Determination of lignans in Wuweizi by using magnetic bar microextraction and HPLC

J. Sep. Sci. 2013, 36, 3527–3533 3527

Jiayuan Shi1Xu Xu1

Xinyu Li2Chao Liu3

Mingyuan Shao1

Huijie Zhang1

Zhibing Wang1

Hanqi Zhang1

Yanfu Huan1

1College of Chemistry, JilinUniversity, Changchun, P. R.China

2Department of Laboratory,China-Japan Union Hospital,Jilin University, Changchun,P. R. China

3Department of Plastic andReconstructive Surgery, FirstHospital, Jilin University,Changchun, P. R. China

Received June 16, 2013Revised August 20, 2013Accepted September 08, 2013

Research Article

Determination of lignans in Wuweiziby using magnetic bar microextractionand HPLC

In this paper, a magnetic bar microextraction was developed to extract schisandrin A,schisantherin A, and deoxyschizandrin from Wuweizi. The analytes were determined byHPLC. A stainless-steel wire was inserted into the hollow of the hollow fiber to make themagnetic bar. The bar can be used to stir the extraction system and extract the analytes, andwas isolated from the extract system by magnetic force. Several experimental parameters,including type and volume of extraction solvent, the number of magnetic bars, extractiontemperature and time, stirring speed and NaCl concentration were investigated and op-timized. The LODs for schisandrin A, schisantherin A, and deoxyschizandrin were 0.14,0.06, and 0.10 �g/mL, respectively. The recoveries were in the range of 70.90–106.67% andthe RSDs were < 8.84%. Compared with ultrasound-assisted and Soxhlet extraction, whenthe present method was applied, the extraction time was shorter, the sample amount wassmaller, and the consumption of organic solvent was lower.

Keywords: HPLC / Lignans / Magnetic bar microextraction / Traditional Chinesemedicine / WuweiziDOI 10.1002/jssc.201300635

1 Introduction

The ripe fruits of Schisandra chinensis (Turcz.) Baill.(S. chinensis) and Schisandra sphenanthera Rehd. et Wils.(S. sphenanthera) are named as Wuweizi [1], which has beenwidely used as a traditional Chinese medicine for severalthousand years. The contents of the effective components inthe S. chinensis and S. sphenanthera are quite different [2]. Inthe Chinese Pharmacopoeia (2010 edition), the fruits of the S.chinensis and S. sphenanthera have been officially listed as twodifferent crude drugs [3]. Extensive studies have indicated thatthe major effective components of Wuweizi are lignans [4–6],which have a dibenzocycooctadiene skeleton and highabsorption of UV radiation [7]. The lignans have been provento prevent liver injuries, stimulate liver regeneration, andexhibit anti-oxidant, antitumor, anticarcinogenic, anti-HIVactivities, and central nervous system reimbursement [8–14].Therefore, it is significant to develop an effective method fordetermination of the lignans. HPLC has some advantages, in-cluding high separation efficiency, high detection sensitivity,and broad application range. Thus, HPLC is very appropriate

Correspondence: Professor Yanfu Huan, College of Chemistry,Jilin University, Qianjin Street 2699, Changchun 130012, P. R.ChinaE-mail: [email protected]: +86-431-85112355

Abbreviations: HF, hollow fiber; HF-LPME, hollow-fiber-based liquid-phase microextraction; LPME, liquid-phasemicroextraction; MBME, magnetic bar microextraction; SE,Soxhlet extraction; UE, ultrasonic extraction

and convenient for the determination of the lignans basedon the UV absorption of the lignans in Wuweizi [15, 16].

Traditional extraction methods, such as solvent extrac-tion, maceration extraction, Soxhlet extraction (SE), and circu-lation reflux extraction have been widely applied for extractionof lignans from Wuweizi [17–19]. However, these conven-tional methods are usually laborious and time consuming, re-quire a large amount of toxic and hazardous organic solventsand additional clean-up [20]. Several new methods for theextraction of lignans have been reported, including supercrit-ical fluid extraction, pressurized liquid extraction, microwaveextraction, and ultrasonic extraction (UE) [21–24]. Up tonow, hollow fiber (HF) based magnetic bar microextraction(MBME) for the simultaneous extraction of the major effec-tive constituents including schisandrin A, schisantherin A,and deoxyschizandrin from Wuweizi has not been reported.

HF liquid-phase microextraction (LPME) [25–27], com-bining extraction and preconcentration in a single step priorto direct injection analysis, was introduced by Pedersen-Bjergaard and Rusmussen in 1999 [28,29]. When the methodwas applied, the organic solvent consumption was reduced,and selectivity was improved [30]. Two hollow-fiber-basedliquid-phase microextraction (HF-LPME) configurations canbe used: two phase and three phase. In two-phase HF-LPME,which is applied in this work, the target analytes were ex-tracted from the aqueous sample into the organic solventlocated in the pores of the wall and the hollow of the hol-low fiber. The small pore size prevents large molecules andparticles present in the donor solution from entering the ac-cepter phase and at the same time, most macromolecules donot enter the hollow fiber because they are not soluble in the

C© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com

3528 J. Shi et al. J. Sep. Sci. 2013, 36, 3527–3533

Figure 1. Chemical structures of (A)schisandrin A, (B) schisantherin A, and (C)deoxyschizandrin.

organic phase present in the pores, thus yielding very cleanextracts [31–33]. But the extraction and separation process iscomplicated. So, it is necessary to simplify HF-LPME method.

In this work, HF-based MBME was applied for the simul-taneous extraction of schisandrin A, schisantherin A, and de-oxyschizandrin from Wuweizi. The magnetic bar is cheaplymanufactured and easily isolated from the sample matrix withan external magnetic field. The present method integrates theextraction and stirring in the same device and is extremelysimple. To evaluate the new extraction method, UE and SEwere applied as reference methods.

2 Materials and methods

2.1 Chemicals and reagents

The standards, including schisandrin A, schisantherin A, anddeoxyschizandrin, were obtained from the National Institutefor the Control of Pharmaceutical and Biological Products(Beijing, China). Chromatographic grade acetonitrile andmethanol were purchased from Fisher (Pittsburgh, PA, USA).The structures of the analytes are shown in Fig. 1. The ana-lytes are hydrophobic compounds and can easily dissolve inlow polarity organic solvents. The standard stock solutionsof the analytes were prepared by dissolving the compoundsin acetonitrile, and stored at 4�C. The working standard so-lutions were prepared by diluting the stock solutions withacetonitrile. Pure water was obtained with a Milli-Q watersystem (Millipore, Billerica, MA, USA). All other analyti-cal reagents were purchased from Beijing Chemical Factory(Beijing, China). Q 3/2 Accurel polypropylene hollow fiber(600 �m inner diameter, 200 �m wall thickness, and 0.2 �mpore size) was purchased from Membrana (Wuppertal, Ger-many). A stainless-steel wire (505 �m outer diameter) wasinserted into the hollow of the hollow fiber.

2.2 Instrument and chromatographic conditions

A Shimadzu LC-20A HPLC system (Shimadzu, Kyoto, Japan)equipped with an SPD-20A UV detector was used. Chromato-graphic separation was performed on an XDB-C18 column(150 × 4.6 mm id, 5 �m; Agilent, Palo Alto, CA, USA). We

used a KQ-100DE ultrasonic generator (Kunshan, Jiangsu,China).

The mobile phase consisted of water (A) and acetoni-trile (B). The gradient condition was as follows: 0–10 min,60% B; 10–15 min, 60–80% B; 15–20 min, 80% B; 20–25 min,80–60% B. The flow rate of the mobile phase was kept at0.65 mL/min. The injection volume of the sample solutionwas 10 �L, and temperature of the column was controlled at35�C. The detection wavelength was set at 230 nm.

2.3 Sample preparation

Four samples (samples 1–4) cultivated in different areas werepurchased from local drugstores, samples 1 and 2 belong toS. chinensis, and samples 3 and 4 belong to S. sphenanthera.The dried samples were milled by pulverizer, passed througha 60 mesh sieve, dried thoroughly in a cabinet drier at 40�Cfor 48 h and then stored in a desiccator. Sample 1 was usedin all experiments except for the experiments mentioned inSections 3.2.3 and 3.3.

2.4 Magnetic bar microextraction

Five milligrams of sample power was weighed accurately andplaced in a 20 mL extraction vessel. One Hundred microlitersof methanol was added into the vessel, diluted with deionizedwater to 1 mL, and then mixed ultrasonically for 3 min. Thehollow fiber and the stainless-steel wire were manually cutinto 1.2 cm pieces, washed with acetone in an ultrasonic bathto remove impurities, and dried in the air. Then the magneticbar was prepared by inserting the stainless steel wire intothe hollow of the hollow fiber. The resulting fiber piece wasimmersed in toluene for 1 min in order to impregnate poresof the fiber wall, and rinsed with water in order to removethe extra toluene from the surface of the fiber. The preparedhollow fiber is referred to as a magnetic bar (Fig. 2A). Eightmagnetic bars were placed into the extraction vessel and thevessel was placed on a magnetic stirrer. The extraction wasperformed at 30�C, and the sample was stirred at 500 rpm.After 15 min of extraction, the solution in the vessel wasremoved and the magnetic bars were desorbed with 600 �L


J. Sep. Sci. 2013, 36, 3527–3533 Liquid Chromatography 3529

Figure 2. Magnetic bar (A) and extrac-tion procedure (B).

of acetonitrile in an ultrasonic bath for 3 min. The resultingsolution was dried under nitrogen steam, and the residuewas dissolved in 200 �L acetonitrile. The resulting solutionwas filtered through a 0.22 �m membrane filter, and thefiltrate was referred to as the sample solution. The extractionprocedure is shown in Fig. 2B.

2.5 Ultrasonic extraction

A 0.25 g of sample power was placed in a 50.00 mL volumetricflask and 25.00 mL of 80% methanol was added accuratelyinto the flask. Then UE was performed at 100 W for 30 min.The extract was diluted to 25.00 mL with 80% methanol. Theresulting solution was filtered through a 0.22 um membranefilter and referred to as the sample solution.

2.6 Soxhlet extraction

0.5 g of sample power was placed in a flask of the Soxhletextractor, and 100 mL 80% methanol was added into the flaskof the Soxhlet extractor. The extraction was carried out for 4 h.Then the resulting solution was diluted to 250.00 mL with80% methanol. The resulting solution was filtered through

a 0.22 �m membrane filter and referred to as the samplesolution.

3 Results and discussion

3.1 Optimization of MBME

In order to obtain a high extraction yield, the effects of severalexperimental parameters were investigated, including typeand volume of extraction solvent, dispersion time and thenumber of magnetic bars, extraction temperature and time,stirring speed, and NaCl concentration. All the experimentswere performed in triplicate.

3.1.1 Type of extraction solvent and the number of

magnetic bars

There are several rules for the selection of organic solvent: thepolarity of the organic solvent should be similar to that of thepolypropylene fiber so that it can be easily immobilized withinthe pores of the fiber; the solvent must be immiscible withwater in order to prevent solvent loss during the extraction;and the solvent should have low volatility. Based on theserules, five organic solvents, including 1-octanol, toluene,



Figure 3. Effect of extraction condi-tions.(a) Schisantherin A, (b) Deoxyschizan-drein, (c) Schisandrin A.(A) n-hexane, (B) 1-octanol, (C) toluene,(D) ethyl acetate, (E) cyclohexane.

n-hexane, cyclohexane, and ethyl acetate were investigated.The extraction yields obtained with the extraction solventsare shown in Fig. 3. The results show that the extractionyields obtained with toluene are higher than those obtainedwith other solvents. The main reason may be that the polarityof toluene and target analytes is similar, there are hydropho-bic effects and �–� interactions between the benzene ringsof the analyte and toluene. Therefore, toluene was chosen asthe extraction solvent in this investigation.

The pores of the hollow fiber were impregnated withextraction solvent. In order to evaluate the influence of ex-traction solvent volume on extraction yield, the effect of thenumber of magnetic bars was studied. Figure 3 shows theeffect of the number of the magnetic bars on the extractionyields. It can be seen from the figure that when the numberof the magnetic bars increases from 2 to 8, the extractionyields of three target analytes increase, and when the num-ber increases from 8 to 10, the extraction yields decrease.Thus, eight magnetic bars were selected in the subsequentexperiments.

3.1.2 Volume of disperser and dispersion time

The target analytes could be dissolved well with the help of dis-perser. In this experiment, methanol was used as disperser.The volume of disperser can directly influence the solubilityand the extraction yield of target analytes. The effect of dis-perser volume was studied and the results shows that whenthe methanol was 100 �L and water was 900 �L, the extractionyields of the three target analytes were the highest. Therefore,the volume of disperser was chosen as 100 �L.

Ultrasonic dispersion is beneficial to the dispersion ofthe sample in solution and the transfer of target analytes tothe aqueous phase from solid samples. However, too long adispersion time can result in the loss of the disperser. So,the dispersion time was studied from 0 to 10 min and theresults indicated that the extraction yields of three target an-alytes increased with the time in the range of 0–3 min, and

then decreased with the increase of the time in the range of3–10 min. Therefore, 3 min was selected as the dispersiontime in the following experiments.

3.1.3 Effect of stirring speed

Stirring speed played an important role in stirring extraction.Stirring the sample solution could enhance extraction rateand reduce extraction time because the thermodynamic equi-librium can be achieved more rapidly. However, high stirringspeed can generate some problems, such as promotion of sol-vent evaporation and production of air bubbles on the surfaceof the hollow fiber. The effect of stirring speed ranging from300 to 700 rpm was studied. The results are shown in Fig. 3,and it was observed that extraction yields increase with thestirring rate up to 500 rpm. Thus, a stirring speed of 500 rpmwas chosen for subsequent experiments.

3.1.4 Effect of extraction time

Extraction is a dynamic process and the target analytes istransferred from the sample into the extraction solvent. Theextraction yield will be the largest when the dynamic equilib-rium is reached. It needs time to achieve the dynamic equi-librium. Too long extraction time can result in the loss of theextraction solvent and the decrease of the extraction yields.However, when the extraction time is too short, the partitionequilibrium of the target analytes in the water and the extrac-tion solvent has not yet reached. The influence of extractiontime (5, 10, 15, 20, 25 min) was tested and the experimentalresults are shown in Fig. 3. At first, the extraction yields in-crease with time, and then decreases with the increase of timewhen the time is longer than 15 min. The decrease of extrac-tion yield can be due to potential solvent loss with the increaseof extraction time. Based on these observations, 15 min waschosen to be the extraction time.



Table 1. Regression equations, linear ranges, LODs, and LOQs for determining three analytes

Analyte Linear range (�g/mL) Regression equation Correlation coefficient LODs (�g/mL) LOQs (�g/mL)

Schisandrin A 0.49–976.00 A = 54224C + 44216 0.9999 0.14 0.45Schisantherin A 0.25–500.00 A = 76203C − 8781 0.9999 0.06 0.21Deoxyschizadrin 0.35–350.00 A = 74337C + 17653 0.9999 0.10 0.32

3.1.5 Effect of extraction temperature

In order to investigate the effect of extraction temperatureon the extraction yield, various extraction temperatures weretested from 15 to 35�C. The experimental results are shownin Fig. 3. The extraction yields of the three target analytesincreased with increase of the extraction temperature, and theextraction yields reached the highest level at 30�C. When theextraction temperature was greater than or less than 30�C, theextraction yields decreased. The low extraction temperaturecan result in the decrease of diffusion rate of the analytes intwo phases, and high extraction temperature results in thedissolution and volatilization loss of the extraction solvent.So, 30�C was adopted for further experiments.

3.1.6 Effect of NaCl concentration

The effect of salt concentration on the extraction yield wastested by increasing NaCl concentration from 0 to 30% w/v.The extraction yields increase with the NaCl concentrationfrom 0 to 5%. The reason may be that the addition of NaClcould give rise to the increase in the ionic strength of thesolution and the decrease of the solubility of the analytes inthe aqueous phase. The extraction yields decrease with theincrease of NaCl concentration from 5 to 30%. The reasonmay be that the viscosity of aqueous solution increases withthe increase of salt concentration, which results in difficultmass transfer. Thus, 5% NaCl was used in the subsequentexperiments.

3.2 Method validation

The method was evaluated in terms of the linearity, LOD andLOQ, inter-, and intraday precision and recovery.

3.2.1 Analytical performances

The stock solution containing the three analytes was diluted tofive different concentration levels for construction of the cal-ibration curves, which were constructed by plotting the peakareas versus the concentrations of the analytes. The linear re-gression equations, linear ranges and correlation coefficientswere listed in Table 1. All the LODs and LOQs indicated inTable 1 were determined at a S/N of 3 and 10, respectively.

The precision was evaluated by measuring intra- and in-terday RSDs. The intraday precision was obtained by ana-lyzing sample 1 five times within one day. The results are

Table 2. The intra- and interday precision of the analytes

Analyte Intraday (n = 5) Interday (n = 5)

Extraction RSD(%) Extraction RSD(%)yield (�g/mg) yield (�g/mg)

Schisandrin A 5.50 2.51 5.60 2.00Schisantherin A 0.38 2.63 0.39 1.42Deoxyschizadrin 0.70 5.71 0.74 4.71

listed in Table 2, and the RSDs of schisandrin A, schisan-therin A and deoxyschizandrin were 2.51, 2.63, and 5.71%.The interday precision was evaluated by analyzing the sample1 three times each day over five consecutive days. The resultsobtained are also listed in Table 2, and the RSDs are 2.00%for schisandrin A, 1.42% for schisantherin A, and 4.71% fordeoxyschizandrin.

3.2.2 Analysis of samples

In order to validate the applicability of the newly establishedmethod, some samples were analyzed under the optimalconditions. The analytical results are listed in Table 3. Thespiked samples were analyzed and the results are also shownin Table 3. It can be seen that the recoveries range from70.90–106.67% with RSDs ranging from 1.74–8.84%. Theresults show that this method is suitable for determinationof schisandrin A, schisantherin A, and deoxyschizandrin

Table 3. The extraction yields and recoveries of the analytes

Sample Analyte Original Spiked Found Recovery RSD(�g/mg) (�g/mg) (�g/mg) (%) (%)

1 Schisandrin A 5.50 5.61 11.31 103.60 4.56Schisantherin A 0.38 0.40 0.72 85.00 2.94Deoxyschizadrin 0.70 0.80 1.39 86.25 2.51






Figure 4. Chromatograms of the stan-dard solution (A) and the extract ofsample 1 (B).

in Wuweizi. The HPLC chromatograms of the standardsolution (A) and the extract of sample 1 (B) are shown inFig. 4.

3.3 Comparison of the present method with other

methods

To evaluate the present method, UE and SE were investigated.Sample 2 was used. The results are listed in Table 4. The

results indicate that the yields obtained by the three methodsare similar. Some other extraction methods reported inliterature, including liquid–liquid extraction [34], SPE [35],and LPME [36], were compared with the present method,and the results are also presented in Table 4. Compared withUE, SE and the reported methods, when the present methodwas applied, the volume of the organic extraction solventwas smaller, the extraction time was much shorter, and thesample amount was smaller. Considering the advantages,MBME should be a satisfactory method.

Table 4. Comparison of the present method with other extraction methods

HF-LPME UE SE LLE SPE LPME

Extraction yield Schisandrin A 6.38 ± 0.14 6.54 ± 0.14 6.60 ± 0.04 — — —(mean ± SDa), �g mg−1) Schisantherin A 0.45 ± 0.01 0.49 ± 0.02 0.47 ± 0.02 — — —

Deoxyschizadrin 0.98 ± 0.03 0.91 ± 0.04 0.87 ± 0.01 — — —Extraction time (min) 15 30 240 30 30 70Sample amount (mg) 5 250 500 — — 400Extraction solvent Toluene Methanol Methanol Dichloromethane Dichloromethane MethanolSolvent volume (mL) 0.10 50 250 15 50 20Reference This work This work This work [34] [35] [36]

a)Standard deviation (n = 5).LLE, Liquid–Liquid extraction.



4 Concluding remarks

In this paper, MBME was established for the simultaneous ex-traction of three active compounds in Wuweizi. The stainless-steel wire was inserted into the hollow of the hollow fiber, andthe resulting magnetic bar was used to stir the extraction sys-tem and extract the analytes. The bar is easy to isolate from theextraction system by magnetic separation. There was no sig-nificant difference in the extraction yields obtained with UE,SE, and the MBME method. However, the present methodhas some advantages in terms of extraction time, the amountof sample and consumption of organic solvent. The resultsindicated that MBME can serve as an effective and practi-cal method for extraction of active compounds in traditionalChinese medicine.

The authors have declared no conflict of interest.

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Determination of lignans in Wuweizi by using magnetic bar microextraction and HPLC