Octreotide (OCT), a synthetic octapeptide analogue of nature somatostatin hormone has been extensively used in cancer treatment and growth hormone related diseases. Herein, a first efficient voltammetrical approach is presented for determination of OCT based on its strong hydrophobic interaction with the untreated carbon paste electrode (CPE) surface. The electrode reaction mechanism of OCT was proposed for the first time based on the presence of well-shaped irreversible and adsorption-driven oxidation peak of its Tryptophan amino acid moiety. The adsorption data is fitted well to Freundlich isotherm model indicating favorable and a physical multilayer adsorption process. Further, LS-AdASV and SW-AdASV methodologies involve the selection of optimal conditions for OCT oxidation at CPE, analytical performance and interference study. The usefulness of our elaborated electroanalytical protocol was verified in the simple, sensitive and fast analysis of OCT in human plasma and its commercial formulation "Sandostatin injection". It also rendered low detection limit (LOD) of 7.66 × 10 −10 M in human plasma sufficient for clinical applications using SW-AdASV method. This direct electrochemical analysis of OCT molecule opens up new prospects for the detection of other peptides, hormones or proteins in biological samples and for development of various electrochemical sensor and biosensor devices for medicine and biochemistry.
An economical graphene-carbon paste electrode (GR/CPE) in situ modified with surfactants was used for improvement the sensitivity and selectivity of the electrochemical measurement of itraconazole drug. Among the surfactants, cationic (cetyltrimethyl ammonium bromide, CTAB) and non-ionic (Triton X-100) displayed a decrease in peak current intensity, while anionic (sodium dodecyl sulfate, SDS) exhibited better change in the electrical properties of the electrode-solution interface. The adsorbed-SDS at GR/CPE interacts with itraconazole molecules through hydrophobic and electrostatic attraction which encourages the electron transmission between the drug and electrode surface. Compared with CPE and GR/CPE, SDS-GR/CPE exhibits the enhanced peak current intensity and reduces the over potential toward itraconazole oxidation as a result of the combined effect of GR and SDS. % composition of GR/CPE and SDS concentration were optimized. Wide linear dependence of the current on bulk itraconazole concentration (1.5 × 10 −9 -7.0 × 10 −7 M) was achieved in Britton-Robinson buffer, pH 2.0 containing 0.5 mM SDS at 0.3%(w/w) GR/CPE. SDS-GR/CPE presents adequately LOD value (1.36 × 10 −9 ± 1.07 × 10 −10 M) for the determination of itraconazole in human plasma. SDS-GR/CPE avoids interference from important common substances in biological and pharmaceutical samples. The fabricated sensor has desirable stability and reproducibility that can be used in routine quality control and pharmacokinetic studies.
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