|
| Sl. No. | Reagent/s used | Methodology | Linear range (g mL−1) and molar absorptivity (l mol−1 cm−1) | Remarks | Reference |
|
| (1) | Chloramine-T and metol | Red-colored product was measured at 520 nm | 0.0–40
() | Less sensitive, metol solution is not stable, and even the blank absorbance is high | [15] |
| (2) | Potassium iodate
(1) Dichlorofluorescein
(2) Carbontetrachloride | The absorbance of the red-colored solutions was measured at 520 nm | (1) 2.5–25
()
(2) 200–1400
() | Require strict pH control, and the sensitivity of the method which involves extraction was very less | [16] |
| (3) | (a) Bromocresol green
(b) Bromothymol blue | Ion-pair complex measured at 420 nm | 2.0–23
()
0.7–8.1
) | Sensitive but required close pH control and extraction use of organic solvent | [17] |
| (4) | (a) Chloranil
(b) DDQ
(c) DCNP | The increase in the absorbance is measured at 458, 460, and 425 nm, respectively | 50–500 | Poor sensitivity and use of organic solvent | [18] |
| (5) | Tetracyanoquinodimethane | Green radical anion measured at 840 nm | 1.0–7.0 | Uses expensive reagents and organic solvents | [19] |
| (6) | (a) P-chloranilic acid in methanol
(b) P-chloranilic acid in acetonitrile | C-T complex measured at 525 nm | (a) 16000–110000
(b) 25–240 | Less sensitive, uses acetonitrile which is very expensive | [20, 21] |
| (7) | Copper (II) chloride in methanolic medium | Blue-colored complex measured at 660 nm | 200–1200
() | Less sensitive, narrow linear range, and use of organic solvent | [22] |
| (8) | Cupric acetate | Complex measured at 630 nm | 50–1250 | Poor sensitivity | [23] |
| (9) | Palladium (II) | Yellow-colored complex measured at 345 nm in the pH range 2.23–8.50 | 17–200 | Sensitive but required close pH control | [24] |
| (10) | Ninhydrin in methanolic medium | Blue-colored product measured at 590 nm. | 5.0–30.0 | Requires heating in a boiling water bath and use of organic solvent | [25] |
| (11) | Sodium nitroprusside | Orange species formed in alkaline medium measured at 498 nm | 50–500 | Poor sensitivity | [26] |
| (12) | Brominating mixture | Yellow-colored developed measured at 350 nm | 40–200 | Less sensitive and measured at shorter wavelength | [27] |
| (13) | F-C reagent | Blue-colored product measured at 650 nm | 16–48 | Less selective | [28] |
| (14) | Fe (III) with
(a) 1,10-phenanthroline
(b) 2, 2-bipyridyl | (a) Ferroin measured at 510 nm (b) Fe (II)-bipyridyl complex measured at 520 nm | (a) 2–12
()
(b) 8–16
) | Requires heating and longer reaction time | [29] |
| (15) | NBS with p-aminophenol | The decrease in the absorption intensity of the colored product measured at 552 nm | 6.0–22.0 | Two-step reaction, longer reaction time, and narrow linear range | [30] |
| (16) | NBS
(a) indigo carmine
(b) neutral red | Resulting colored products peaking at 610 nm and 530 nm | 0.8–6.0
()
0.3–3.0
() | Highly sensitive, no heating or extraction step, inexpensive instrumental setup, use of ecofriendly chemicals, and aqueous system | Present methods |
|
