Flow injection analysis (FIA) is an approach to

chemical analysis Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or quantification may constitute the entire analysis or be combined with another method. Separati ...

. It is accomplished by injecting a plug of sample into a flowing carrier stream. The principle is similar to that of Segmented Flow Analysis (SFA) but no air is injected into the sample or reagent streams..

Overview

FIA is an automated method of chemical analysis in which a sample is injected into a flowing carrier solution that mixes with reagents before reaching a detector. Over past 30 years, FIA techniques developed into a wide array of applications using

spectrophotometry Spectrophotometry is a branch of electromagnetic spectroscopy concerned with the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses photometers, known as spec ...

, fluorescence spectroscopy,

atomic absorption spectroscopy Atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) is a spectroanalytical procedure for the quantitative determination of chemical elemlight) by free atoms in the gaseous state. Atomic absorption spectroscopy is based o ...

mass spectrometry Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is use ...

, and other methods of instrumental analysis for detection. Automated sample processing, high repeatability, adaptability to micro-miniaturization, containment of chemicals, waste reduction, and reagent economy in a system that operates at microliter levels are all valuable assets that contribute to the application of flow injection to real-world assays. The main assets of flow injection are the well defined concentration gradient that forms when an analyte is injected into the reagent stream (which offers an infinite number of well-reproduced analyte/reagent ratios) and the exact timing of fluidic manipulations (which provide exquisite control over the reaction conditions). Based on computer control, FIA evolved into Sequential Injection and Bead Injection which are novel techniques based on flow programming. FIA literature comprises over 22,000 scientific papers and 22 monographs.

History

Flow injection analysis (FIA) was first described by Ruzicka and Hansen in Denmark and Stewart and coworkers in United States in the middle of 1970. FIA is a popular, simple, rapid, and versatile technique which is a well-established position in modern analytical chemistry, and widespread application in quantitative chemical analysis.

Principles of operation

A sample ( analyte) is injected into a flowing carrier solution stream that is forced by a

peristaltic pump A peristaltic pump, also commonly known as a roller pump, is a type of positive displacement pump used for pumping a variety of fluids. The fluid is contained in a flexible tube fitted inside a circular pump casing. Most peristaltic pumps work t ...

. The injection of the sample is done under controlled dispersion in known volumes. The carrier solution and sample then meet at mixing points with reagents and react. The reaction time is controlled by a pump and reaction coil. The reaction product then flows through a detector. Most often, the detector is a spectrophotometer as the reactions usually produce a colored product. One can then determine the amount of an unknown material in the sample as it is proportional to the

absorption spectrum Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating f ...

given by the spectrophotometer. After moving through the detector, the sample then flows to waste. Detail of sample dispersion When a sample is injected into the carrier stream it has the rectangular flow. As the sample is carried through the mixing and reaction zone, the width of the flow profile increases as the sample disperses into the carrier stream. Dispersion results from two processes:

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

due to the flow of the carrier stream and

diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

due to a concentration gradient between the sample and the carrier stream. Convection of the sample occurs by

laminar flow In fluid dynamics, laminar flow is characterized by fluid particles following smooth paths in layers, with each layer moving smoothly past the adjacent layers with little or no mixing. At low velocities, the fluid tends to flow without lateral mi ...

, in which the linear velocity of the sample at the tube's walls is zero, while the sample at the center of the tube moves with a linear velocity twice that of the carrier stream. The result is the parabolic flow profile, before the sample passes through a detector to a waste container.

Detectors

A flow-through detector is located downstream from the sample injector and records a chemical physical parameter. Many types of detector can be used such as: * spectrophotometer * fluorimeter *

ion-selective electrode An ion-selective electrode (ISE), also known as a specific ion electrode (SIE), is a transducer (or sensor) that converts the activity of a specific ion dissolved in a solution into an electrical potential. The voltage is theoretically dependent ...

* biosensors * mass spectrometer

Marine applications

Flow injection techniques have proven very useful in marine science for both organic and inorganic analytes in marine animal samples/seafood. Flow Injection methods applied to the determination of

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

(

histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the de ...

, L-lysine and

tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the Gr ...

), DNA/RNA,

formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...

, histamine, hypoxanthine, polycyclic aromatic hydrocarbons, diarrheic shellfish poisoning, paralytic shellfish poisoning, succinate/glutamate, trimethylamine/ total volatile basic nitrogen, total lipid hydroperoxides, total volatile acids, uric acid, vitamin B12, silver, aluminium, arsenic, boron, calcium, cadmium, cobalt, chromium, copper, iron, gallium, mercury, indium, lithium, manganese, molibdenum, nickel,

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

, antimony, selenium, tin, strontium, thallium, vanadium, zinc, nitrate/nitrite, phosphorus/phosphate and silicate.

References