Water analysis is essential to ensure its quality or to detect pollutants that should be removed by water treatment. However, water quality does not mean making the water suitable for human consumption; it depends on its end use. For example, completely different quality standards are applied in case of industrial water compared to those applied to drinking water, i.e., drinking water must be fit for human consumption, while industrial water should be free from any contaminants that may corrode or damage equipment.
Traditional analysis includes chemical analysis, colorimetry, spectrometry, chromatography, and atomic absorption. Although these techniques differ in sensitivity and accuracy, most of them are highly accurate. Nevertheless, they require sampling, expensive devices, and manpower; besides, they are time consuming and difficult to conduct onsite.
Microfluidics and lab-on-a-chip systems are advanced technologies that may replace the traditional methods of water analysis in the near future. Lab-on-a-chip technology employs microfluidics, which deals with very minute amounts of fluids in micro channels, to perform analysis. The lab-on-a-chip device is a chip that resembles electronic chips, but with micro-channels instead of electrical circuits. It shrinks the lab to the chip size, and can perform complete analysis or even series of analysis.
Using the lab-on-a-chip technology in water analysis can reduce time and manpower in the sampling process, because this technology can offer immediate, onsite results. In addition, this technique is much less expensive and offers higher accuracy, because of the small volumes analyzed and the possibility of eliminating the sampling process, which reduces the human error.
Many detection techniques are being employed in lab-on-a-chip systems, such as chromatography, electrochemical analysis, mass spectrometry, fluorescence, and laser.Components of Lab-On-A-Chip Systems
The main components of a lab-on-a-chip system for water analysis are: liquid delivery system (injector and fluidic transporter), mixer, reactor, separator, and power supply.
The Injector is used to deliver precise volumes into the chip. The most common types of the injectors are syringe pumps and robotic pipets.
Transporters control all aspects of the flow. They can be active, which need an energy source, or passive, which are achieved by manipulating the geometries of the channels and do not require any energy source. The choice between the active and passive types is based on the application. There are multiple types of active transporters, but the most preferred is electrochemical pumping systems, such as micro syringe pumps, because they eliminate the design complexity.
Mixers are used to mix different fluids into the channels. Similar to the transporters, the types of mixers are divided into passive, which are achieved by design manipulation, and active, which require power.
The Reactor is where the reaction takes place. There are three types of reactors used in lab-on-a-chip systems: gas phase, liquid phase, and packed-bed reactors.
Controllers are used for controlling all types of activities in the chip as well as data acquisition and signal processing.
Power supplies, such as batteries, are essential to run the lab-on-a-chip systems. Many research studies focus on finding more advanced power supplies, because some types of lab-on-a-chip systems require high voltage.Current Applications in Water Analysis
Lab-on-a-chip technology is rapidly developing and being used in different industrial and research fields. Most biological lab-on-a-chip devices are commercialized, while those for water analysis are still developing. However, some lab-on-a-chip applications in water analysis are already established, such as pH testing and detection of various chemicals (e.g., nitrates and nitrites, manganese, phosphates, and silicates). For example, the microfluidic pH analysis uses sulfonephthalein as the main indicator. It includes the absorption cell, a static mixer, as well as a syringe pump and four valves attached to the chip to regulate the flow.