Kinetic Spectrophotometric Determination of N-Acetyl-L-cysteine Based on a Coupled Redox-Complexation Reaction

Abstract

Surprisingly, to the authors' knowledge, there are only two published kinetic spectrophotometric methods for the determination of NAC. 15,16 Also, none of the cited methods for the determination of NAC has used Fe 3+ and 2,4,6-trypyridyl-s-triazine (TPTZ) as a reagent solution. In this report, a novel, simple and sensitive kinetic spectrophotometric method with TPTZ as the chromogenic reagent for the determination of NAC is described and validated. Ease of application, sensitivity, short analysis time, low cost and reliability are its main advantages. The initial rate and fixed-time methods, after their optimization and validation, are adopted for the determination of NAC in its pharmaceutical formulations. Experimental ReagentsAll chemicals were of analytical-reagent grade, and solutions were prepared in Milli-Q deionized water.A stock solution of NAC, 1.0 × 10 -2 mol L -1 , was prepared by dissolving 163.2 mg of NAC (Merck, Darmstadt, Germany) in deionized water up to 100.0 mL in volume. The stock solution was stable for at least 30 days when it was stored in a dark bottle at 4 C. Working solutions of lower concentration were prepared daily by appropriate dilution of the stock solution with deionized water.A stock solution of Fe 3+ , 1.0 × 10 -2 mol L -1 , was prepared by dissolving 270.3 mg of FeCl3·6H2O (Kemika, Zagreb, Croatia) in a portion of deionized water. Concentrated hydrochloric acid (0.5 mL) was added to prevent the hydrolysis of iron, before making up to a volume of 100.0 mL.A stock solution of TPTZ (Merck, Germany), 1.0 × 10 -2 mol L -1 , was prepared by dissolving 312.3 mg in 2.0 mL of HCl (c (HCl) = 6.0 mol L -1 ), and diluted to 100.0 mL with deionized water. A stock solution of TPTZ was stored in a dark bottle at 4 C. A novel simple kinetic spectrophotometric method for the determination of N-acetyl-L-cysteine (NAC) has been developed and validated. The proposed method is based on a coupled redox-complexation reaction, the first step of which is the reduction of Fe 3+ by NAC; the second one includes the complexation of Fe 2+ , resulting from the preceding redox reaction, with 2,4,6-trypyridyl-s-triazine (TPTZ). The stable Fe(TPTZ)2 2+ complex exhibits an absorption maximum at λ = 593 nm. The initial rate and fixed-time (at 5 min) methods were utilized for constructing calibration graphs. The graphs were linear in concentration ranges from 4.0 × 10 -6 to 1.0 × 10 -4 mol L -1 for the initial rate method and 1.0 × 10 -6 to 1.0 × 10 -4 mol L -1 for the fixed-time method, with detection limits of 1.0 × 10 -6 and 1.7 × 10 -7 mol L -1 , respectively. The proposed methods were successfully applied for the determination of NAC in its commercial pharmaceutical formulations.

Kinetic Spectrophotometric Determination of N-Acetyl-L-cysteine Ethyl Ester (NACET) Generating Chromogenic Copper(I)Ln Complexes with Different Ligands

“…Noteworthy, the same Fe(III)-ligand systems have been successfully used for the kinetic determination of NAC. [8,9] Under the optimum conditions previously reported for NAC we found considerable differences between NAC and NACET (Supplement materials Figure 1 and Figure 2). These results indicate the possibility of determining NAC in the presence of NACET.…”

“…In the literature, there have been reported many spetrophotometric methods for the determination of NAC. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] One group of described methods involves redox reactions with NAC in which a colored compound is formed or decomposed during determination. Among the described indirect spectrophotometric procedures one of the most common approaches to the determination of NAC is based on the coupled redox complexation reaction.…”

“…Among the described indirect spectrophotometric procedures one of the most common approaches to the determination of NAC is based on the coupled redox complexation reaction. The first step is the reduction of Fe(III) by NAC, followed by the determination of produced Fe(II) using various chromogenic reagents: 1,10-phenantroline, [4,8,12] hexacyanoferrate(III), [13] ferrozine, [6] 2,4,6-trypyridyl-striazine [9,18] and ferricyanide. [14] Cu(II)-neocuproine has also been used for the analysis of NAC of which the sulfhydryl group (SH) reduces Cu(II)-neocuproine to the chromogenic Cu(I)-neocuproine.…”

Kinetic Spectrophotometric Determination of N-acetyl-L-cysteine Based on the Reduction of Copper(II)-neocuproine Reagent

“…5,8,23,24,[28][29][30]35 There are few developed spectrophotometric methods based on the reduction of the Fe III to Fe II with NAC, followed by the complexation of Fe II with different reagents: 1,10-phenanthroline (phen), 5,23,28 ferrozine, 8 2,4,6-trypyridyl-s-triazine (TPTZ), 24,35 hexacyanoferrate(III) 29 and ferricyanide. 30 The authors have developed kinetic spectrophotometric methods for determination of NAC using Fe IIIphen reagent 23 The Cu(II)-neocuproine reagent is milder and therefore more selective oxidant than Fe III -phenantroline reagent.…”

“…The literature is still poor in analytical procedures based on kinetic spectrophotometry for the determination of the examined analyte. Beside two kinetic spectrophotometric methods for the determination of NAC developed by our team, 23,24 there are only two published kinetic spectrophotometric methods. 25,26 In this report a novel simple and sensitive kinetic spectrophotometric method with the chromogenic reagent, copper(II)-neocuproine for the determination of NAC is described and validated.…”