Solvent and temperature effects of accelerated solvent extraction (ASE) coupled with ultra-high pressure liquid chromatography (UHPLC-DAD) technique for determination of thymoquinone in commercial food samples of black seeds (Nigella sativa)

Black seeds (Nigella sativa), is considered a traditional folk medicine in Saudi Arabia where it is widely available in the form of food supplements with limited information warranting its quality. This study aims to develop an effective and reliable method of black seeds evaluation and standardization in terms of Thymoquinone (THQ), obtained from various geographical sources i.e. Pakistan (PK), Saudi Arabia (SA) and India (I). Accelerated solvent extraction (ASE) was utilized for the first time to extract whereas Ultra High pressure liquid chromatography (UHPLC-DAD) was used to quantify THQ. Inductively coupled plasma mass spectrometry (ICP-MS) was used for elemental analysis of the samples. An ideal temperature (70 degrees C) and solvent (n-hexane) with extraction yield of 97.30% +/- 3.98 was observed. In the case of commercial food samples an extraction yield and %recovery within a short time (42 +/- 2 min) using least amount of solvent (49.5 +/- 2 ml) was observed; SA (18.22 g; 91.1%) > PK (17.32 g; 86.6%) > I (16.33 g; 81.65%). UHPLC resulted a RT of 3.29 min for THQ with concentration (ng/ml) in the samples as; SA, 34410.36 > PK, 7778.95 > I, 4106.43. Elemental analysis revealed an order of SA > I > PK for tested elements. ASE resulted a high extract yield as compared to traditional methods of extraction whereas ASE-UHPLC/DAD showed a rapid and sensitive method of THQ quantification and quality determination in market available food samples for black seeds.