[Determination of two quaternary ammonium salts in disinfector by portable capillary electrophoresis device based on smartphone]

The existing miniature capillary electrophoresis (CE) devices use a tablet or a computer for data processing and analysis, which hinders their portability. In order to solve this problem, a smartphone-based CE device was proposed, which allowed for real portable quantitative analysis. The device integrated the functions of capacitively coupled contactless conductivity detection (C4D) and Bluetooth communication. Furthermore, a Kotlin language-based application with a user-friendly interface was developed. The application could not only control the electrophoresis run in the CE device but also receive the data from the C4D detector in real time, display the electrophoretogram, and process the data. The peak areas could be calculated automatically on the smartphone, and the migration time could be obtained. The size of the developed device was 20 cm×20 cm×15 cm, and its weight was 2 kg. Quaternary ammonium salts (QAs) in disinfectors (dodecyl dimethyl benzyl ammonium bromide (DDBAB) and dodecyl trimethyl ammonium bromide (DTAB)) were used as the analytes to verify the performance of the developed device. The experimental data showed that the linear ranges of DDBAB and DTAB were from 20 to 1000 and from 30 to 1000 μmol/L, respectively. The correlation coefficients (R2) of DDBAB and DTAB were 0.9995 and 0.9989, respectively, indicating good linearity between the peak area and concentration. The limits of detection (LODs) of DDBAB and DTAB were 10 and 13 μmol/L, respectively. The intra-day relative standard deviations (RSDs, n=3) of DDBAB and DTAB were 1.9% and 2.7% respectively, revealing good repeatability. In addition, a mixture of DDBAB and DTAB was tested. Two QAs were separated within 8 min, showing good selectivity. Finally, QAs in a bromo geramine disinfector used in the field were tested to further validate the performance of the designed device. The recoveries of DDBAB and DTAB were 100.5%-101.5% and 96.2%-99.3%, respectively, indicating good accuracy. The developed device has the advantages of good linearity, low LOD, good repeatability, high accuracy, and real portability, and it can be used for the quantitative detection of QAs in disinfectors.