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.