Densitometric HPTLC methods for qualitative and quantitative analysis of carvone, dillapiole, methylparaben and propylparaben in dill, caraway seeds and pharmaceutical formulations utilizing normal and reversed-phase silica gel plates

The monoterpene ketone (4S)-(+)-carvone is found naturally in many essential oils such as caraway (Carum carvi) and dill (Anethum graveolens) seeds. Popular marketed baby formulas for relief of colic contain dill or caraway oils or extracts. In attempts to use HPTLC for estimation of carvone in such preparations as well as dill and caraway oils or extracts two methods were developed. Some formulations showed two prominent spots identified as methylparaben and propylparaben spectroscopically after chromatographic purification. Method I was developed and validated with 10 × 20 cm glass-backed plates coated with 0.2 mm layers of silica gel 60 F₂₅₄ using n-hexane ethyl acetate (9:1 v/v) as developing system. The used system resulted in sharp and symmetrical peak at Rf value of 0.34±0.02 and linearity were found in range 100-800 ng/spot (R2 = 0.9986) for carvone. However, in case of dill seeds extract an overlapping spot was detected and carvone could not be estimated properly. Chromatographic purification and spectroscopic analysis enable the identification of the overlapping spot as dillapiole. Consequently, method II was carried out with 10 × 20 cm glass-backed plates coated with 0.2 mm layers of RP-18 silica gel 60 F254 using methanol-water (8:2 v/v) as mobile phase. Using method II simultaneous determination of carvone, dillapiole, propylparaben and methylparaben was achieved. The R_f values were 0.39 ± 0.04, 0.28 ± 0.04, 0.51 ± 0.02 and 0.59 ± 0.02 and linearity were found in range 100-800 ng/spot (R² = 0.9982), 100-1000 ng/spot (R² = 0.9984), 50-1000 ng/spot (R² = 0.9984) and 50-1000 ng/spot (R² = 0.9983) for carvone, dillapiole, methylparaben and propylparaben respectively. The two methods were found to be simple, precise, specific, and can be applied for standardization of different pharmaceutical formulations.