The detailed study on the extraction capacity of N, N, N′, N′-tetraalkylderivatives of diglycolamide (DGA) was performed by using the novel analytical method, which determines the limit of metal concentration in the organic phase (LOC). The analytical results suggest that LOC of Nd(III) by N, N, N′, N′-tetraoctyl-diglycolamide (TODGA) depends on HNO 3 concentration and temperature. In order to increase LOC and suppress the third liquid phase, the modifier, N, N-dihexyl-octanamide (DHOA) of the aliphatic diluent was employed and its effect was investigated. The modifier can raise the LOC value, and it is noteworthy that LOC corresponds to the stoichiometric value, which is obtained by the extraction reaction, by using the extraction solvent of 0.1 M TODGA—(0.5–1 M) DHOA in n-dodecane. This condition suppresses the third liquid phase. In the absence of modifier, the relation of several DGA based compounds with LOC was investigated. It is confirmed that LOC using N, N, N′, N′-tetradodecyl-diglycolamide (TDdDGA), whose extractant has the longest alkyl chain in this work and forms hardly the third liquid phase, reaches to the stoichiometric value.