Isotachophoretic determination of theanine

Abstract

Free amino acids, the key quality components of tea, are contained in higher amounts in higher grade teas. Among free amino acids in tea, the content of theanine, which is the amino acid of the highest amount, shows high correlation to the price of green tea. A capillary isotachophoresis (CITP) method was developed for the analysis of L-theanine in tea and food supplements. The optimized electrolyte system was following: 0.01 mol/l HCl + 0.02 mol/l TRIS + 0.05 % HEC (leading electrolyte), 0.01 mol/ L-valine + barium hydroxide to pH 10 (terminating electrolyte). Good separation of L-theanine from other components of sample was achieved within 20 min. Method characteristics, i.e., linearity (0 -200 mg/l), accuracy (99 ± 2 %), intra-assay (1.5 %), quantification limit (2 mg/l), and detection limit (0.7 mg/l) were determined. Sufficient sensitivity, low labouriousness (extraction only) and low running cost are important attributes of this method. It was proved that the developed method is suitable for the routine analysis of L-theanine in green tea and food supplements containing green tea extract.

Determination of Free Tryptophan in Beer Samples by Capillary Isotachophoretic Method

“…Based on the amphoteric character of amino acids and low mobility in electric field, their separation by ITP in pH 3-10 is difficult (Kovářová et al 2018). However, many authors (Everaerts et al 1976;Kubačák et al 2006;Kvasnička and Krátká 2006;Prest et al 2004; Zgola-Grześkowiak and Grześkowiak 2012) described the application of ITP for amino acid determination and this method appears to be complementary to existing procedures. According to Everaerts et al (1976), if the pH of the leading electrolyte is above 8, most amino acids will have an effective mobility suitable for isotachophoretic separation.…”

“…The progress on analytical applications of ITP is systematically published since 1997 (Gebauer and Boček 1997;Malá and Gebauer 2019). The simple determination of amino acids in different samples by ITP was proposed by some Authors (Jastrzębska et al 2013(Jastrzębska et al , 2015Kubačák et al 2006;Kvasnička and Krátká 2006;Prest et al 2004; Zgola-Grześkowiak and Grześkowiak 2012); however, Trp was not satisfactory separated in the described electrolyte systems. ITP allows for simple and direct analysis of amino acids as well as after their derivatization (Kovářová et al 2018).…”

L-Theanine: properties, synthesis and isolation from tea

“…The system used an untreated fused‐silica capillary column and a built‐in photodiode array detector set at 200, 205, 220, 266 and 280 nm. In addition, theanine has also been determined using isotachophoretic anion‐exchange chromatography with integrated pulsed amperometric detection or enzymatic flow injection analysis 49–51…”

Rapid and selective quantification of l-theanine in ready-to-drink teas from Chinese market using SPE and UPLC-UV

“…A number of analytical methods have been developed to determine L-theanine individually, or with other amino acids both in tea compositions and simultaneously in different matrices. These include capillary electrophoretic (Aucamp, Hara, & Apostolides, 2000;Chen et al, 2003;Horie, Mukai, & Kohata, 1997;Kvasnička & Krátká, 2006) and chromatographic methods. L-theanine can be analysed simultaneously with amino acids by high performance liquid chromatographic (HPLC) methods involving pre-column derivatization with o-phthaladehyde, phenylisothiocyanate or dabsyl chloride, and fluorescence and diode array UV detection (Alcázar et al, 2007;Liang, Ma, Lu, & Wu, 2006;Syu, Lin, Huang, & Lin, 2008;Thippeswamy et al, 2006;Van der Pijl, Chen, & Mulder, 2010;Ying, Ho, Chen, & Wang, 2005).…”