Spectrophotometric Determination of Iron(II) and Cobalt(II) by Direct, Derivative, and Simultaneous Methods Using 2-Hydroxy-1-Naphthaldehyde-p-Hydroxybenzoichydrazone

Table 5

Analytical characteristics of [Fe(II)-HNAHBH].

Parameter	Direct method	First derivative	Second derivative		Third derivative
	405 nm	427 nm	421 nm	435 nm	415 nm	426 nm
Beer’s law range (μg mL^−1)	0.055–1.373	0.027–1.376	0.027–1.376	0.027–1.376	0.027–1.376	0.027–1.376
Molar absorptivity, (L mol^−1 cm^−1)	5.6×10^4			—	—	—
Sandell’s sensitivity, (μg cm^−2)	0.0012			—	—	—
Angular coefficient (m)	0.974	0.072	0.006	0.093	0.002	0.085
Y-intercept (b)	0.0047	−0.0045	−0.1×10^−3	−0.1×10^−3	0.2×10^−4	0.9×10^−3
Correlation coefficient	0.9997	0.9999	0.9999	0.9999	0.9999	0.9999
RSD (%)	2.19	0.85	0.76	0.89	1.31	1
Detection limit (μg mL^−1)	0.065	0.1	0.022	0.0268	0.036	0.304
Determination limit, (μg mL^−1)	0.197	0.3	0.068	0.8	0.11	0.914
Composition (M : L)	2 : 3	—	—		—
Stability constant	1.8×10^18	—	—		—