Definition
Automatic ultrapure water is a water purification system that integrates pretreatment, reverse osmosis, ion exchange, ultrafiltration, ultraviolet oxidation and terminal filtration technologies. It continuously and stably prepares ultrapure water with a resistivity of 18.2 trillion ohms per centimeter and a total organic carbon content of less than 5 micrograms per liter through automatic control programs, meeting the high standards of water quality in various precision analysis experiments.
Principle
Systems typically work in tandem with multi-stage purification modules. The raw water first passes through the pretreatment unit to remove suspended particles and residual chlorine; Then enter the reverse osmosis membrane to separate most of the ions and organic matter; The primary pure water is then deeply removed by continuous electrodeionization or ion exchange resin; UV photooxidation device is used to reduce total organic carbon content; Finally, the ultrafiltration membrane removes the heat source, nuclease and other microbial residues, and the purity of the effluent is ensured by the terminal filter. The entire process is monitored by a microprocessor and maintenance operations such as flushing and regeneration are automatically performed.
Measurement methods and water quality indicators
The water quality of ultrapure water is mainly monitored in real time by online resistivity meter and total organic carbon analyzer. The resistivity reflects the ion content in the water, and the theoretical resistivity of pure water is 18.2 trillion ohms·cm at 25 degrees Celsius, which can be passed by the formula ρ = 1/σ calculation, of whichσIt is the conductivity. Total organic carbon is usually determined by ultraviolet oxidation-conductivity detection. In addition, microbial content is assessed by regular flat dish culture and particulate matter is detected with a laser particle counter. These indicators must meet the first-class water quality requirements specified in international standards such as ASTM D1193 or ISO 3696.
Influencing factors
The quality of effluent is affected by the composition of raw water, the performance of the purification module, the maintenance status of the system and the use environment. High hardness or high organic matter content in raw water will accelerate the failure of reverse osmosis membranes and resins; Insufficient sealing of the water storage system may lead to carbon dioxide dissolution and reduce resistivity. Pipeline material precipitates or microbial films can introduce pollution; Volatile organic compounds in ambient air may also enter water bodies through gas-liquid exchange. Regular disinfection, timely replacement of consumables, and reasonable system design are key to maintaining stable water quality.
Applications
In analytical chemistry laboratories, ultrapure water is used to prepare mobile phases for liquid chromatography and mass spectrometry; In the field of life sciences, it provides a pollution-free medium for cell culture and nucleic acid sequencing; The semiconductor industry uses it to clean the surface of wafers; Used in environmental monitoring for trace element analysis. Different applications focus on water quality parameters, such as molecular biology focusing on nuclease content, while trace analysis focuses more on metal ion background values.
Selection considerations
When selecting equipment, the peak daily water consumption and continuous demand should be clarified first, and the water production capacity of the system should be determined. Confirm the required water quality level according to the sensitivity requirements of the experiment, such as whether to pay attention to heat sources or dissolved oxygen indicators. The modular design allows for later upgrades, while the water-saving configuration reduces operating costs. Ease of maintenance, consumables replacement intervals, and water quality data traceability are also important considerations. It is recommended to refer to international standards for water quality grading, combined with the water quality clauses in specific experimental agreements.