Investigation of Acetonitrile-Based Mobile Phase Variables Influencing the HPLC-UV Separation of Methylparaben and Propylparaben in Pharmaceutical Syrups

Abstract

A rapid, selective RP‑HPLC method was developed and validated for simultaneous determination of methylparaben (MP) and propylparaben (PP) in pharmaceutical syrups. Separation was achieved on a Kromasil C18 column (150×4.6 mm, 5 µm) with isocratic elution (acetonitrile–water 60:40 v/v, pH 6.5) at 1.0 mL/min and 30 °C, with UV detection at 254 nm. MP and PP eluted at 2.5 and 3.6 min, respectively, with good symmetry. The effects of mobile‑phase composition, flow rate, pH, and temperature were evaluated by ANOVA; composition, flow rate, and pH were significant, while temperature was not, with composition being the dominant factor.

Validation per ICH Q2(R2) showed excellent linearity (R² > 0.999 for MP, > 0.996 for PP) over 1.5–30 µg/mL and 0.5–10 µg/mL, intra‑ and inter‑day RSDs < 2.0%, and recoveries of 99.20–101.03%. LODs were 0.1 and 0.05 µg/mL, LOQs 0.3 and 0.1 µg/mL for MP and PP. Application to commercial syrups gave MP concentrations of 0.11–0.15 mg/mL and PP of 0.01–0.03 mg/mL.