氧化石墨烯功能化三聚氰胺-甲醛气凝胶涂层固相微萃取管的制备及其应用

Preparation and application of graphene oxide functionalized melamine-formaldehyde aerogel coated solid-phase microextraction tube

因具有良好的萃取性能,有机气凝胶已被应用于样品前处理领域,为了进一步改善其对多环芳烃类污染物的萃取能力,利用氧化石墨烯对三聚氰胺-甲醛气凝胶进行改性,制备了一种氧化石墨烯功能化三聚氰胺-甲醛气凝胶,将其作为萃取涂层涂覆到不锈钢丝表面,通过扫描电镜和X射线光电子能谱对萃取涂层进行表征,结果表明氧化石墨烯并未破坏气凝胶的三维网络多孔结构。将4根气凝胶涂覆的不锈钢丝装进一根长度30 cm、内径0.75 mm的聚醚醚酮管内,制备了一种新型的纤维填充型固相微萃取管。将萃取管与高效液相色谱联用,构建管内固相微萃取-液相色谱在线富集分析系统。以8种多环芳烃(萘(Nap)、苊烯(Acy)、苊(Ace)、芴(Flu)、菲(Phe)、蒽(Ant)、荧蒽(Fla)和芘(Pyr))作为模型分析物,评价了萃取管的萃取性能,考察了氧化石墨烯对气凝胶萃取性能的改善,结果表明萃取效率被提升至最高2.5倍。详细考察了样品体积、样品流速、样品中有机溶剂浓度以及脱附时间对于萃取效率的影响,并建立了管内固相微萃取-液相色谱在线分析方法。该法对8种多环芳烃分析物的检出限为0.001~0.005μg/L,萘、苊烯、苊、芴的线性范围为0.017~20.0μg/L,菲、蒽的线性范围为0.010~20.0μg/L,荧蒽和芘的线性范围为0.003~15.0μg/L,精密度良好(日内重复性RSD≤4.8%,日间重复性RSD≤8.6%)。研究所发展的分析方法比已报道的某些分析方法具有更好的灵敏度、更宽的线性范围和更短的分析时间,并具有在线富集和在线分析的独特优点。将该分析方法应用于常见饮用水(包括瓶装矿泉水和饮水机的直饮水)中多环芳烃的分析检测,加标回收率试验结果(76.3%~132.8%)表明该分析方法能够高灵敏、快速、准确地检测饮用水中痕量多环芳烃污染物。经过稳定性考察,发现研究所制备的固相微萃取管在实验过程中表现出良好的使用寿命和化学稳定性。

Many solid-phase microextraction(SPME)sorbents have been developed from aerogels because of their low densities,large surface areas,and high porosities. Melamine-formaldehyde(MF)aerogel,made from melamine and formaldehyde by a sol-gel reaction,is one of the typical organic aerogels. MF aerogel has better mechanical strength,chemical stability and extraction performance than inorganic aerogels. The performance of the aerogel is limited in some fields,while composite aerogels can meet different requirements such as good mechanical strength and strong adsorption performance. Graphene oxide(GO)is a two-dimensional nanomaterial composed of a single layer of carbon atoms and provides π-π interaction by a large π-electron. In addition,the oxygen-containing groups at the edge of the lamellar structure improve the hydrophilicity of the material and can interact with various compounds. To improve the extraction performance of MF aerogel for polycyclic aromatic hydrocarbons(PAHs),GO/MF aerogels were prepared by functionalizing MF aerogel with GO. In this study, 1. 261 2g of melamine and80mg of sodium carbonate were dissolved in30mL of water,and the mixture was heated to80℃ under stirring. Then, 2. 8mL formaldehyde solution(37%)was slowly added,and a clear solution was obtained gradually. Next, 50mg of GO powder was ultrasonically dispersed in10. 0mL of water and evenly mixed with the above solution. After adjusting the pH to1. 5,the sol-gel process was performed for48h,then the gel was aged at room temperature for24h. The gel was then soaked in ethanol,acetone,and cyclohexane in turn to replace the solvent. Finally,the GO/MF aerogel was obtained by freeze-drying for24h. The GO/MF aerogel was characterized by scanning electron microscopy(SEM)and X-ray photoelectric spectroscopy(XPS),confirming that GO was successfully introduced into MF aerogel,while retaining its three-dimensional network and porous structure. GO/MF aerogel was coated onto the surface of a stainless steel wire to be used as sorbent. Four such wires were placed into a polyetheretherketone(PEEK)tube(0. 75mm i. d., 30cm length)for intube(IT)SPME. The tube was combined with a high-performance liquid chromatography(HPLC)unit to construct an IT-SPME-HPLC online system. When the six-way valve was in the Load state,sample solution achieved online enrichment with analytes while it flowed through the extraction tube. After extraction,the valve was turned to the Inject state,and the analytes were eluted into the chromatographic column by the mobile phase at a flow rate of1. 0mL/min for separation and detection with the detector. Under the same extraction conditions(sampling volume= 30mL,sampling rate= 1. 00mL/min,and concentration of polycyclic aromatic hydrocarbons(PAHs,viz. naphthalene(Nap),acenaphthylene(Acy),acenaphthene(Ace),fluorine(Flu),phenanthrene(Phe),anthracene(Ant),fluoranthene(Fla)and pyrene(Pyr))=5. 00 μg/L),GO/MF aerogel-based tube was compared with that of MF aerogel-based tube. GO enhanced the enrichment efficiency of MF aerogel towards PAHs from1. 1to2. 5times,due to the increased number of adsorption sites and enhanced π-π interaction with PAHs. IT-SPME was affected by the sampling volume,sampling rate,concentration of organic solvent in sample,desorption solvent,desorption rate,and desorption time. To obtain accurate results,the main extraction and desorption conditions(sampling volume,sampling rate,organic solvent concentration,desorption time)were investigated carefully. As the sampling volume in the extraction tube was increased,the extraction efficiency was found to increase gradually until saturation. In this study,the extraction efficiency was investigated for sampling volumes ranging from30to80mL,and70mL was selected as a suitable sampling volume to achieve satisfactory extraction efficiency. The sampling rate affects not only the extraction efficiency,but also the extraction time. When the sample flows through the extraction tube at a low rate,it requires a long test time. Although the increase in sampling rate reduces the extraction time,it often decreases extraction efficiency. In addition,large sampling rate leads to high pressure in the tube,which in turn reduces the service life of the tube. Therefore,the effect of sampling rate(1. 25-2. 50mL/min)on extraction efficiency was investigated,and good extraction efficiency and short test time were achieved when the sampling rate was2mL/min. High hydrophobic PAHs have poor solubility in water. An appropriate amount of organic solvent in the sample solution can improve the solubility of PAHs to obtain accurate analytical results. However,the extraction efficiency was affected by the added organic solvent. Thus,the effect of volume fraction of methanol(0, 0. 5%, 1%, 2%, 3%,and5%,v/v)on the extraction efficiency was investigated. The sample solution without methanol afforded better extraction efficiency and satisfactory repeatability. After online extraction,the desorption directly affects the desorption efficiency. The peak areas of the eight PAHs were investigated with different desorption times(0. 2, 0. 4, 0. 6,0. 8, 1. 0,and2. 0min),and a desorption time of2. 0min was required to fully desorb all analytes and reduce their residuals. The IT-SPME-HPLC-DAD method was established under the optimized conditions,and the limits of detection(LODs),linear equations,linear ranges,and correlation coefficients were obtained. The LODs of the eight PAHs were in the range of0. 001-0. 005 μg/L,the quantitative ranges of the analytes were0. 003-15. 0 μg/L for Fla and Pyr,0. 010-20. 0 μg/L for Phe and Ant,and0. 017-20. 0 μg/L for Nap,Acy,Ace and Flu,the enrichment factors were in the range of2 029-2 875,and the analytical precision was satisfactory(intra-day RSD%≤4. 8%,and inter-day RSD≤8. 6%). Compared with some reported methods,the method reported herein provided higher sensitivity,wider linear range,and shorter test time. This method was applied to the detection of PAHs in common drinking water,including bottled mineral water and water from drinking fountain. The satisfactory recovery( 76. 3%-132. 8%)obtained proves that the method is suitable for the determination of trace PAHs in real water samples,with high sensitivity,rapid testing,online detection,and good accuracy. The extraction tube also exhibited satisfactory durability and chemical stability.