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Development of Flow Injection and Sequential Injection Methods for the Determination of N-Acetyl-L-Cysteine Ethyl Ester (NACET) Generating Chromogenic Copper(I)Ln Complexes With Different Ligands

New simple, sensitive and robust flow injection and sequential injection methods for the determination of a novel lipophilic thiol compound, N-acetyl-L-cysteine ethyl ester (NACET), have been developed, validated and compared. NACET is the ethyl ester of NAC, it has advantageous pharmacokinetics and is a potential drug and antioxidant. The proposed methods are based on the reduction of Cu(II)-ligand complex to Cu(I)-ligand complex with the analyte. Studied ligands were neocuproine, bicinchoninic acid (BCA) and bathocuproine disulfonic acid (BCS). The flow injection system consisted of an Ismatec IPC eight-channel peristaltic pump, Rheodyne low pressure Teflon six port rotary valve and three-line manifold with one reaction coil. For the sequential injection measurements Cheminert® M50 pump (VICI Valco), a syringe-free stepper motor driven pump, was used for liquid handling. A 10-port selection valve model C25-3180D with a multiposition actuator control module EMHCA-CE (VICI Valco) was used in conjunction with the M series pump. The signal was continuously monitored at 458, 562 and 483 nm for the reactions of NACET with neocuproine, BCA and BCS, respectively, using a Shimadzu UV-1601, UV/Vis spectrophotometer equipped with a flow through cell. Optimization of manifold parameters and experimental conditions were carried out by means of univariate method. Developed flow injection methods based on the reaction systems with neocuproine, BCA and BSC were linear in the concentration ranges:4.0 × 10−6 - 2.0 × 10−4, 2.0 × 10−6 - 1.0 × 10−4 and 6.0 × 10−7 - 1.2 × 10−4, respectively. The linear ranges of sequential injection methods were: 2.0 × 10−6 - 2.0 × 10−4, 2.0 × 10−6 - 1.0 × 10−4 and 2.0 × 10−6 - 1.2 × 10−4, respectively. The analytical performance of the methods, in terms of accuracy and precision, was established. The analytical frequency was 70 samples per hour for all proposed methods.

N-acetyl-L-cysteine ethyl ester, flow injection methods, sequential injection methods

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