Research On Synchronous Determination Of Anions And Cations Based On Capacitively Coupled Contactless Conductivity Detection In Microchip Electrophoresis

Concurrent determination of inorganic cations and anions is crucial in many fields,such as soil nutrient detection,farmland non-point source pollution monitoring,water and fertilizer integrated irrigation monitoring,air particulate matter(PM)monitoring,drug preparation testing and so on.The newly arisen microchip electrophoresis based on capacitively coupled contactless conductivity detection(ME-C4D)technology has many advantages such as rapid multi-ion synchronous detection,low sample and reagent consumption and low detection cost,etc.However,due to the limitations of the existing microchip electrophoresis technology,it cannot be widely applied to the simultaneous detection of anions and cations.In addition,there are no mature portable instrument products suitable for on-site testing in the field at home and abroad,making this technology which has great application potential not yet widely available.In view of this,this article focuses on the development of a ME-C4D technology that is capable of concurrent and rapid detection of a variety of anions and cations,and carries on technology integration and weight-lightening research to develop a portable ion velocity meter.In this paper,with reference to the concurrent determination of cations and anions in capillary electrophoresis,combined with the relevant characteristics of the ME-C4D technology,we studied deeply the theoretical principles of the microchip electrophoresis and the capacitively coupled contactless conductive detection,and proposed two methods based on the bent and Y-type microchip for the concurrent determination of cations and anions.The related ME-C4D system was developed and the feasibility of the two detection methods was verified experimentally.In this paper,the method of ME-C4D technology for the synchronous detection of cations and anions was deeply studied.At first,the electroosmotic flow-driven capillary electrophoresis was transplanted to microchip electrophoresis.Experiments show that this method is only applicable to the detection of anions and cations with large difference in charge-to-mass ratio.We proposed a scheme for synchronous detection of cations and anions based on bent electrophoretic microchip channels.The CTAB reagent was used to suppress electroosmotic flow in electrophoretic microchannels.Our self-developed program-controlled high-voltage generation module enabled the anions and cations to migrate serially in the electrophoretic microchannels at different speeds in the same direction,and thus to achieve the simultaneous detection of anions and cations in the same microchip electrophoresis channel.In view of the back-migration problem of the cations existing in this scheme,we proposed a new detection scheme based on the Y-type electrophoresis micro-channels so that the anions and cations can enter different micro-channel branches after passing through the detection position.And the method can completely eliminate the phenomenon of "back migration" of ions.Experiments show that both schemes can perform synchronous serial detection of K+,Na+,Li+,Cl-,F-and PO43-in 140 seconds.Aimed at the problem that the current electrophoresis microfluidic chip has a complex manufacturing process and relies on expensive microfabrication equipment,this paper proposed a detachable microelectrophoresis chip that is extremely simple to manufacture and is convenient for large-scale production.And a C4D circuit was developed to constitute a complete new ME-C4D system.Through the in-depth analysis of each module of the C4D system and optimization of electrophoretic detection parameters,the successful detection of soil nutrients and heavy metal ions was completed.On this basis,the ME-C4D system was integrated and weight-lightened,and a prototype of a portable ion velocity meter that can be used in the field was developed.The research work in this paper solves the defects of the current microchip electrophoresis technology for the synchronous detection of cations and anions,realizes simultaneous and rapid detection of multiple types of anions and cations in the same micro-electrophoresis channel,and develops a portable ion velocity measurement instrument prototype suitable for on-site detection in the field.It is an important impetus to the practical application of ME-C4D technology and large-scale commercial applications.