Flow Injection Or Segmented Flow Analysis - What Are the Similarities and Differences?

The reason to use SFA or FIAapprovals. Since the EPA considers FIA equivalent to
The reason to automate is so that you can run moreSFA, OI did not obtain EPA ATP letters. There are
samples. Running more samples is the same asalso several FIA methods that are EPA approved
increasing your productivity. Having an instrument runwithout an SFA equivalent, for instance CN by
samples for you decreases your labor costs. HavingOIA1677.
the instrument do all those boring mixings andIn Flow Injection analysis the sample is injected by a
shakings increases your day to day precision. Thisvalve into a carrier stream. The sample solution does
improves quality and really helps with that QA/QCnot pass through peristaltic pump tubing prior to the
program. Whether you are a research facility, avalve. Mixing occurs as the sample travels through
municipal laboratory, or a commercial lab, you cantightly wound Teflon mixing coils. Unlike segmented
benefit from automation.flow that may contain multiple samples within the
Almost any method that can be done manually cantubing all at the same time, Flow injection injects a
be automated. Time consuming steps such as manualsample and detects it before the next sample is
titrations can be replaced using instrumentation.injected.
Instruments can do digestions, distillations, dilutions,Comparison of SFA and FIA
and filtrations all for you. More importantly, is thatFlow Injection is basically a derivative of SFA without
these methods are always duplicated exactlyair segmentation. Both SFA and FIA mix sample and
ensuring that quality control procedures are met.reagents in a continuously flowing stream of
Your most expensive cost is labor, and after that isreagents. The reaction that occurs, the peak shape,
supplies. A flow analyzer will allow you to do morethe sensitivity, and so forth is all determined by how
samples in less time and increase the amount of timethe tubing is configured, where the reagents are
you or your staff spends on more important thingsteed in, and the length of the tubing that the
like running other samples, reporting results, and doingreactions are happening in. Instrument manufacturers
that dreaded paper work. Automated equipmentconfigure tubing "cartridges" according to published
uses less reagents and generates less waste thanmethodology, or develop methods based on
manual methods do. This is not about getting rid ofR&D and published works.
staff. This is about freeing up time so that staff canAn analyst can readily change and/or modify method
have time to prepare and run more samples. Theperformance simply by modifying any aspects of the
beauty of the auto analyzer is that it is runninganalytical cartridge. Since the segmentation of SFA
samples while you are doing something else.limits dispersion, SFA is a bit more forgiving than FIA
History of Flow Analysisin the length of tubing. For instance, the addition of
The original automated analyzer is the Auto Analyzerextra tubing on a FIA method can significantly change
invented by Leonard Skeggs in 1954. It took thepeak shape and sensitivity, while additional tubing on
Technicon Corporation three years to perfect it anda SFA system does not really matter. For example,
develop a commercial product. The concept ofat one of my previous laboratories we routed an
auto-analysis eventually branched out and has rootsSFA method that had a non-working heater cartridge
in almost every automated device we see today.through several feet of tubing to the fecal coliform
Flow Injection Analysis was a way to get out ofbath and then back to the detector. Adding several
buying a Technicon Auto-Analyzer because a personfeet of tubing would have been detrimental to FIA,
with a peristaltic pump, some Teflon tubing, and abut was un noticeable in the SFA method.
flow through spectrometer cell could fabricate theirLiterature is deceiving in sample size as SFA methods
own device. In fact, the first FIA instruments weretend to use less sample than FIA. Throughput by FIA
held together with Lego blocks. The first commercialis not faster, and in fact it has been demonstrated
FIA instrument was introduced by Tecator, thethat a well operated SFA system far exceeds FIA in
analytical branch of Perstorp.samples per hour. SFA mixes by an end over end
All continuous flow analyzers share a commonality ofsimilar to putting sample and reagent in a vial and
parts with similar functions. All have an autosampler,inverting. FIA mixes by what Ruzika termed
pumps, reagent mixing manifolds comprised of tubing,"controlled dispersion" which is harder to explain than
a flow through detector, and a way to collect theend over end, and is a result of solution flowing
signal. The signal is always expressed as a peak withfaster through the center than at its sides, and then
a maximum and a baseline, and the peak is either bellrapidly colliding with the walls of the mixing coils and
shaped, or rectangular.other flow interruptions placed in its path. SFA signals
Segmented Flow Analysis (SFA)do not have to be brought to a maximum, but
Segmented Flow analysis is the first auto chemistrytheoretical SFA should always be and the resulting
and is what Skeggs initially demonstrated to thepeak would be rectangular. Because of the "tunneling"
Technicon corporation. Segmented flow enjoys overthat occurs in FIA flow, a FIA peak is Gaussian.
50 years of success as a proven technology.It is hard to say exactly what the maximum time for
Segmented flow is the basis of multiple automateda SFA incubation is because the only limiting factor is
EPA and many other regulatory methods.the minimal carryover that occurs as solution
A typical segmented flow analyzer pumps the sample"transfers" from one segment to the next while
into the cartridge using peristaltic pump tubing. Thetraveling down the tube. Most FIA literature places 2
sample merges with an air segmented carrier stream,minutes at the maximum for FIA. In fact, Ruzika and
reagents are added and mixing occurs by end overHansen gave a 1 minute maximum for FIA reaction.
end mixing in coils as the sample is transported downAdvantages of Flow Methods
the path of the tubing. Depending on the internalMany methods are written specifically for continuous
tubing volume and the amount of time the transportflow analysis. Some examples are ammonia by EPA
from injection to detection takes there could be350.1 or Block digestion TKN by EPA 351.2. An
multiple samples inside the tubing at a given time. Forexample of a FIA method written specifically for FIA
instance, if the delay time is 10 minutes and samplesis OIA 1677. These EPA methods specify automated
are injected every minute there will be 10 sampleschemistry in the methodology itself. Other methods,
traveling within the tubing.such as the manual fluoride by ISE method, can be
Flow Injection Analysis (FIA)modified according to 40 CFR Part 136.6 and made
Flow Injection Analysis is considered as an acceptableinto automatic methods. Continuous flow methods
alternative to equivalent segmented flow methods. Inreduce manual labor and that reduction of manual
other words, though USEPA method 350.1 is alabor tends to make precision better and reduce
segmented flow method, the USEPA considers a FIApotential contamination. Flow methods also tend to
method equivalent. There are thousands of literaturehave lower MDL's than manual methods and a better
references to FIA methods, and multiple ATPchance of fewer QC failures.