Use of Alizarin Red S as an Ion-Pair Reagent for the Spectrophotometric Assay of Fexofenadine in Pharmaceuticals and in Spiked Human Urine

Table 1

Comparison of the performance characteristics of the proposed methods with the existing visible spectrophotometric methods.

Sl. no.	Reagent/s used	Methodology	𝜆max; (nm)	Linear range; (μg/mL); (ε = L/mol/cm)	Remarks	Ref
1	(a) Chloramine-T-malachite green	Unrected chloramine-T measured	615	0.2–4	Exact concentration of CAT and dye to be known	[21]
	(b) Chloramine-T-Xylene cyanol FF		612	0.6–4
2	Bromothymol blue	Chloroform extractable ion-pair complex measured	412	10–50	Less sensitive, narrow linear dynamic range	[22]
3	Chromotrope 2R	Methylene chloride extractable ion-pair complex measured	512	30–120	Less sensitive, narrow linear dynamic range	[23]
4	(a) Bromothymol blue	Chloroform extractable 1 : 1 ion-pair complex was measured	409	0.5–9.0	Less sensitive	[24]
	(b) Bromophenol blue		411	1.0–6.0
	(c) Bromocresol green		414	1.0–8.0
	(d) Bromocresol purple		411	0.5–6.0
5	(a) Safranin-O	Chloroform extractable ion-pair complex was measured	520	10–50	Less sensitive	[25]
	(b) Methylene blue		650	10–50
6	Alizarin red S	Dichloromethane extractable ion-pair measured	440	0.4–12.0; (ε = 3.8 × 10^4)	Simple, highly sensitive and wide linear range, economical, and no standardization.	This Work
	FFH-AZS ion pair broken with ethanolic KOH	breaking of the yellow FFH -AZS ion-pair complex and measurement of violet-colored dianionic form of the dye in alkaline medium	590	0.2–3.5; (ε = 1.6 × 10^5)