decrease\"))~".
• Removing quotes may allow a broader search: (((( 50 ppm decrease ) OR ((( 50 ng decrease ) OR ( 10 ng decrease ))))) OR ( 5 ppm decrease ))~.
• Adding a wildcard symbol may retrieve word variants: (((("50 ppm decrease") OR ((("50 ng decrease") OR ("10 ng decrease"))))) OR ("5 ppm decrease"))*.