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| SL number | Reagent/s | Methodology | Linear range (µg/mL) | Remark | Ref. |
|
| 1 | DCNQ | Orange coloured product in ethanol measured at 440 nm | — | — | [9] |
| 2 | DCNQ | Red coloured product formed in the presence of ammonia in alcoholic medium measured at 540 nm | 6–42 | 20 min contact time | [10] |
| 3 | Iron (III) | Purple-violet colour complex in acid medium measured at 510 nm | 0–36 | Less sensitive and the molar absorptivity is equal to 2.48 × 103 L/(mol⋅cm) | [11] |
| 4 | Iron (III) PPD | Thionine compound measured at 600 nm | — | Multiple step reaction involved | [12] |
| 5 | Sodium nitroprusside | Orange coloured product in basic medium measured at 510 nm | — | — | [13] |
| 6 | Sodium nitroprusside | Orange-red complex measured at 490 nm | 5–32 | — | [14] |
| 7 | PAR-V+5 | Ternary complex (1 : 1 : 1) extracted into chloroform and measured at 560 nm | 0.2–20 | 30 min contact time, extraction step is required | [15] |
| 8 | Osmic acid | Light yellow coloured product formed at pH4 measured at 375 nm | 0.25–40 | 60 min contact time, pH adjustment is required | [16] |
| 9 | NBS-CB | Unbleached dye colour measured in acid medium at 540 nm | 0.2–5.0 | Critical acid conc.; less stable reagent used | [17] |
| 10 | KMnO4 | Blue coloured manganate in alkaline medium measured at 610 nm (direct method) | 1–10 | Critical NaOH conc.
Reaction rate precariously dependent on experimental variables | [18] |
| Absorbance at a fixed time of 20 min measured (kinetic method) | 1–10 |
| 11 | Sodium azide-iodine | Decrease in absorbance at the 5th min measured at 348 nm (kinetic method) | 10–100 | Reaction rate precariously dependent on experimental conditions | [19] |
| 12 | Ce(IV)/ODS | Orange-red coloured species measured at 470 nm | 0.5–5.0 | Nondrastic experimental conditions, no critical pH adjust, no heating or extraction step. Shorter contact time (15 min), no use of organic solvent | Present work |
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