Author(s) :

Fabrice Maphasi Bakulu, Nicodème Kalenda Tshilombo, Jean Nsangu Mpasi, Adelard Mbenza Phuati, Elvis Baguma Iragi.

Volume/Issue :

Abstract :

Hydroquinone and kojic acid are widely used in skin-lightening products. For the regulatory interpretation in the DRC, maximum limits of 2% for hydroquinone and 1% for kojic acid were applied according to Ministerial Order No. 1250/CAB/MIN/SP/008/CJ/MP/2013. To validate an HPLC-UV method for quality control over the 5–80 μg/mL range and assess compliance of products manufactured in Kinshasa with the applied specifications of 2% hydroquinone and 1% kojic acid.This cross-sectional analytical study used non-probability purposive sampling of 14 locally manufactured products labelled as “lightening” or “clarifying” and collected in December 2025 in the Mont-Amba district. Validation was performed in lotion, cream, and body-milk matrices at 5, 10, 20, 40, and 80 μg/mL, using three independent series of six replicates per level. Trueness, repeatability, intermediate precision, linearity, selectivity, and accuracy profiles were assessed. LOD and LOQ were estimated using the ICH relationships 3.3σ/S and 10σ/S, based on the mean slope and the standard deviation of the intercepts of three calibration curves.Recoveries ranged from 98.08% to 102.36%, and intermediate-precision CVs ranged from 0.415% to 2.555%. Estimated LOD/LOQ values were 0.6623/2.0069 μg/mL for kojic acid and 0.4201/1.2732 μg/mL for hydroquinone. Mean hydroquinone content did not differ significantly between creams and lotions (Welch p = 0.095). Exceeding 1% kojic acid was not associated with dosage form (Fisher p = 1.000). Hydroquinone exceeded 2% in all 14 products; five also exceeded 1% kojic acid.The method is suitable for compliance-oriented quality control over the validated range. All 14 products were globally non-compliant, precluding logistic regression. The LOD/LOQ values remain estimates requiring experimental confirmation at low concentrations.

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