Nature's touch in the laboratory: eco-friendly and green dual-mode UV-vis and smartphone RGB analysis of procaine in pharmaceuticals using a non-heated aqueous matcha green tea extract

Using the principles of green chemistry, a new, simple, rapid, and eco-friendly dual-mode system for procaine detection in pharmaceutical samples was developed in this study. This system relied on the diazotization of procaine, followed by a coupling reaction with catechin-rich molecules present in a non-heated matcha green tea extract (MTE) in an acidic medium containing nitrite. As the concentration of procaine increased, the resulting yellow azo dye became visually more intense, which could be monitored using UV-vis spectrophotometry (<i>λ</i> = 412 nm) and smartphone-assisted RGB analysis (only <i>B</i> values varied; <i>R</i> and <i>G</i> values were constant). The spectrophotometric method allowed the detection of procaine as low as 0.33 mg L^-1, with a working concentration range between 1.0 and 8.0 mg L^-1. Alternatively, the smartphone-assisted method exhibited linearity over the 2.0-10.0 mg L^-1 range, with a minimum detectable concentration of 0.67 mg L^-1. The performance of the dual-mode system was confirmed by quantifying a real procaine sample, with the testing results showing good agreement with the results obtained using the reference spectrophotometric method. The influences of common ions were investigated, and Na₂EDTA was found to offer an easy method for eliminating Fe³⁺ interference. The total phenolic content of MTE was quantitatively determined using a Folin-Ciocalteu procedure to standardize the MTE.