Why FIAlab

What is Flow Injection Analysis?

Flow injection analysis (FIA) is a technique for automating wet chemistry by pumping small volumes of samples and reagents through a flow stream in an organized, systematic way. Reagents and sample mix in this stream creating a chemical reaction. These chemistries are usually colorimetric - meaning a color develops as a result of the sample and reagents mixing. These reactions are positively correlated: more color development signifies that more analyte is present. This change in color is then detected by any variety of spectrometry or absorbance measurements. The greater the color development, the greater the absorbance value. There are also FIA methods that utilize turbidimetric measurements. Instead of a color developing in the flow stream as one observes in colorimetric reactions, a precipitate is formed. This is called turbidity. The turbidity can also be measured using spectroscopy.

In order to calculate the concentration of unknown samples, a calibration curve must first be constructed using standards of known concentrations. By comparing the response or absorbance values of these standards to that of unknown samples, one can accurately calculate the concentration of unknown samples. A linear or quadratic formula is created from known standards and the responses of unknown samples are plotted against this to calculate the unknown concentrations. A typical calibration curve will encompass the full range of possible unknown values.  

There are four main components on a FIA analyzer. These are the peristaltic pump, the selector valve, the mixing manifold, and the detector.

The peristaltic pump is the driving force of an FIA instrument. This pump will drive reagent and samples through the entire system. These pumps have “lines”. Each line leads to a single reagent or sample. Most FIA methods utilize four lines: sample, carrier, reagent one and reagent two. Current technologies have allowed these pumps to be extremely efficient and smooth. Peristaltic pumps in the past have been wasteful and jumpy. FIAlab only chooses pumps that do not pulsate or use excess reagent. This significantly calms baseline noise and reduces waste production.

The injector valve is a critical component in an FIA system. As the autosampler probe travels from sample to sample, it enters and leaves liquid. All the while, the peristaltic pump continues to run. The pump draws air as the probe is out of solution, and air travels toward the FIA system. The selector valve is what allows air to bypass the system. It directs collected air to waste and then injects pure sample into the flow stream. As a result, you do not have to deal with problematic air bubbles and the throughput of the analysis is greatly increased. The use of a selector valve distinguishes FIA from segmented flow analysis (SFA) where air bubbles are left to flow through the system.

It is important in FIA methods that reagents and sample mix in a step-wise and systematic fashion. The mixing manifold acts as the crossroads for reagents and samples. For example, you must first react reagent one with sample and allow time for these solutions to mix before introducing sample to reagent two. Without doing so, you will not have a proper chemical reaction and no measurable colorimetric reaction will take place. FIAlab has created the smallest, most efficient mixing manifold on the market. We call it the Lab-On-Valve. This manifold is the reason why our analyzers are also the smallest on the market.

The last part of an FIA system is the detector unit. This is comprised of a light source, a flow cell, a spectrometer, and fiber optic cables to connect these components together. A spectrometer measures absorbance over time. But, it can only do that if it has a consistent flow of light - that is why a light source is included in all FIA systems. The flow cell sits between the light source and the spectrometer. A flow cell has four ports - each connected to one other. Two ports are allocated for the entry and exit of solution. The other two ports are directly across from each other creating what we call the “optical path”. These ports are water-tight and connect to the fibers. One fiber leads to the light source and the other leads to the spectrometer. This configuration allows for the light source to shoot light to the spectrometer as the colored sample passes through the optical path and eventually to waste. That is the exact moment when absorbance readings are taken by the spectrometer.

FIAlab is the only FIA manufacturer to utilize a spectrometer. Most instruments will use a photodiode. A spectrometer allows for the end user to utilize the full spectrum of light which makes a FIAlab analyzer more useful, versatile, and easy-to-use.