Rapid Detection Of Heavy Metal Ions In Water Based On Solid Phase Extraction(SPE) Technology

Copper（Ⅱ）and manganese（Ⅱ）,as two essential trace elements in the human body,participate in many metabolic processes and life activities,and play important biological functions.However,excessive Cu²⁺and Mn²⁺possess strong biological toxicity,which can cause some negative effects on the normal life activities of microorganisms,plants and animals,to some extents.In terms of human body,long-term exposure to Cu²⁺and Mn²⁺can result in irreversible damage to the nervous and digestive systems,and then destroy human body functions.With the rapid development of industry,the contamination of natural water body caused by Cu²⁺and Mn²⁺is continuously growing.The current technologies for the detection of Cu²⁺and Mn²⁺in natural sample primarily relied on large instruments and traditional colorimetric methods.Large instruments possess advantages of high selectivity and sensitivity,but generally suffer from drawbacks such as high-cost and time-consuming,which limit their wide application.On the contrary,colorimetry is known as a simple and inexpensive detection method,but the selectivity and sensitivity are unsatisfactory.Therefore,it is imperative to develop novel methods with facile operation,low cost,high selectivity and sensitivity for Cu²⁺and Mn²⁺detection.In this study,we developed two novel detection methods for Cu²⁺and Mn²⁺,respectively,based on SPE（solid phase extraction）-assisted optical method.The specific methods are as follows:（1）A SPE-based method for detecting Cu²⁺in water was established.The SPE column was firstly fabricated by fill of sulfonated polystyrene-divinylbenzene copolymer（PS-DVB）microspheres with relatively large particle size.Secondly,the oxalic acid was demonstrated capable of specific elution of Cu²⁺from metal cations complex solution,and the elution condition was optimized.Thirdly,a paper-based analytical device（μPAD）for Cu²⁺was established using PVB（polyvinyl butyral）-immobilized 1-（2-pyridylazo）-2-naphthol（PAN）as the indictor.The color difference ofμPAD before and after detection was digitized by scanner and was employed to determine the Cu²⁺concentration in water samples.The experimental results demonstrated the as-fabricated SPE was capable of specific separation of Cu²⁺from metal cation complex.By collaborating with PVB-PAN-basedμPAD,the limit of detection（LOD）of Cu²⁺was achieve 0.340μM,which is much lower than the Cu²⁺concentration allowed for Chinese standard of drinking water（GB 5749-2006）.In real sample experiments,the recovery of Cu²⁺was determined as 96.780～99.232%,demonstrating the feasibility of this method.（2）A method for detecting Mn²⁺in water was established.Mn²⁺extraction system was consisted of SPE column and citric acid eluent.By optimizing elution condition,SPE was demonstrated capable of effective separation of Mn²⁺from other interfering ions.A europium(Eu³⁺)-based fluorescent probe was synthesized using 2,6-pyridinedicarboxylic acid（PDCA）and 2-thenoyltrifluoroacetone（TTA）as co-ligands,and were employed to realized quantitative detection of Mn²⁺due to excellent relationship between fluorescent intensity of Eu³⁺fluorescent probe and Mn²⁺concentration.The limit of detection（LOD）of Mn²⁺was determined as low as 0.200μM.In real sample experiments,negligible difference was observed between results of Mn²⁺concentration determined by this method and flame atomic absorption spectrometry（FAAS）,indicating excellent capability of this method in Mn²⁺detection in water.The as-fabricated SPE-column can be reused and enable selective separation of Cu²⁺or Mn²⁺by regulating eluent.By cooperation of suitable optical sensors,namely PAN-basedμPAD or Eu³⁺-based fluorescent probe,the quantitative detection of Cu²⁺or Mn²⁺can rapidly achieved through changes of color or fluorescence intensity,respectively.These two methods have been demonstrated with advantages including simple operation,low cost,high selectivity and sensitivity.