'these concentrations' is correct and usable in written English.
You can use it as a noun phrase to refer to a specific group of things, such as "these concentrations of toxins in our water system."
The less water there is in the sea, the higher these concentrations will get.
Alfalfa is eaten by cows, not men, and Laug said these concentrations would not show up in milk and meat.
Even at these concentrations, we are facing enormous uncertainties.
Outside of these concentrations the population is sparsely distributed.
The geography of the global economy consists of both world-spanning networks and these concentrations of resources, as provided by about 40 global cities.
Democrats can rely on Los Angeles county and the San Francisco Bay area, but these concentrations are now surrounded by Republican territory.
These concentrations were 0.001-0.05 μg/ml.
These concentrations disrupted the cell membrane causing cytoplasmic leakage [137].
These concentrations depend upon the spatial coordinates and time.
These concentrations were prepared separately in each Erlenmeyer flask.
These concentrations ranged from 0 to 22 μg/g.
