Fast Ultrasensitive Sensing Strip for the Electrochemical Determination of Vitamin B6

Vitamin B6 is a coenzyme involved in more than 150 biochemical reactions in the body. Its intake has favorable effects for many diseases like Parkinson's disease, glaucoma, and endometriosis. Vitamin B6 can be obtained from tablets, aqua vitamin, and a variety of food sources, including meat, fish, and vegetables. There is a need for process analytical control for fast, ultrasensitive, and selective methods of determination of vitamin B6 in order to produce drugs of high pharmaceutical purity. Also, the on-site determination of vitamin B6 in vegetables can contribute to the fast, real-time control of the quality of vegetables. Therefore, a fast ultrasensitive sensing strip based on the immobilization of heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin on a matrix containing single-walled carbon nanotubes was constructed and used for on-site pharmaceutical process control of vitamin B6, as well as for on-site quality control of food. The sensing strip provided two linear concentration ranges: the first one between 1.69 × 10^-15 and 1.69 × 10^-5 g mL^-1 with a sensitivity of 6.96 × 10⁴ s^-1 g^-1 mL, and the second one between 1.69 × 10^-5 and 1.69 × 10^-3 g mL^-1 with a sensitivity of 3.65 × 10² s^-1 g^-1 mL. The limit of quantification was 1.69 fg mL^-1. A % recovery higher than 94.50% was determined for Vitamin B6 in tablets, aqua vitamin, and avocado, with % relative standard deviations lower than 1.00%. A lower determination limit was obtained when the sensing strip was used for the assay of vitamin B6 in different samples compared with other methods used to date for its assay. Also, the results of the analysis were obtained faster, in real time, compared with other methods for which a long sample processing time is needed before analysis.