正峰间接电容检测在离子色谱中的应用

Positive Peak Indirect Capacitance Detection in Ion Chromatography

在离子色谱(IC)中,由于氢离子(H+)的等效电导率最高,采用无机酸洗脱液(如HNO 3)进行阳离子分析时,间接电导检测出现负峰.用HNO 3洗脱液进行碱离子分析时,在非接触式电容检测器(CCD)上观察到了不受抑制的异常正峰,发现CCD响应曲线和电解液浓度曲线存在最大值.在低浓度下,当电解液浓度超过某特定临界值(CCV)时(例如一些电导率大于~1.2 mS/cm,与洗脱液性质无关),电容信号随电解液浓度单调增加,与自猝灭荧光很相似,随着电解液浓度的增加,电容信号减小.当流动池内径增大时,CCV向低值方向移动.

It is known that negative peaks under indirect conductometric detection in ion chromatography(IC)are observed when inorganic acid eluent(e.g.HNO 3 or methanesulphic acid,MSA)is used for cation analysis since hydronium ion(H+)has the highest equivalent conductivity of all cations.While HNO 3 eluent is used for alkali cation analysis,unusual positive peaks on a contactless capacitance detector(CCD)(essentially as a non-galvanic conductance detector)without any suppression are observed.It is found that there is maximal value for the plot of CCD response and the electrolyte concentration.At low concentration,the measured capacitance monotonically increases with the electrolyte concentration,when the electrolyte concentration is over than a certain critic value(CCV)(e.g.the specific conductivity is higher than^1.2 mS/cm,regardless of the nature of eluents).Much like fluorescence that is self-quenched,the capacitance signal decreases with the increase of electrolyte concentration.The CCV shifts towards lower value when the inner diameter of the flow cell increases.