Malaysian Journal of Analytical Sciences Vol 22 No 1 (2018): 54 - 63

MICROEMULSION ELECTROKINETIC CHROMATOGRAPHY COUPLED WITH DISPERSIVE MICRO-SOLID PHASE EXTRACTION FOR DETERMINATION OF ISOFLAVONES IN SOYBEAN PRODUCTS

(Kromatografi Elektrokinetik Mikro-Emulsi Berganding dengan Pengekstrakan Fasa Pepejal Mikro Serakan bagi Pengenalpastian Isoflavon di dalam Produk Kacang Soya)

Khaulah Ab Rahim¹, Mohd Marsin Sanagi^1,2*, Dadan Hermawan³, Wan Aini Wan Ibrahim^1,2, Aemi Syazwani Abdul Keyon¹

¹Department of Chemistry, Faculty of Science

²Centre for Sustainable Nanomaterials, Ibnu Sina Institute for Scientific and Industrial Research

Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia

³Department of Chemistry, Faculty of Science and Engineering,

Universitas Jenderal Soedirman (UNSOED), Purwokerto, Indonesia

*Corresponding author: marsin@kimia.fs.utm.my

Received: 26 August 2017; Accepted: 27 December 2017

Abstract

A new method based on microemulsion electrokinetic chromatography (MEEKC) coupled with dispersive micro solid phase extraction (D-µ-SPE) was developed for the determination of isoflavones in soy products. D-µ-SPEs of real samples were carried out using multi-walled carbon nanotubes (MWCNTs) as adsorbent prior to MEEKC. Separations of selected isoflavones namely daidzein, genistein and formononetin by MEEKC were carried out using fresh daily-prepared microemulsion background electrolyte (BGE). The optimized MEEKC conditions for the separation of isoflavones were 4 mM borate buffer pH 8.5, 6.6% (w/v) 1-butanol, 0.9% (w/v) sodium dodecyl sulphate, 0.75% (w/v) ethyl acetate, 3% (w/v) acetonitrile at 3 s injection time, 27 kV and 35 °C. Meanwhile, the optimum D-m-SPE conditions were 5 mg of MWCNTs and 300 µL of methanol as desorption solvent. Under the optimized conditions, the developed D-µ-SPE-MEEKC method showed good linearity in the concentration range of 1-10 mg/L with coefficients of determination (r²) > 0.99 and limits of detection of 0.27-0.95 mg/L. The method was successfully applied to the determination of isoflavones in five soybean products namely soy supplement, tofu, tempeh, egg tofu and fujook and good recoveries were obtained in the range of 74.5-112.5% with RSDs of < 3%. The method has proved to be simple and offers low consumption of organic solvent and relatively short analysis time, thus it is a potentially viable green alternative method for extraction and determination of isoflavones in soybean products.

Keywords: microemulsion electrokinetic chromatography, background electrolyte, dispersive micro solid phase extraction, isoflavones, soybean products

Abstrak

Satu kaedah baharu berasaskan kromatografi elektrokinetik mikroemulsi (MEEKC) berganding dengan pengekstrakan fasa pepejal mikro serakan (D-μ-SPE) telah dibangunkan bagi menentukan isoflavon di dalam produk kacang soya. D-μ-SPE sampel sebenar telah dijalankan menggunakan tiub nano karbon dinding berganda (MWCNT) sebagai penjerap sebelum MEEKC. Pemisahan isoflavon terpilih iaitu daidzein, genistein dan formononetin dengan MEEKC telah dijalankan menggunakan mikroemulsi elektrolit latar belakang (BGE) baharu yang disediakan setiap hari. Keadaan optimum MEEKC untuk pemisahan isoflavon ialah 4 mM penimbal borat pH 8.5, 6.6% (w/v) 1-butanol, 0.9% (w/v) natrium dodekil sulfat, 0.75% (w/v) etil asetat, 3% (w/v) asetonitril pada masa suntikan 3 s, 27 kV dan 35°C. Sementara itu, keadaan optimum untuk pengekstrakan ialah 5 mg MWCNT dan 300 µL metanol sebagai pelarut penyaherapan. Di bawah keadaan optimum, kaedah D-µ-SPE-MEEKC yang dibangunkan menunjukkan kelinearan yang baik dalam julat 1-10 mg/L dengan pekali penentuan (r²) > 0.99 dan had pengesanan 0.27-0.95 mg/L. Kaedah D-µ-SPE-MEEKC telah berjaya digunakan dalam penentuan isoflavon di dalam lima produk soya iaitu makanan tambahan soya, tofu, tempe, tauhu telur dan kulit tauhu dengan kadar pengembalian 74.5 – 112.5% dan sisihan piawai relatif (RSD) < 3%. Kaedah ini terbukti mudah dan ia menggunakan pelarut organik yang sedikit dan memberi masa analisis yang cepat, justeru berpotensi sebagai kaedah hijau berdaya saing bagi pengekstrakan dan penentuan isoflavon di dalam produk kacang soya.

Keywords: Kromatografi elektrokinetik mikroemulsi, elektrolit latar belakang, pengekstrakan fasa pepejal mikro serakan, isoflavon, produk kacang soya

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