A Highly Portable Smartphone-Based Capillary Electrophoresis with Capacitively Coupled Contactless Conductivity Detection

Abstract

Work has rarely been reported on a highly portable smartphone-based capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C⁴D). Herein, a highly portable phone-based CE (130 mm × 190 × 70 mm, 1.4 kg) with C⁴D and Bluetooth communication, as well as user-interface software, was developed for portable analysis. To demonstrate the device, six metal ions were selected as model analytes for verification and successfully applied to the detection of ions in tap water. The analytical performance highlighted that the runs and data analysis of the CE-C⁴D device could be controlled via the user interface based on smartphones. Furthermore, the experiments showed that (i) the linear ranges of six metal ions were between 6 and 1500 μmol/L with a correlation coefficient of more than 0.9934; (ii) the limit of detection (LOD) values were within 1.84-4.33 μmol/L; (iii) the intra-day deviations of migration time and peak area were 2.40-5.24% and 0.75-2.82% (n = 5), respectively. Although the LOD is not the most optimal among current portable devices, the results still indicated the satisfactory analytical performance and potential of the developed device, software, and method for portable separation and quantitation of analytes from various fields.

Keywords: capacitively coupled contactless conductivity detection; capillary electrophoresis; metal ions; portability; smartphone.

Figure 1

Schematic diagram of the portable smartphone-based CE-C⁴D with three parts of CE separation and cleaning (A), the online C⁴D (B), and the smartphone (C). Panel A: (a) capillary, (b) sample vial, (c) anode BGE vial, (d) cathode BGE vial, (e) micro diaphragm pump, (f) high-voltage power supply, (g) C⁴D-sensing section, and (h) control and signal-processing module.

Figure 2

Real photograph of the portable smartphone-based CE-C⁴D device, including top view (A), capillary winding diagram (B), sensor board diagram (C), T-tube diagram (D), and internal diagram (E). Herein, (a) capillary, (b) sample vial, (c) anode BGE vial, (d) cathode BGE vial, (e) micro diaphragm pump, (f) high-voltage power supply, (g) sensor board, (h) main board, (i) potentiometers for baseline adjustment and amplification, (j) T-tube, (k) lithium battery, and (m) metal shell.

Figure 3

User interface of conductivity detection mobile software for controlling of developed CE-C⁴D device of Bluetooth scanning (A), CE condition setting (B), CE run (C), and data processing (D).

Figure 4

The developed device (A) and the core steps, such as Bluetooth scanning (B), Bluetooth connecting (C), controlling the power supply with the smartphone with a 15 kV output (D) of the CE run. Herein, the YD1940A high-voltage digital voltmeter was used to verify the high-voltage output set on the smartphone.

Figure 5

Electrophoretograms for BGE with six single ions and their mixture. a—100 μmol/L K⁺, b—100 μmol/L Ca²⁺, c—100 μmol/L Na⁺, d—100 μmol/L Mg²⁺, e—100 μmol/L Mn²⁺, f—200 μmol/L Zn²⁺, g—mixture. BGE: 25 mmol/L Lac-β-Ala (pH 3.6). Capillary: length of 60 cm (effective length of 50 cm), o.d. of 365 μm and i.d. of 75 μm. Separation voltage: 15 kV. Injection time: 3 s. Excitation source: peak–peak voltage of 20 V and frequency of 40 kHz. DC signal magnification: 100.

Figure 6

Electrophoretograms for BGE with diluted tap water via the portable smartphone-based CE-C⁴D device, including the baseline fitting (A), and peak area calculation (B). The dark gray line, red line, and gray line represent the electrophoretic curve, the fitted baseline, and the reconstructed Gaussian peak, respectively. BGE: 25 mmol/L Lac-β-Ala (pH 3.6). Capillary: length of 60 cm (effective length of 50 cm), o.d. of 365 μm and i.d. of 75 μm. Separation voltage: 15 kV. Injection time: 3 s. Excitation source: peak–peak voltage of 20 V and frequency of 40 kHz. DC signal magnification: 100.