The phrase "a known quantity of" is correct and usable in written English.
It can be used when referring to a specific amount or measure of something that is recognized or established.
Example: "In the experiment, we used a known quantity of the chemical to ensure accurate results."
Alternatives: "a specified amount of" or "a defined quantity of".
The response (measured as rate of growth) to the unknown amounts of vitamin is compared with that obtained from a known quantity of the pure vitamin.
The procedure involves adding to a substance a known quantity of a radioisotope of the element to be measured and mixing it with the stable isotope of the element.
This allows calculation of the amount of radium in the solution, if the ionisation chamber has been standardised by a similar operation made with a known quantity of radium.
The bomb is placed in a known quantity of water.
Spray deposits were washed off the tracer plates with a known quantity of water.
Then, we simultaneously injected a known quantity of KMnO4 and FeCl2, respectively, into two separate compartments forming the upstream reservoir.
Ni-P-Ag composite coating was achieved through direct electrolysis by adding a known quantity of the conventionally prepared SNS into Ni-P bath.
After pH adjustments, a known quantity of dried biosorbent was added and the arsenic-bearing suspensions were kept under magnetic stirring until the equilibrium conditions were reached.
After pH adjustment, a known quantity of biosorbent (BREC) was added and the CR bearing suspensions was kept under magnetic stirring until the equilibrium was reached.
Thermo-gravimetric analysis (TGA) is a technique used to determine changes in weight of a known quantity of sample in relation to a change in temperature.
The reactor was filled with a known quantity of one reactant and the system was allowed to reach a steady-state temperature.
