Table 4: Tolerance limits of some cations in derivative methods.

Foreign ionTolerance limit (in folds)
Direct methodFirst derivativeSecond derivativeThird derivative

Ag(I)14183522
Hg(II)11204030
U(VI)11122518
Mn(II)7201620
Th(IV)5101620
In(III)7284834
Au(III)4355528
Sn(II)<181522
Co(II)<1interfere715
Ni(II)<1interfere510
Cu(II)<151210