The phrase "at two concentrations" is correct and usable in written English.
It can be used when discussing the presence or application of a substance or variable at two different levels or amounts.
Example: "The experiment was conducted at two concentrations to determine the effect on the reaction rate."
Alternatives: "at two levels" or "at two amounts".
Each one was tested at two concentrations, 1 and 25%.
In addition, CTP, GTP and UTP demonstrated similar increases at two concentrations of dFdC (Table 1).
NAC was administered prior to surgery at two concentrations (40 or 300 mg/kg, IP).
Liposomes were prepared using hydrogenated soy phosphatidylcholine (P90H, 60 mg/ml) and diclofenac sodium salt at two concentrations (5 10 mg/ml).
Using a custom-designed tubular flow cell, the metallic thin films were exposed to protein solutions of fibrinogen and albumin at two concentrations.
Experimental diets contained corn silage from a brown midrib (bm3) hybrid or its isogenic normal control at two concentrations of dietary NDF (29 and 38%).
Selectivity against PTH peptide fragments PTH 7-84) and PTH 3-84) were assessed by cross-reactivity and accurate spike-recovery to the QC samples at two concentrations.
Three material solutions were selected for study: maltodextrin DE5, whey protein isolate and gum arabic, each at two concentrations between 20 and 40 wt%.
The effectiveness of surfactants and MEs was evaluated at two concentrations from different sets of spontaneous imbibition tests and petrographic analyses.
The objective was to compare the effects of casein-, soy-, whey-, withoutthout glycomacropeptide (GMP -, alpha-lactalbumin-, gelatin-, or gelatin with tryptophan (TRP -protein breakfasTRP -proteinncentrations on subreakfastsatietwoand energy intake (EI).
Alder leaves were immersed in a stream of Northeast Portugal to allow microbial colonization before being exposed in microcosms of two types of SLNs at two concentrations for 42 days.
