Table 8 Details with performance characteristics of reported visible spectrophotometric methods

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