On-capillary Multi-detection Combined Detectors Fabricated By 3D Printing

Capillary electrophoresis(CE)is a high efficiency separation technique for the determination of pollutants in environment.Common on-capillary detection methods of CE include photometry(PD),fluorimetry(FD),and contactless conductometry(C~4D).When a single method is used for direct detection,the applicable range of analytes is limited.The combination of multiple detection methods can simultaneously detect multiple types of analytes.However,the process of fabrication of a combined detector by traditional machining method is complicated.It is also difficult to optimize the geometry of a combined detector.The rapid development of 3D printing technology provides a new approach for the manufacture of analytical instruments.In this paper,3D printing technology was used to build on-capillary combined detectors for CE.(1)A two-in-one 3D printing detector combing of C~4D and PD for CE,was fabricated with the multi-material 3D printing technology.C~4D Faraday Shield was made of conductive polylactic acid(PLA).Non-conductive PLA was used for printing insulating layer.Two metal tube electrodes were embedded into the non-conductive PLA material by"print-pause-print"method.A novel collimator(0.1 mm wide),consisting of two partially aligned pinholes(0.5 mm wide of each),was printed by conductive material to collimate the light-emitting diode beam.The detector was used for 50μm id capillary PD detection,and the effective optical path was 25μm.Cations complexed with 4-(2-Pyridylazo)resorcinolwas(PAR)were electrophoretic separated with a 25μm id capillary.The detection limits(LOD)of Co(II)-PAR,Cu(II)-PAR and Zn-(II)PAR in PD were 1.3,0.9 and 1.7μM.The LODs of K~+,Na~+,Co(II)-PAR and Zn(II)-PAR in C~4D were 1.2,1.4,21 and 2.6μM.(2)A three-in-one detector combing C~4D,PD and FD was first time fabricated by using SLA and FDM printing.To make the slit for PD detection,two 0.05 mm deep grooves were made on the surface of two print modules using accurate SLA printing,and then the two grooves were then sealed together to build a 0.1 mm wide slit.The C~4D electrode and Faraday shielding were built by casting a low melting point metal into printed chambers.Conductive composite PLA material was also used to build the outside Faraday shielding layers for C~4D.A 1.6 mm circular hole was in the middle of electrodes for laser-induced fluorescence detection.In PD detection,the effective path length of 50μm id capillary was43.2μm,and the stray light was 9.5%.The optimal excitation frequency was 153.8 k Hz in C~4D.The LOD of fluorescein in FD was 10 n M.(3)Electrophoresis analysis of mixed ions were carried out by using a self-made CE device coupled with the 3D printing three-in-one detector.1)Six amino acids labeled with inorganic ions fluorescein isothiocyanate(FITC)along with K~+,Na~+,Li~+were separated.The LODs of Lysine in C~4D,PD and FD were 4.8μM,3.7μM and 15 n M,respectively.The migration time difference of different detection methods for the same signal peak was less than 0.6 s.2)Mixture of typical anions and rhodamine compounds was separated and detected under acidic and alkaline conditions respectively.Under acidic condition(p H=3.3),the LODs of phthalates acid C~4D and PD detection were 5.3μM and 40.1μM,respectively,and the LODs of Rhodamine 123 PD and FD were 6.2μM and 46.4 n M,respectively.3)Separation of glyphosate,glufosinate and aminomethylphosphoric acid were carried out.The LODs of glyphosate,glufosinate and aminomethyl phosphate by FD method were 5.0μM,0.8μM and 0.8μM,the calibration range is 5μM to 500μM.