Use of anion-exchange membrane extraction for the high-performance liquid chromatographic analysis of mustard seed glucosinolates

A new one-step extraction using anion-exchange membranes for the HPLC determination of glucosinolates in mustard seeds is reported. The exchange of glucosinolates on the membranes was studied using sinigrin in solutions and sinigrin added as an internal standard to seeds of yellow mustard. By varying time of extraction, membrane size, and sample size, the optimal conditions for maximum glucosinolate recovery were determined and the following procedure was adopted: 0.2 g of ground mustard seeds are heated in 20 mL of boiling water for 5 min. After cooling, samples are transferred to plastic centrifuge tubes, 9-cm(2) membranes are added, and suspensions are shaken on a mechanical shaker for 2.5 h. Glucosinolates are then eluted from the membranes with 25 mL of 1 N KCl by shaking again for 2.5 h. Using this procedure, the sinigrin extraction from solutions and from mustard seeds was linear with 80% recovery. Seeds of yellow, brown, oriental, and Indian mustard were analyzed by this procedure; excellent reproducibility, with coefficients of variation in the range 1.0-4.3% were obtained. This method offers a simple and inexpensive alternative to complicated and tedious procedures for glucosinolate isolation/purification required for chromatographic determinations.