Development Of Capillary Electrophoresis Instruments For The On-site Determination Of Ions In Environmental Waters

In this paper,two flow-through capillary electrophoresis instruments?FT-CEs?with automatic injection,combined with contactless conductivity detection,have been developed for on-site detection of anions and cations in environmental water samples.The specific content includes:?1?A FT-CE driven by a peristaltic pump was built and applied for the determination of nitrite in water samples.The FT-CE was constructed by two peristaltic pumps,an injection valve,a solenoid valve,a fused silica capillary,a contactless conductivity detector,a high-voltage power supply and other components.Home-made program written by Lab VIEW was used to control the operation of each component and achieve data acquisition.The injection system was investigated by flow injection analysis.The relative standard deviations?RSDs?of ion flow-through time and peak height measured by 30 consecutive injections were 3.49%and 1.43%,respectively,indicating that the system has good repeatability;The FT-CE was applied to the determination of nitrite standards and real water samples.For 0-200?mol/L nitrite ion,the peak height is linear with the concentration,the calibration curve equation was Y=0.00885X-0.00287?R²=0.9923,n=3?,and the limit of detection?LOD?was 6.79?mol/L.?2?A pressure driven FT-CE was built.The difference between this instrument and the peristaltic pump-driven FT-CE was the driven device for the flow-through injection.p L-n L level automatic precision injection by changing the injection time and pressure was achieved by the pressure driven FT-CE.The stability and accuracy of the instrument measurement is improved.?3?By using the pressure driven FT-CE,a method to measure ions in environmental water samples was developed.A new hydrophilic coated 25?m inner diameter capillary was used to suppress the electroosmotic flow.The mixed solution of 400 m M/400 m M Bis-Tris/MOPS and 2 mmol/L 18-crown-6 was used as the background electrolyte?BGE?.By switching the polarity of the high voltage power supply,anions(Cl^-,NO₃^-,NO₂^-,SO₄^2-,F^-and PO₄^3-)and cations(NH₄⁺,K⁺,Na⁺,Ca²⁺and Mg²⁺)could be separated.The internal standard?Li Cl O₄?was online mixed with the sample to correct signal fluctuations caused by temperature or viscosity changes during on-site monitoring.The RSDs of migration time,peak height and peak area were all less than 5%in 350 analysis cycles of about 35 h?both anions and cations were measured as one analysis cycle?.The LODs of inorganic ions ranged from 2.1?mol/L?K⁺?to 6.8?mol/L(PO₄^3-).The instrument was applied to the on-site detection of K⁺,Na⁺,Ca²⁺,Mg²⁺,Cl^-,NO₂^-,SO₄^2-in Xiangsi Lake of Guilin university of Electronic Technology at Huajiang Campus.The obtained results had a good agreement with the results obtained by lab-based ion chromatography method.?4?When using an ultra-narrow capillary for electrophoretic separation,it can not only reduce the heat generation,but also increase the ability of heat dissipation of the separation channel,which can significantly improved the column efficiency and resolution.Fused silica capillaries with internal diameter of 5,10 and 25?m respectively,were used as the separation channel.The effects of large concentration of Na⁺,Cl^-and SO₄^2-,was compared with different size capillaries.It was found that narrower capillary had a better tolerance of high concentration co-existing ion.