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Publication: Dual self-ratiometric probe for smartphone-based microplate reader and colorimetric determination of L-Carnitine in pharmaceuticals
Together with the Department of Pharmaceutical Analytical Chemistry (Tanta University, Egypt) we published a new determination method of the non-protein amino acid L-Carnitine in Microchemical Journal.
L-Carnitine is a non-protein amino acid that is a critical substance involved in fat metabolism of all living organisms. Due to its simple structure, its direct determination is accomplished only by using sophisticated and expensive instruments e.g. LC-MS/MS and it can hardly be derivatized. In this work, a novel self-ratiometric derivatization-less colorimetric probe has been developed for determination of L-carnitine. The probe is based on the ability of L-carnitine’s quaternary amine to bind to ionized yellow form of bromophenol red at pH of 7.0 leading to equilibrium shift and an increase in dye’s pka and dye color was changed back from violet to yellow. This was accompanied by a marked decrease in absorbance at 580 nm along with a slight increase at 440 nm. Thus, a colorimetric probe was constructed based on measuring A580/A440 as a function of L-carnitine concentration showing excellent linearity between 20 – 140 µg/mL with a LOD of 6.9 µg/mL. The smartphone-based microplate reader method relied upon recording the ratio of magenta and yellow color components of CMYK color model with excellent linearity between 50-180 µg/mL. The probe demonstrated acceptable accuracy (% recovery within 100±2 %), precision (% RSD < 2 %), and selectivity. The devolved ratio colorimetric probe was successfully applied for L-carnitine determination in its capsules and simulated intestinal fluid. The probe showed an excellent profile regarding both eco-friendliness and practicality so that it be adopted for its routine analysis in quality control or research labs.
A.A. Abdella, R. Ulber; Dual self-ratiometric probe for smartphone-based microplate reader and colorimetric determination of L-Carnitine in pharmaceuticals; Microchemical Journal (2025) in press