Simultaneous RP-HPTLC Method for Determination of Levodopa, Carbidopa, and Entacapone in Combined Tablet Dosage Form

Abstract

A simple, rapid, specific, and accurate reverse-phase high-perfor mance thin-layer chromatography (RP-HPTLC) method was devel oped and validated for simultaneous quantification of levodopa, carbidopa, and entacapone in their combined dosage form. Due to the structural similarity between levodopa and carbidopa, and vast difference in their polarity with that of entacapone, it is very challenging to carry out the simultaneous estimation of all three drugs together. In the developed method, chromatography was performed on TLC plates with precoated silica gel 60 RP-18 F254 using acetonitrile–n-butanol–water–triethylamine (0.5:9.5:1:0.001, v/v/v/v), pH adjusted to 3.6 with o-phosphoric acid, as the mobile phase. Densitometric evaluation was performed at 282 nm. The RF values were 0.46, 0.64, and 0.87 for levodopa, carbidopa, and entacapone,respectively. The polynomial regression data for the calibration plots showed good linear relationship in the concentration range 300–1500 ng per spot for levodopa, 200–1000 ng per spot for car bidopa, and 200–2000 ng per spot for entacapone. The suitability of this HPTLC method for quantitative determination of drugs was proved by validation in accordance with the requirements of the International Conference on Harmonization (ICH) guidelines (Q2B).