Development of a High-Performance Imaging-Aided Extractive Electrospray Ionization Sprayer

Extractive electrospray ionization (EESI) source has become a hot research topic in recent years owing to its many advantages, such as no need of complicated sample pretreatment, ease of integration and miniaturization, the ability of on-site analysis, etc. Sprayer hole is one of the most important parameters affecting EESI source's performance. However, since the geometric scale of sprayer hole is very small, the performance of EESI source is difficult to be optimized using conventional methods. In this study, a high-performance optical imaging method was developed to improve the spray efficiency of EESI source, which is very useful to detect and evaluate the coordinates of the sprayer holes geometric contours. Through comparing the diameter and roundness error of the sprayer holes made by the traditional and our new approaches, the optimized instrument parameters were obtained and examined. Under the optimized conditions using the EESI source manufactured through the new technology, the detection limit of methamphetamine was remarkably improved from 0.101 μg/L to 0.041 7 μg/L, and the RSD decreased to 0.6%-4.2% from 0.9%-5.8%. The experimental results are consistent with that obtained using the image measurement method. For the EESI source manufactured using the new technology, more compounds of wide interest, such as codeine, heroin, ketamine, benzedrine, caffeine, ephedrine, methamphetamine, diazepam, pentobarbital, and estazolam in urine, were used in test experiments for five consecutive days. The maximum RSD for these samples was less than 5.2%. The results show that the new technology makes the EESI source much more stable and sensitive, and more suitable for the application of EESI sources in commercial settings. The imaging aided method has advantages of simple operation, which can reduce time and cost for the development of a high performance EESI source.