The common principle of a fully automatic flow injection analyzer is based on flow injection analysis (FIA) technology. By injecting the sample into a continuously flowing carrier current, the mixing, reaction, and detection of the sample and reagent are automated. Its core principles include sample injection, controlled dispersion, timing control, and optical/electrochemical detection. Combined with modular design and software control, it can quickly and accurately complete multi parameter analysis. The following is an introduction from five aspects: principle foundation, instrument structure, workflow, detection methods, and technical advantages:
Fundamentals of Principles
Flow Injection Analysis (FIA) was proposed by Danish scholars Ruzicka and Hansen in 1975. Its core is to achieve quantitative analysis by controlling the dispersion and mixing process of samples and reagents in the liquid flow under non-equilibrium conditions. This technology injects the sample into a continuously flowing carrier current (such as reagent solution or water) in the form of a "sample plug". During the flow process, the sample mixes and reacts with the reagents in the carrier current to form a detectable substance. Finally, the signal changes (such as absorbance, electrode potential, etc.) are measured by a detector, and the sample concentration is calculated using the standard curve method.
Instrument structure
A fully automatic flow injection analyzer typically consists of the following modules:
Infusion system: using peristaltic pumps or injection pumps to drive the flow of carrier fluid and reagents. The peristaltic pump generates negative pressure suction by squeezing the elastic pump tube with a roller, and the flow rate is determined by the pump head speed, pump tube inner diameter, and compression degree; The infusion pump is driven by a stepper motor to achieve more stable flow rate control, which is suitable for high-precision demand scenarios.
Sample injection system: Use a rotary injection valve (such as a six way valve) to accurately inject a certain volume of sample into the carrier current. The injection valve switches the connection state between the sampling ring and the carrier/reagent flow path by rotating, completing the quantitative collection and injection of samples.
Reaction system: The sample and reagent are mixed and reacted in a reaction coil (usually a polytetrafluoroethylene tube). The coil design optimizes the mixing effect by increasing radial diffusion and reducing axial diffusion, while avoiding excessive sample dispersion and ensuring reaction reproducibility.
Detection system: equipped with optical detectors (such as spectrophotometers) or electrochemical detectors (such as ion selective electrodes). Optical detectors measure changes in sample absorbance through flow cells, while electrochemical detectors achieve quantitative analysis through changes in electrode potential.
Control system: Automated control of instruments is achieved through computers and specialized software, including functions such as flow path switching, parameter setting, data acquisition and processing.
workflow
Current carrying propulsion: A peristaltic pump or injection pump pumps a current (such as water or reagent solution) into the system at a constant flow rate.
Sample injection: The injection valve injects a quantitative sample into the carrier current in the form of a "sample plug" to form a sample strip.
Mixed reaction: The sample is carried in a reaction coil and mixed with reagents in the carrier current, resulting in a color reaction or other chemical reaction.
Signal detection: After the reaction, the solution flows into the flow cell, and the detector measures signal changes such as absorbance and electrode potential.
Data processing: The computer calculates the sample concentration using the standard curve method and outputs an analysis report.
detection method
Optical inspection:
Absorption spectrophotometry: Quantitative analysis is achieved by measuring the degree of absorption (absorbance) of a sample towards specific wavelengths of light, and is widely used for parameter detection such as total phosphorus, total nitrogen, and ammonia nitrogen.
Fluorescence method: using the fluorescence intensity emitted by the sample after excitation for detection, suitable for trace substance analysis.
Chemiluminescence method: Detection is achieved by measuring the intensity of the light signal generated by chemical reactions, which has high sensitivity characteristics.
Electrochemical detection:
Ion selective electrode method: using the selective response of electrodes to specific ions to measure potential changes, suitable for parameter detection such as fluoride.
Voltammetry: Detection is achieved by controlling electrode potential and measuring current changes, commonly used for heavy metal ion analysis.
technical advantage
Fast analysis speed: 60-120 samples can be analyzed per hour, and in special scenarios (such as wastewater S ² ⁻ detection), it can reach 720 samples per hour.
High precision: The relative standard deviation (RSD) is usually less than 1%, and the reproducibility is excellent.
Low reagent consumption: Only tens to hundreds of microliters of reagent are required for each analysis, significantly reducing detection costs.
High degree of automation: Modular design supports multi-channel independent operation, which can synchronously detect multiple parameters such as total phosphorus, total nitrogen, ammonia nitrogen, volatile phenols, etc., in accordance with national standard methods.
Widely applicable: Suitable for water quality monitoring, soil analysis, food testing, environmental emergency monitoring and other fields. Portable models (such as iFIA5+) can be equipped on emergency monitoring vehicles to meet the needs of rapid on-site detection.