Li Lin, Ren Dou-Dou, Zhang Peng-Yu, Song Yun-Peng, Li Tang-Xiu, Gao Ming-Hui, Xu Jia-Nan, Zhou Lei, Zeng Zhi-Cong, Pu Qiaosheng
State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China.
Anal Chem. 2024 Jun 25;96(25):10356-10364. doi: 10.1021/acs.analchem.4c01367. Epub 2024 Jun 12.
Capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-CD) has proven to be an efficient technique for the separation and detection of charged inorganic, organic, and biochemical analytes. It offers several advantages, including cost-effectiveness, nanoliter injection volume, short analysis time, good separation efficiency, suitability for miniaturization, and portability. However, the routine determination of common inorganic cations (NH, K, Na, Ca, Mg, and Li) and inorganic anions (F, Cl, Br, NO, NO, PO, and SO) in water quality monitoring typically exhibits limits of detection of about 0.3-1 μM without preconcentration. This sensitivity often proves insufficient for the applications of CE-CD in trace analysis situations. Here, we explore methods to push the detection limits of CE-CD through a comprehensive consideration of signal and noise sources. In particular, we (i) studied the model of CD and its guiding roles in CD and CE-CD, (ii) optimized the bandwidth and noise performance of the current-to-voltage (-) converter, and (iii) reduced the noise level due to the strong background signal of the background electrolyte by adaptive differential detection. We characterized the system with Li; the 3-fold signal-to-noise (S/N) detection limit for Li was determined at 20 nM, with a linear range spanning from 60 nM to 1.6 mM. Moreover, the optimized CE-CD method was applied to the analysis of common mixed inorganic cations (K, Na, Ca, Mg, and Li), anions (F, Cl, Br, NO, NO, PO, and SO), toxic halides (BrO) and heavy metal ions (Pb, Cd, Cr, Co, Ni, Zn, and Cu) at trace concentrations of 200 nM. All electropherograms showed good S/N ratios, thus proving its applicability and accuracy. Our results have shown that the developed CE-CD method is feasible for trace ion analysis in water quality control.
采用电容耦合非接触式电导检测的毛细管电泳(CE-CD)已被证明是一种分离和检测带电无机、有机及生化分析物的有效技术。它具有若干优点,包括成本效益高、纳升进样体积、分析时间短、分离效率高、适合小型化以及便携性。然而,在水质监测中常规测定常见无机阳离子(NH₄⁺、K⁺、Na⁺、Ca²⁺、Mg²⁺和Li⁺)和无机阴离子(F⁻、Cl⁻、Br⁻、NO₂⁻、NO₃⁻、PO₄³⁻和SO₄²⁻)时,若不进行预浓缩,检测限通常约为0.3 - 1 μM。这种灵敏度在CE-CD用于痕量分析的情况下往往被证明是不够的。在此,我们通过全面考虑信号和噪声源来探索降低CE-CD检测限的方法。具体而言,我们(i)研究了电导检测模型及其在电导检测和CE-CD中的指导作用,(ii)优化了电流 - 电压(I-V)转换器的带宽和噪声性能,以及(iii)通过自适应差分检测降低了背景电解质强背景信号导致的噪声水平。我们用Li⁺对该系统进行了表征;Li⁺的3倍信噪比(S/N)检测限确定为20 nM,线性范围为60 nM至1.6 mM。此外,优化后的CE-CD方法被应用于分析痕量浓度为200 nM的常见混合无机阳离子(K⁺、Na⁺、Ca²⁺、Mg²⁺和Li⁺)、阴离子(F⁻、Cl⁻、Br⁻、NO₂⁻、NO₃⁻、PO₄³⁻和SO₄²⁻)、有毒卤化物(BrO₃⁻)和重金属离子(Pb²⁺、Cd²⁺、Cr³⁺、Co²⁺、Ni²⁺、Zn²⁺和Cu²⁺)。所有电泳图均显示出良好的信噪比,从而证明了其适用性和准确性。我们的结果表明,所开发的CE-CD方法在水质控制中的痕量离子分析方面是可行的。