A novel electrochemical analysis of the legal psychoactive drug caffeine using a zeolite/MWCNT modified carbon paste sensor

Abstract

Caffeine (Caf) is a natural central nervous system stimulant categorized by the US Food and Drug Administration as a safe drug and its maximal amount in soft drinks has been approximately determined to be lower than 200 mg L⁻¹. It is the world's most extensively used legal and unregulated psychoactive medication. A simple, low cost, sensitive and selective electrochemical method for the detection of Caf was developed using zeolite (Zeo) mixed with multi-walled carbon nanotube (MWCNTs) to give a modified carbon paste electrode (CPE) in a surfactant improved medium with sodium dodecyl sulfate (ZMWCNTMCPE/SDS) and carrying out cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV) measurements. Scanning electron microscopy (SEM) was also used to characterize the surface. The influence of varying the concentration versus the anodic current of Caf gives two linear ranges, the first is from 1.0 × 10⁻⁵ to 1.0 × 10⁻⁴ mol L⁻¹, with a correlation coefficient of 0.9878, and the second is from 1.0 × 10⁻⁴ to 5.0 × 10⁻⁴ mol L⁻¹. The limits of detection and quantitation were found to be 7.5 × 10⁻⁸ and 2.5 × 10⁻⁷ mol L⁻¹ respectively. The results show that the new sensor can be used to quantify Caf in black tea, coffee, Nescafé, Pepsi cola, diluted energetic drink samples, in real samples and Panadol extra pharmaceutical tablets. Satisfactory recoveries for all of the samples were obtained between 99.51% and 102.19% with relative standard deviations of 1.7–5.1%.