Chinese Chemical Letters  2015, Vol.26 Issue (12): 1470-1477   PDF    
Porous boronate affinity monolith for on-line extraction coupled to high-performance liquid chromatography for sensitive analysis of heterocyclic aromatic amines in food samples
Qian-Chun Zhanga,b, Ying-Yi Chenga, Gong-Ke Lia , Xiao-Hua Xiaoa     
a School of Chemistry and Chemical Engineering, Sun Yat-sen University, Guangzhou 510275, China;
b School of Biology and Chemistry, Xingyi Normal University for Nationalities, Xingyi 562400, China
Abstract: A novel on-line solid-phase microextraction-high-performance liquid chromatography (SPME-HPLC) system was developed for the determination of heterocyclic aromatic amines (HAAs) in food samples. A poly(vinylphenylboronic acid-co-ethylene glycol dimethacrylate) polymer monolith was prepared for on-line efficient extraction and large-volume injection was used to increase the sensitivity of detection. The polymermonolith, based on a ternary porogen, was prepared by in situ polymerization of vinylphenylboronic acid (VPBA) and ethylene glycol dimethacrylate (EGDMA) in a fused-silica capillary column. It showed good permeability, high extraction capacity, and high selectivity. The column-tocolumn reproducibility was satisfactory, and the enrichment factors for HAAs were 3746-7414. Conditions influencing the on-line extraction efficiency, including pH of sample solutions, flow rate of extraction and desorption, and desorption volume, were investigated. The proposed method had low limit of detection (0.10-0.15 ng/L) and good linearity. Trace HAAs in roast beef and lamb samples were determined, and the amounts of 2-amino-3-methylimidazo[4,5-f]quinoline, 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, 2-amino-3,4,8-trimethylimidazo[ 4,5-f]quinoxaline, and 2-amino-3,4,7,8-tetramethyl-3H-imidazo[4,5-f]quinoxaline in these samples were 0.235-2.08 ng/g. The recoveries for the five HAAs ranged from74.3% to 119%, and the relative standard deviation (RSDs) were less than 8.2%. The results showed that the proposed on-line method was highly sensitive for monitoring HAAs in different food samples.
Key words: Boronate affinity polymermonolith     On-line extraction     Heterocyclic aromatic amine     Sensitive analysis     Food sample    
1. Introduction

Diet plays a vital role in maintaining human health,many epidemiological studies have been carried out the cause and effect relationship between diet and disease (30%-40% of cancers are related to diet),especially harmful substances are present in food [1, 2]. The International Agency for Research on Cancer (IARC) considers some heterocyclic aromatic amines (HAAs) as potential human mutagens and carcinogens with trace quantities (ng/g level) in food samples [3, 4]. Thus,the issue of HAA food safety is receiving increasing attention. It has been found that the concentration of HAAs in food depends on various factors,such as meat types,cooking parameters (temperature,time,equipment, and heat transfer),water activity,creatine concentration,type of carbohydrate,and free amino acid content [5]. In order to approximate the amounts of HAAs ingested and their threat to human health,it is highly essential to measure HAA contents in variousmeatproducts.Thus,it isimportant todevelopandvalidate a sensitive,specific,non-invasive method for the biomonitoring and risk assessment of HAA exposure. Although long-term exposure to carcinogenicHAAs infoodsamples canbe assessed,measuringHAAs is difficult because their concentrations are often very low.

It is essential to quantify the amounts of HAA in foods by means of reliable and quantitative methods. Several investigations have been conducted to determine parent HAAs and their metabolites in meat,urine,plasma,hair,and human milk [6, 7, 8, 9, 10, 11] using gas chromatography-mass spectrometry (GC-MS) [12, 13, 14],liquid chromatography-MS (LC-MS) [15, 16],LC-MS/MS [17, 18] and high-performance liquid chromatography (HPLC) with different detectors [8, 19, 20, 21, 22]. Among them,LC-MS or GC-MS were highly selective,sensitive,and powerful for the determination of HAAs. However,time-consuming and laborious sample preparation are often needed in these techniques. On-line sample preparation techniques have gained great interest in recent years. On-line techniques show better sensitivity with good reproducibility,less solvent consumption and sample loss,and fewer analytical errors [23]. The application of on-line solid-phase microextraction (SPME) procedures allows increased sample throughput along with better precision and accuracy. Moreover,higher sensitivities can be achieved,with lower sample volumes owing to the transfer of the total extracted species into the chromatographic system. Thus,the implementation of suitable extraction media and on-line SPME procedures is an important strategy for establishing sensitive and environment-friendly methods for complex sample analysis.

The analysis of HAAs in meat is rather challenging,as the samples have enormous complexity. First,the concentrations of HAAs in real samples are so low (generally ng/g) that,in many cases,the target compounds cannot be detected using traditional analytical methods. Second,there is significant interference from proteins,saccharides,or other small molecules in the matrix, which makes it difficult to clean-up,separate and quantify in real samples. Therefore,various media,such as carbowax [24], propylsulfonyl silica gel [3] and diatomaceous earth [25],have been applied to analysis HAAs [6, 11]. However,the enrichment capacities were limited for HAAs,and the choice of sorbent is critical for improving the enrichment performance. Thus,the development of novel analytical techniques to quantitatively detect trace or ultratrace HAAs is significant and new materials play a crucial role in the selectivity,sensitivity,and accuracy of analytical methods. Boronate-affinity chromatography (BAC) is a powerful technique for the selective isolation and enrichment of compounds,especially cis-diol-containing compounds [26]. BAC has several advantageous features. First,it has broad-spectrum affinity,and thus one boronicacid ligand can capture most,if not all,cis-diol biomolecules,making BAC very useful for global-omics analyses. Second,BAC relies on covalent reactions,its adsorption induced by non-specific interactions can be suppressed or eliminated by choosing appropriate conditions,resulting in high specificity. Third,the capture/release process can be manipulated easily by controlling the pH. Fourth,the desorption kinetics is typically fast,and the analyte carry-over is usually limited. Boronate affinity monolithic columns [27],which combine the virtues of boronate affinity and monolith materials,can be easily produced in situ within the confines of a column or mould from liquid precursors. Such columns show large through-pores, excellent permeability,and fast convective mass transfer,and have attracted considerable attention in recent years [28, 29, 30, 31]. The aim of this work was to develop a new on-line SPME-HPLC method for the determination of HAAs in complicated samples. A boronate affinity monolithic column was prepared by one-step in situ polymerization for SPME,and coupled to HPLC-UV for on-line trace analysis of HAAs in roast beef,and lamb samples.

2. Experimental 2.1. Chemicals and materials

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ),2-amino-3,4- dimethylimidazo[4,5-f] quinoline (MeIQ),2-amino-3,8-dimethylimidazo[ 4,5-f]quinoxaline (MeIQX),2-amino- 3,4,8-trimethylimidazo[ 4,5-f] quinoxaline (4,8-DiMeIQX),and 2-amino-3,4,7,8- tetramethyl-3H-imidazo[4,5-f]quinoxaline (4,7,8-TriMeIQX) were obtained from Toronto Research Chemicals (Toronto,Canada),and their chemical structures are shown in Fig. S1 in Supporting information. Vinylphenylboronic acid (VPBA),ethylene glycol dimethacrylate (EGDMA),and 3-(methacryloxy) propyltrimethoxysilane (&gama;-MPS) were provided by Aladdin Industrial Corporation (Shanghai,China). Azobisisobutyronitrile (AIBN),N,N-dimethyl formamide (DMF),p-xylene,and isooctane were obtained from Damao Chemical Regent Company (Tianjin,China). Water used for HPLC experiments was double distilled and filtered through a 0.22- mm membrane. HPLC grade methanol,acetic acid,and acetonitrile used as the mobile phase were purchased from Dikma (Beijing, China). All other chemicals were of analytical grade.

2.2. Preparation of VPBA-co-EGDMA polymermonolith

Fused silica capillaries (375 μmO.D. and 320 μmI.D.),supplied by Yongnian Optic Fiber Plant (Handan,China),were prepared based on the method of our previous work [32]. Fused-silica capillaries (1000 cm × I.D. 320 μm) were connected to the injection valve and eluted with 1 mol/L NaOH and HCl using a high-pressure pump for 2 h,respectively. After rinsing with purified water and methanol,the capillaries were dried at 150 °C for 2 h. Furthermore,the capillaries were pretreated with &gama;-MPS and cut into 17 cm lengths. VPBA (24.0 mg) and AIBN (7.0 mg) were dissolved in DMF (500 μL),p-xylene (1160 mL), EGDMA (234 μL),and isooctane (500 μL),and sonicated for 10 min at room temperature. After filled with this solution,the pretreated fused silica capillaries were sealed with silicone rubber at each end and placed into an oven at 60 °C for 48 h to initiate the polymerization reaction. Finally,the capillaries were heated at 80 °C for 4 h. The obtained VPBA-co-EGDMA polymermonolith was washed with acetic acid/methanol (1:9,v/v) and acetonitrile/water (3:7,v/v) to remove unreacted reagents and the porogen. The poly (VPBA-co-EGDMA) monolith was cut to a 12.0 cm length.

2.3. On-line enrichment procedures

The poly (VPBA-co-EGDMA) monolithic column was on-line coupled to HPLC. The procedure for HAA enrichment is illustrated in Fig. 1. Briefly,the enrichment process was divided into four steps. (a) Extraction: Valves 1 and 2 were switched to the INJECT position. The sample-solution was driven by water to flow through the SPME column at a flow rate of 200 μL/min. (b) Clean up: Valve 1 was switched to the LOAD position,Valve 2 was set to the INJECT position. The SPME column was cleaned with water at 200 μL/min for 1 min to eliminate residual sample-solution. (c) Desorption: Valves 1 was switched to the INJECT position and valve 2 was set to the LOAD position,the mobile phase flow rate was 100 μL/min to desorb the analytes for full sample loading. (d) Injection: Valve 1 and valve 2 were switched to the INJECT position,the mobile phase flow was 1.00 mL/min,and the analytical pumps were started again. The analysis of HAAs was then carried out based on the on-line SPME-HPLC-UV method.

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Fig. 1.Illustration of the on-line VPBA-co-EGDMA polymermonolith-HPLC system.
2.4. Sample pretreatment

The roast beef,and lamb samples were shredded,and 2.00 g thinly sliced tissue of each sample was used. The extraction was performed in 20 mL of ethyl acetate,1 mL of triethylamine,and 1 mL of 25% ammonia water with ultrasonication (Kunshan, Suzhou,China) at 40 °C for 15 min. The extraction process was repeated after centrifuging the solution for 10.0 min at 10,000 rpm. Subsequently,the extraction solutions were dried with reduced pressure distillation,and then dissolved in 25 mL of acetonitrile at -20 °C. The solution was then centrifuged for 10.0 min at 10,000 rpm. The acetonitrile solution was placed in a 60-mL separating funnel,and then 20.0 mL of n-hexane was added,and the resulting solution was oscillated,the acetonitrile layer was collected and dried with reduced pressure distillation. Then,the residue was dissolved in 20.0 mL of ethyl acetate,as an extraction solvent,and was passed through 2.0 g diatomaceous earth cartridges with 20mL of ethyl acetate used for elution. The ethyl acetate solutionswere combined and driedwith a reduced pressure distillation. Then,the residuewas dissolved in 8.0 mLwater (pH 9.0) for VPBA-co-EGDMA polymermonolith sorptive extraction. Two spiked samples were prepared with 1.6 or 4.8 ng/g of each HAA.

2.5. Chromatographic conditions

HPLC analysis was performed on a Shimadzu LC (Shimadzu, Japan) equipped with three pumps (LC-10A),an ultraviolet detector (SPD-10Avp),an injection valve (Rheodyne model 7725i) with an 8.0 mL sample loop,a switching valve (Rheodyne model 7000),and the acquisition data software Class-VP. The analytical column used was an Atlantis T3 C18 column (150 mm × 4.6 mm I.D.,5 μm) from Waters (Shanghai,China), and a 10.0-mm C18 security guard column from Dikma (Beijing, China) was attached to the analytical column. The mobile phase was acetonitrile/water (pH 3.0,adjusted with 1.5 mmol/L of ammonium acetate and acetic acid). The acetonitrile phase was increased from 5% to 25% (v/v) during 0-20 min. The flow rate was 1.0 mL/min and the HAAs were monitored at 263 nm.

3. Results and discussion 3.1. VPBA-co-EGDMA polymermonolith preparation

Good permeability plays a critical role in on-line SPME techniques. When preparing a boronate affinity polymer monolith, the selection of the porogen is crucial yet difficult because of the polarity of the functionalmonomer,and the polymerization solvent is also a key parameter. Fig. S2 (Supporting information) illustrates the preparation scheme of the VPBA-co-EGDMA polymermonolith. The polymermonolith was prepared based on in our previous work [32]. As an important factor,the polymerization solvents were investigated at first. The VPBA functional monomer was difficult to dissolve in many solvent except DMF and dimethylsulfoxide (DMSO). However,the polymerization was non-homogeneous in DMSO,whereas uniform polymerization was obtained in DMF. As a result,DMF was selected as the polymerization solvent. Moreover, isooctane and p-xylene combined withDMFwere used as the mixed porogens for in situ preparation of monolithic framework for controlling the monolith porous structure. These results indicated that DMF,isooctane and p-xylene were suitable as porogens. In order to examine the permeability of the monolithic column,the backpressure was investigated when the flow rate was set at 100 μL/min. The permeability (KF) values were estimated using the following equation [32].

where KF is the permeability,δ is the flow rate of the pump,h is the solvent viscosity,L is the polymermonolith length,S is the inner cross-sectional area of the polymermonolith,and ΔP is the backpressure. Water was used as the mobile phase with a viscosity of 1 × 10-3 Pa s. The permeability of the VPBA-co-EGDMA polymermonolith was 0.0214,which was lower than that of 1.04 in a previouswork [33]. In addition,the backpressurewas 1.2MPawhen the flow rate was 200 mL/min,could shorten the analytical time. Because the composition of the pre-polymerization mixture has great influence on the monolithic structure,which has a significant influence on the enrichment efficiency,various polymerization parameters,including the ratio of functional monomer to crosslinker and reaction temperature,concerning the polymerization. EGDMA is widely used as a hydrophobic cross-linker in boronate affinity polymer preparation [34, 35],and molar ratios of functional monomer to cross-linker from 1:15 to 1:5 were investigated. The results indicated that the polymermonolith preparedwithVPBAand EGDMA had good uniformity,solvent resistance and extraction ability. The temperature can influence the surfacemorphology,and temperatures of 55.0,60.0,65.0,and 70.0 °C were studied (Table S1 in Supporting information). The results clearly showed that VPBAco- EGDMA polymermonolith was no flaws and good uniformity at 60.0 °C,and this reaction temperature was selected to obtain the polymermonolith with the best mechanical strength.

3.2. Characteristics of the VPBA-co-EGDMA polymermonolith

The infrared spectrum of the VPBA-co-EGDMA polymermonolith was investigated (Fig. 2A). The peak at 3435 cm-1 can be attributed to the O-H stretching vibration of the VPBA hydroxyl group. The band observed at 2953 cm-1 is indicative of C-H stretching,whereas that at 1730 cm-1 is attributed to C=O stretching. The peak around 1454 cm-1 was attributed to the stretching vibration of residual C-H bonds,and the strong bands at 1387 cm-1 could be assigned to the stretching vibrationof B-O bonds. The thermogravimetric analysis (Fig. 2B) of the VPBA-co- EGDMA polymermonolith indicated that the prepared VPBA-co- EGDMA polymermonolith was thermo-stable,notable mass loss occurred at around 200 °C for both monolithic material. As can be observed,the VPBA-co-EGDMA polymermonolith aged at 80 °C and applied at normal temperatures was stable.

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Fig. 2.(A)FT-IR spectrum of the VPBA-co-EGDMA polymer, (B) TG curve of the VPBA-co-EGDMA polymer, (C) SEM images of the VPBA-co-EGDMA polymermonolith × 160, and (D) SEM images of the VPBA-co-EGDMA polymermonolith × 3000.

The solvent resistance is important for the VPBA-co-EGDMA polymermonolith used for on-line sample pretreatment in HPLC analysis. Water,DMF,methanol,acetonitrile,water/acetic acid (99:1,v/v),acetic acid/methanol (1:9,v/v),water/acetonitrile (7:3, v/v),acetone,ethyl acetate,benzene,toluene,and p-xylene were selected to investigate the solvent resistance of the VPBA-co- EGDMA polymermonolith. After these solvents flowed through the capillary column at a flow rate of 0.2 mL/min for 60 min,no obvious change was observed in the backpressure or morphology. The morphological structure of the VPBA-co-EGDMA polymermonolith was investigated by SEM,and the results are shown in Fig. 2C and 2D. These images show that the VPBA-co-EGDMA polymermonolith was loose and microporous. This morphology is essential to ensure fast mass transport and good permeability, which are advantageous for shortening the analytical time. In addition,the results showed that the VPBA-co-EGDMA polymermonolith had good solvent resistance in a wide variety of solvents.

3.3. Extraction performance 3.3.1. Adsorption characteristics of the VPBA-co-EGDMA polymermonolith

As shown in Table 1,the extraction characteristics of the VPBAco- EGDMA polymermonolith were investigated by comparing the extraction amount of series of organic compounds,including nonpolar polycyclic aromatic hydrocarbons (PAHs) and polar analytes (toluene,benzaldehyde,phenylcarbinol,phenol,and phenylamine). Compounds with π-π conjugate structures are expected to have a strong affinity for the VPBA-co-EGDMA polymermonolith,which is rich in aromatic rings. The adsorption amounts of PAHs increased with an increase in the number of the conjugated double bonds and condensed rings in the analyte. Moreover,the absorption amounts of polar aromatic compounds appeared to be much lower than those of nonpolar species (e.g. phenylamine),further indicating the important role of the π-π stacking interaction. Among the aromatic compounds with different substituents,the adsorption affinity of phenylamine aromatics was much higher than that of the other compounds. Bonding between the nitrogen atoms in guest molecules and the boron atoms in the VPBA moiety of the VPBA-co-EGDMA polymermonolith has been reported to play an important role in the adsorption of small molecules [36]. The experimental results indicated that the presence of hydrogen bonding contributes to the interaction between the polar analytes and the VPBA-co-EGDMA polymer,and hydrophobic interaction was one of the main interactions [37]. As shown in Fig. S1 (Supporting information), the molecular structures of HAAs allow for possible π-π stacking, boron nitrogen bonding,and hydrophobic interactions,therefore, the properties of the VPBA-co-EGDMA polymermonolith make it suitable for enriching HAAs.

Table 1
Enrichment of various compounds with the VPBA-co-EGDMA polymermonolith.
3.3.2. Loading capacity and enrichment factors

To examine the potential adsorption capacity of the VPBA-co- EGDMA polymermonolith,the dynamic binding capacity (DBC) of IQ was determined using the following equation.

in which DBC is the dynamic binding capacity (mg/mL),C0 is the feed concentration of IQ (mg/L),V is the volume of IQ solution pumped into the VPBA-co-EGDMA polymermonolith at 50% breakthrough (mL),VC is the total column volume of the VPBAco- EGDMA polymermonolith,and V0 is the dead volume of the HPLC system. A solution of 1.0 mg/L IQ was pumped through the VPBA-co-EGDMA polymermonolith at a flow rate of 0.20 mL/min at room temperature. The breakthrough curve on the VPBA-co- EGDMA polymermonolith (length: 12.0 cm) was indicated in Fig. 3. From breakthrough curve,a DBC of 0.58 mg/mL and an extraction amount of 5.6 mg was measured for IQ,indicating a high loading capacity on the VPBA-co-EGDMA polymermonolith.

The enrichment factors were calculated by comparing the sensitivity before and after on-line enrichment by the developed method. In comparison with the peak areas of direct injection,a significant enhancement of the peak areas was observed after extraction by the VPBA-co-EGDMA polymermonolith. The enrichment factors were 3746-7414 for the five HAAs examined, indicating the more remarkable pre-concentration ability of the VPBA-co-EGDMA polymermonolith which is significantly greater than that obtained with acrylamide-modified graphene [21].

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Fig. 3.The breakthrough curve of IQ on the VPBA-co-EGDMA polymermonolith. Loading concentration: 1.0 mg/L, Sample flow rate: 0.20 mL/min.
3.3.3. Reproducibility and stability

The column-to-column reproducibility was evaluated by calculating the relative standard deviation (RSD) for extraction of the five HAAs. Satisfactory intra-column (4.9% to 7.7%) and intercolumn (3.0% to 7.8%) RSDs were found. The results proved that the prepared the VPBA-co-EGDMA polymermonolith was quite stable and the synthesis method was reproducible. Moreover,the prepared VPBA-co-EGDMA polymermonolith showed good stability after more than 200 extractions.

3.4. Extraction conditions

In on-line SPME-HPLC-UV,some parameters that might affect the extraction efficiency,including pH of sample solution,flow rate of extraction and desorption,and desorption volume,were investigated to determine the most favourable conditions. Analytes at concentrations of 10.0 g/L each were used,and the extraction amounts of the analytes were used to evaluate the extraction efficiency.

The effect of the pH of the sample solution on the extraction amounts was investigated in the pH range of 4.0-10.0. Fig. 4A shows that the highest extraction amounts were obtained when the loading pH was above pH 9.0. Thus,the pH value was adjusted to 9.0 in the following experiments. The result can be explained by an increase in boronate affinity at higher pH values.

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Fig. 4.Extraction conditions for the VPBA-co-EGDMA polymermonolith. (A) pH of the sample solution, (B) extraction flow rate, (C) desorption volume, and (D) desorption flow rate.

Various extraction flow rates (0.10-0.20 mL/min) were also investigated (Fig. 4B). The experimental results demonstrated that the high flow rate also gave good extraction amounts for the five HAAs. This might be attributed to the fact that the mass transfer of analytes from solution to the VPBA-co-EGDMA polymermonolith is a fast process. A flow rate of 0.20 mL/min was adequate for good extraction efficiency.

Thedesorption volumewas also studied inthe rangeof1.2-2.0 mL (Fig. 4C). The HAAs extracted by the VPBA-co-EGDMA polymermonolith can be almost completely transferred onto the analytical column with 1.80 mL of desorption solvent,and no peak tailing and carry over were observed. The solvent desorption capabilities were also investigated,and the HPLC mobile phase showed good desorption capability. At the same time,using the mobile phase as desorption solvent can simplify the process,and the desorption flow rate was tested from 0.070 to 0.15mL/min. Fig. 4D shows that the most favourable desorption flow rate was 0.10mL/min.

3.5. Application of VPBA-co-EGDMA polymermonolith 3.5.1. Analytical method

The VPBA-co-EGDMA polymermonolith was coupled with HPLC and an on-line SPME-HPLC method was developed for the analysis of the HAAs. Quantitative parameters such as linear equation, linear range,correlation coefficients (R2),and limits of detection (LODs) were evaluated. As shown in Table 2,the linear ranges for IQ,MeIQ,MeIQX,4,8-DiMeIQX,and 4,7,8-TriMeIQX were 0.050- 20,0.050-40,0.0050-50,0.05-10,and 0.050-50 μg/L,respectively, with R2 values ranging from 0.9913 to 0.9993. The LODs (S/ N = 3) were 0.10-0.15 ng/L and the results showed satisfactory inter-day (RSDs from 3.0% to 7.8%) and intra-day (RSDs from 3.9% to 11%) repeatability. These results showed that the proposed method had high sensitivity and good repeatability.

Table 2
Linear range, LOD, repeatability and reproducibility (n = 5).
3.5.2. Sample analysis

To demonstrate the applicability of the on-line SPME-HPLC method for real samples,the proposed method was applied to the determination of trace amounts of HAAs in roast beef,and roast lamb samples. The measured concentrations,RSDs,and the recoveries (n = 5) are presented in Table 3. The results demonstrated that all five of the HAAs could be accurately analysed in real samples. IQ,MeIQ,MeIQX,4,8-DiMeIQX,and MeIQX were detected in all the samples analysed in the concentration rang of 0.235-2.08 ng/g. The accuracy of the on-line SPME-HPLC method was evaluated using a recovery test,in which the samples were spiked with two concentrations(1.6 and 4.8 ng/g) of IQ,MeIQ, MeIQX,4,8-DiMeIQX,and 4,7,8-TriMeIQX. The chromatograms of the 1.6 ng/g spiked samples are shown in Fig. 5(line c). The recoveries for the five HAAs in roast beef and roast lamb samples were 74.3%-116% and 91.3%-119%,respectively. Good repeatability was demonstrated for all the measurements with RSDs from 1.6% to 8.2%,indicating that the on-line VPBA-co-EGDMA polymermonolith-HPLC method is both sensitive and accurate.

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Fig. 5.HPLC chromatograms of HAAs in roast beef, and roast lamb samples (a) a direction injection of the standard solution at 100 μg/L, (b) a sample solution extracted by the VPBA-co-EGDMA polymermonolith, and (c) a 1.6 ng/g spiked sample solution extracted by the VPBA-co-EGDMA polymermonolith.The peaks are: 1. IQ, 2. MeIQ, 3. MeIQX, 4. 4,8-DiMeIQX, and 5. 4,7,8-TriMeIQX.

Table 3
Analysis of HAAs in food samples using the VPBA-co-EGDMA polymermonolith coupled to HPLC (n = 5).
4. Conclusion

In this work,the VPBA-co-EGDMA polymermonoliths were facilely prepared by in situ polymerization using capillaries as moulds. The results indicated that the polymermonoliths could be batch prepared reproducibly. The VPBA-co-EGDMA polymer monolith was porous,chemically stable,had a long lifetime,and showed excellent enrichment factors for pre-concentration of HAAs. An on-line method for trace analysis of HAAs in food samples was developed using VPBA-co-EGDMA polymermonolith extraction coupled to HPLC. Good accuracy and precision were obtained,indicating that the proposed method can be successfully applied to the analysis of HAAs in roast beef and roast lamb samples with good reliability. The on-line method will provide an alternative practical tool for sensitive determination of trace HAAs in complex real samples.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Nos. 21127008,21375155),the Specialized Research Fund for the Doctoral Program of Higher Education (No. 20120171110001),and the Guangdong Provincial Natural Science Foundation of China (No. 2015A030311020).

Appendix A. Supplementary data

Supplementary data associated with this article can be found,in the online version,at http://dx.doi.org/10.1016/j.cclet.2015.10. 023.

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