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Table 8 Details with performance characteristics of reported visible spectrophotometric methods

From: Application of two charge transfer complex formation reactions for selective determination of metformin hydrochloride in pharmaceuticals and urine

Reagents and solvents used Methodology employed Linear range Molar absorption coefficient, L mol-1 cm-1 Remarks Reference No.
Iodine and acetonitrile The absorbance of yellow C-T complex of MFH with Iodine measured in acetonitrile at:
a) 360
b) 286
c) 230 nm.
1.656–72.86 mg mL-1 a) 1.03 × 104
b) 2.27 × 104
c) 3.63 × 104
Lower analytical wavelengths employed where photometric errors are possible. Incomplete validation reported [22]
Iodine and dichloroethane The absorbance of yellow C-T complex of MFH with Iodine measured in acetonitrile at 295 nm 2–12 μg mL-1 [24]
Copper(II) sulfate and cyclohexylamine Measurement of purple coloured product at 540 nm 0.5–2 mg ml−1 2.27 × 103 Less sensitive and larger volume of organic solvent required. [25]
Ninhydrin and alkali Measurement of MFH-ninhydrin complex at 570 nm 8–18 μg mL-1 57 Less sensitive and incompletely validated. [39]
Ninhydrin and ammonium molybdate mixture A C-T complex of MFH with ninhydrin formed at 90 C measured at 570 nm 10–30 μg mL-1 9.49 × 103 Not applicable for room temperature analysis. Incompletely validated. [40]
NaOCl, NaOH and ZnSO4 Measurement of yellow product The reaction is not suitable for routine metformin assay, since the amount of NaOCl required has to be comparable to that of MEB and an excess of NaOCl destroys the color development. Moreover the method was developed only for urine analysis. [41]
Triacetyl, 1-naphthol and alkaline ethandiol Measurement of colored products   Applicable to urine sample. Incomplete method validation. [42]
Bromothymol blue in phosphate buffer [43]
p-Chloranilic acid (PCA) and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and acetonitrile Measurement of C-T complex of MEB with:
a) p-CA at 530.0 nm;
b) DDQ at 460.0 nm
a) 8.0 to 320.0 μg mL-1
b) 1.6 to 64.0 μg mL-1
a) 0.733 × 103
b) 0.257 × 104
Methods have been completely validated. Applicable to analyse dosage forms and urine samples. Present work