Flow-batch system based on Quartz Crystal Microbalance (QCM) sensor for the determination or arsenic in water

This project presents a lab-made instrument to measure the amount of arsenic present in water. This natural pollutant compromises the potability of water for humans, with a maximum limit of 10 ug L-1 in drinking water. Its presence in Argentina underground water is extended along a large area involving several provinces. The system uses flow-batch technology to handle the samples. This technology has several advantages over traditional methods: it uses small samples reducing the amount of reagents and residues left after the measurements, it can be systematized as the control of the procedure is made with a computing device, it can be implemented in the lab with low-cost elements, and provides high precision in the results when properly configured. Flow-batch systems are increasingly being used in analytical chemistry. In the case of this instrument, the flow-batch system is used to process the sample in order to isolate the arsenic present in the water. The measurement is indirect as it is the arsine present in the gaseous output what is measured through a QCM microbalance. QCM is a special quartz crystal that varies its resonanting frequency, or what is the same its admittance equivalent according to the dopping of its surface. As the gaseous arsine flows into the chamber the surface of the QCM is dopped with it and in this way its admittance is changed. The whole control of the flow-batch system and the gaseous flow is handled with a microcontroller platform based on the ESP-32 device while the admittance measurement is done with a commercial FPGA instrument. The system was built in the lab using several commercial elements like the solenoid valves or stepper motors. Beaker, reaction and measurement chambers were built in the lab, like the PCB and the assembly of the electronics together with different pieces specially design and built with a 3D printer for the peristaltic pump and several other elements.

本课题展示了一种实验室自制仪器，用于测量水中砷的含量。该天然污染物损害了人类饮用水的适口性，饮用水中砷的最大限量规定为10微克每升。在阿根廷地下水中，其分布范围广泛，涉及多个省份。该系统采用流批技术处理样本。相较于传统方法，该技术具有多方面的优势：它使用少量样本，减少了测量后剩余的试剂和残留物，可以系统化控制，因为过程控制由计算设备完成，可以在实验室中利用低成本元件实现，并且在正确配置的情况下提供高精度结果。流批系统在分析化学中日益得到应用。在本仪器中，流批系统用于处理样本，以分离水中的砷。测量是间接的，因为是通过测量气态输出中的胂来实现的，该气态输出通过石英晶体微天平进行测量。石英晶体微天平是一种特殊的石英晶体，其共振频率或与其表面掺杂相对应的导纳会发生变化。当气态胂流入腔室时，石英晶体微天平的表面被掺杂，从而改变了其导纳。整个流批系统和气态流量的控制由基于ESP-32设备的微控制器平台完成，而导纳测量则由一款商业化的FPGA仪器完成。该系统在实验室中构建，使用了多个商用元件，如电磁阀或步进电机。烧杯、反应和测量腔室均在实验室中制作，包括PCB和电子组件的组装，以及使用3D打印机特别设计和构建的蠕动泵和其他几个元件。