Determination of the sunscreen 2-ethylhexyl-p-methoxycinnamate in cosmetics by reversed-phase HPTLC with ultraviolet absorption densitometry on preadsorbent plates

A quantitative high-performance thin-layer chromatographic (HPTLC) method has been developed for determination of the sunscreen ingredient 2-ethylhexyl p-methoxycinnamate (EHMC) in cosmetics using preadsorbent reversed-phase (RP) C18 chemically bonded silica gel plates with fluorescent indicator and scanning densitometry of fluorescence-quenched zones of samples and standards. Various brands of cosmetic were analyzed to assess the relationship between EHMC content and the SPF number stated on the label. The accuracy of the analyses was validated by performing recovery studies with fortified samples containing similar ingredients but no EHMC. Precision was determined by analyzing replicate samples. It was found that the amount of EHMC in the products tested ranged from 2.71-6.87%. The relative standard deviations for determination of EHMC averaged 6.80% with a range 1.40-9.87% (n = 4). Average recoveries from two fortified samples were 101.7 and 104.0%.