Experience has shown that once more than three simultaneous chemistries are attempted the time involved in verifying and maintaining reagents, flow rates, pump tubes, etc. outweighs the time gained by analyzing all the analytes at once. Since the FS3100 was specifically designed with rapid changeover in mind it is actually faster to run one or two chemistries. While these chemistries are running, reagents and samples for the next tests can be prepared. The multitasking software allows sample tables for the next runs to be created while data is being collected further speeding the process. Also, keep in mind that all that is required to change from one method to the next is changing a cartridge and an interference filter.

IC can analyze Ammonia, Cyanide, Total P, TKN, and Hardness. The problem with IC and these parameters is that they are single analytes that cannot be determined simultaneously.

Analysis “lag” time is a function of the chemistry / method and NOT whether it is FIA or SFA. Color develops at equal speeds regardless of whether there are air segmentations or not. Since dispersion forces FIA methods to elute peaks within 1 – 2 minutes there is an appearance that FIA is faster. Only methodologies that cannot be performed by FIA, or that perform better by SFA require a 5 – 15 minute lag time for a reaction to occur.

Yes, when using the auto dilutor calibrations can be prepared from a single stock.

The “shutdown” time is a function of the internal volume of the flow path and has nothing to do with air segmentation; the “shutdown” time is chemistry cartridge dependent and is identical for FIA and SFA.

Carryover is an integral part of all continuous flow methods and is a result of longitudinal dispersion that occurs as liquids travel down tubes. Segmentation minimizes the dispersion resulting in the near rectangular output of a SFA signal. FIA methods, on the other hand, rely on the carrier solution to wash remnants of the sample out of the tubing. The Gaussian shape of FIA peaks is indicative of the dispersion within the tube. In fact, it is carryover that limits the applicability of FIA methods to reactions that develop color quickly so that the internal volume (flow path) is kept small. Larger flow paths result in FIA peaks with carryover so extreme that sample segments blend with each other. It is in these cases that segmentation is required.

All continuous flow methods (SFA and FIA) have highly precise sample volumes and analysis times. While FIA injects with a valve, SFA injects by time. Each standard and sample is exposed to exactly the same conditions meaning that reactions in both FIA and SFA methods do not need to be carried to completion (steady state). In addition, it is the internal volume of the tubing (travel time) and the injection volume (peak width) that determine the analysis time per sample. SFA peaks do not broaden as they travel through the tubing. This means that in methods with large travel time SFA methods have faster analysis times, while in methods with small travel times the analysis time is essentially equal.

The amount of time necessary to “condition” a manifold is a function of the internal volume of the manifold tubing and not whether bubbles are present. It is important in all continuous flow methods to rinse the manifold with reagent water (or reagent water with surfactant) prior to analysis until a steady baseline is obtained.

A fundamental advantage of FIA is the simplicity of the cartridges, apparatus, and methods when segmentation is not used. However, the lack of segmentation limits the ruggedness of FIA methods and requires careful adherence to flow rates, and total sample flow path volumes to avoid significant changes in throughput, dynamic range, and detection limits. SFA, on the other hand, is more forgiving in that even significant increases in total sample flow path do not adversely affect throughput, dynamic range, or detection limits. Each technique has its own advantages and deficiencies and the choice of technique for a given analysis needs to be made based on the chemistry being automated, and not solely on preference for FIA or SFA.

Flow analysis has advantages over manual methods that include smaller sample volume and reagent consumption, greater reproducibility, and higher throughput. Typical continuous flow methods can analyze samples from 30 up to over 300 samples per hour. Normally, throughput is limited to 30 – 90 samples per hour to allow baseline resolution between samples, better detection limits, and a larger calibrated range. Since continuous flow methods (SFA and FIA) analyze every sample and standard at exactly the same time following injection into the continuously flowing stream reactions do not need to be brought to equilibrium (steady state).

Both Segmented Flow Analysis (SFA) and Flow Injection Analysis (FIA) are continuous flow methods that rapidly process large numbers of samples. SFA and FIA utilize the same basic operation including a peristaltic pump that continuously merges samples and reagents in exact proportions that are determined by the internal diameter of plastic pump tubing. All continuous flow methods allow automated dilution, filtration, digestion, dialysis, derivitization, and/or incubation. The primary difference between SFA and FIA is that SFA mixes by turbulence produced by the introduction of a segmentation gas (bubbles) and FIA relies on dispersion and generation of an asymmetric Gaussian shaped color gradient with a detector response being proportional to concentration.