| Objectives For conventional off- line solid-phase extraction(SPE), there are difficulties in reusability and automation. In this work, an ion-exchange poly(2-(acryloyloxy)ethyl trimethyl ammonium chloride-co-ethylene glycol dimethacrylate)(poly(DAC-co-EDMA)) monolithic column was fabricated and developed as a reusable sorbent for on-line SPE followed by liquid chromatography-tandem mass spectrometry(LC-MS/MS) for determination of salicylic acid in pork, chicken liver, egg and milk.Methods 1 The ion-exchange monolithic column was prepared in a stainless column(10 mm × 2.1 mm i.d.) via in-situ copolymerization of 2-(acryloyloxy)ethyl trimethyl ammonium chloride(DAC) as monomer and ethylene dimethacrylate(EDMA) as crosslinking agent. The ratios of porogens(polyethylene glycol 400: n-propanol= 5/1-1/5, V/V), the amount of DAC(18-46 mg) and the reaction time(12-24 h) were investigated. The prepared columns were characterized by scanning electron microscope and nitrogen adsorption-desorption. 2 On-line SPE was performed on the synthesized poly(DAC-coEDMA) monolith and the parameters of on- line SPE were optimized such as the loading solution(0.5% formic acid solution and water), the concentration of formic acid(0.5%-2%) and the flow rate(0.2-0.5 m L/min) of the eluting solution. The composition of the mobile phase containing 5 mmol/L NH4 OAc solution and acetonitrile(Me CN)(60/40, 80/20, 95/5, V/V) was optimized for LC-MS/MS separation. 3 Finally, specificity, limit of detection(LO D), limit of quantification(LOQ), accuracy and recovery of the proposed method were investigated. The reusability and reproducibility of the poly(DAC-coEDMA) monolithic extractors were evaluated by calculating the the relative standard deviations(RSDs) of the extracted peak area of salicylic acid.Results 1 On the basis of the results, the monolithic column was prepared with the mixture of polyethylene glycol 400 and n-propanol(1/2, V/V) and 32 mg DAC for 20 h. The scanning electron microscope image displayed the porous and uniform morphology of the monolith. The surface area was found to be 326.11 m2/g. 2 On- line SPE was performed on the synthesized monolithic column using water as loading solution. The eluting of salicylic acid was achieved with 2% formic acid- methyl alcohol(2/98, V/V) solution at the flow rate of 0.3 m L/min. The extracted analytes were subsequently eluted into a C18 analytical column for LC-MS/MS using a mixture of 5 mmol/L NH4OAc- Me CN(95/5, V/V) as the mobile phase. 3 The proposed method was linear over the range of 2-100 μg/kg salicylic acid. The LOD was 5 μg/kg and the LOQ was 10 μg/kg. The recovery of salicylic acid in measured samples ranged from 85.2% to 98.4% with the relative standard deviations of less than 7.2%. The reproducibility(RSD) of the first injection, the 200 t h injection and the 500 t h injection was 5.8%. The intra-batch and interbatch RSDs were 6.6% and 11.2%, respectively.Conclusions Compared with the results have been reported, it has been demonstrated that the proposed method can be used for routine determination of salicylic acid in pork, chicken liver, egg and milk with wide linear range, acceptable recovery and low detection limit. Moreover, the novel sorbent of ion-exchange monolithic column has the remarkable advantages of easy preparation, high extraction efficiency and satisfactory reusability. |
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