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

Table 11

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

Parameter	Direct method	Second derivative		Third derivative
	425 nm	431 nm	443 nm	437 nm	449 nm
Beer’s law range (μg mL^−1)	0.118–3.534	0.059–4.712	0.059–4.712	0.059–1.380	0.056–1.380
Molar absorptivity, (L mol^−1 cm^−1)	2.3×10^4	—	—	—	—
Sandell’s sensitivity, μg cm^−2	0.003	—	—	—	—
Angular coefficient (m)	0.375	0.0003	0.093	0.0002	0.009
Y-intercept (b)	0.0197	3.2×10^−5	−0.9×10^−4	−0.2×10^−4	−0.9×10^−4
Correlation coefficient	0.9999	0.999	0.9999	0.9999	0.9999
RSD (%)	1.37	1.84	4.3	1.15	7.6
Detection limit (μg mL^−1)	0.04	0.06	0.13	0.04	0.21
Determination limit, (μg mL^−1)	0.124	0.18	0.39	0.114	0.65
Composition (M : L)	2 : 3	—	—		—
Stability constant	7.7×10^19	—	—		—