Large-Volume Sample Staking of Rice Polyphenols Prior to Their Determination by Non-aqueous Capillary Electrophoresis
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Large-Volume Sample Staking of Rice Polyphenols Prior to Their Determination by Non-aqueous Capillary Electrophoresis Sajida Parveen 1 & Saima Q. Memon 2 & Ali N. Siyal 2 & Najma Memon 3 & Muhammad Y. Khuhawar 1
Received: 21 August 2015 / Accepted: 22 December 2015 # Springer Science+Business Media New York 2016
Abstract A rapid non-aqueous capillary electrophoretic (NACE) method for the separation of (−)-epicatechin (EPI), (+)-catechin (−CAT), kaempferol (KAE), quercetin (QUR), naringanin (NAR), ferulic acid (FA), and p-coumaric acid (p-CA) has been developed and applied to the determination of these compounds in different rice varieties. All seven compounds were separated on capillary of 50 μm × 68 cm (60-cm effective length) using 20 mmol L−1 borate buffer of pH 9.0 and 5 % acetonitrile in methanol. Large-volume sample stacking (LVSS) technique was optimized and used to preconcentrate non-detectable polyphenols of white polished rice. Rice extracts were concentrated on-line by LVSS prior to separation by non-aqueous capillary electrophoresis. An improvement of 10–55 times in detectability was achieved with injection at 50 mbar for 30 s followed by voltage inversion (−20 kV) for 5 s. Linear calibration range of 1–300 μg L−1 and 0.01–60 μg L−1 was observed for NACE and NACE-LVSS method respectively, with the detection limit of 0.33–2.0 and 0.006–0.19 μg L−1. Good reproducibility with standard deviations of less than 5 % was achieved. Polyphenol contents of different rice varieties were determined using developed method.
* Saima Q. Memon [email protected]; [email protected]
1
Institute of Advance Research Studies in Chemical Sciences, University of Sindh, Jamshoro 76080, Pakistan
2
M. A. Kazi Institute of Chemistry, University of Sindh, Jamshoro 76080, Pakistan
3
National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, University of Sindh, Jamshoro 76080, Pakistan
Keywords Polyphenol separation . Antioxidants . Rice . Non-aqueous capillary electrophoresis . Large-volume sample staking
Introduction Phytochemicals are naturally accruing compounds which are widely distributed in fruits, veggies, and teas (Ignat et al. 2011; Fardet et al. 2008) and have many health-promoting properties, e.g., antioxidant, antibacterial, antiinflammatory, antiallergic, and antithrombotic ones. Rice (Oryza sativa L.), being one of the most consumed cereals in many parts of the world, sustains an important role in the relation between diet and health (Iqbal et al. 2005). Pakistan is the fourth largest rice exporter and shares area of 2.31 million hectares with the production of 5.54 million tons (FBSGP 2013). Several compounds with antioxidant activity have been identified in rice, including phenolic compounds such as tocopherols, tocotrienols, and −oryzanol (Iqbal et al. 2005). There are a number of methods available for determination of phenolic compounds and their antioxidant activities in cereal, fruit, and vegetables such as thin-layer chromatography, open-column chromatography (Amarow
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