Solid phase microextraction and selective determination of cysteine in whole blood by cyclic voltammetry with silver nanoparticles modified clustered carbon fiber electrodes

Abstract

In the present paper, the solid phase microextraction of cysteine from aqueous solutions using a carbon fiber clustered electrode surface modified with silver nanoparticles was studied by cyclic voltammetry. The extraction dynamics and thermodynamics follow an exponential decay function and a Weibull function, respectively. Extracting cysteine onto the surface of the silver particles results in an improvement of the irreversible redox behavior of the silver particles with the cathodic peak shifted positively and the anodic peak shifted negatively, and this procedure can be used for the detection of cysteine in aqueous solution. Under the optimal experimental conditions including scan rate, solution pH and extraction time, the relationship between anodic peak current and the logarithm of cysteine concentration was linear in the concentration range of 1.0 × 10⁻¹³ to 1.0 × 10⁻² M with two regression equations of i_pa (μA) = 71.61 + 0.5221 log (c,M), (R = 0.9698, SD = 0.315) in the range of 1.0 × 10⁻¹³ to 1.0 × 10⁻⁸ M (LDM = 1.0 × 10⁻¹³ M) and i_pa = 72.84 + 9.612 log (c, M) (R = 0.9918, SD = 2.59) in the range of 1.0 × 10⁻⁸ to 1.0 × 10⁻² M (LDM = 1.0 × 10⁻⁸ M), respectively. The maximum tolerance was up to 100 : 1 molar ratios of cysteine to albumin protein, glycine and cystine, below which the interferents show little influence on the anodic peak current. The method was applied to the detection of cysteine in a mouse whole blood sample. The content of cysteine in the sample was measured as 36.5 (± 1.6) μM, which is in accordance with the values reported in the literature.