Segmented Flow Analysis (SFA) is an automated continuous-flow wet chemistry technique in which regular air bubbles are introduced into the liquid stream to divide it into discrete segments. Each air bubble acts as a barrier between adjacent sample and reagent slugs, preventing cross-contamination between consecutive samples (carryover) and promoting mixing within each segment as the liquid churns around the bubble.
SFA was invented by Leonard Skeggs and first commercialised by Technicon in the late 1950s through the AutoAnalyzer platform. It remains one of the most thoroughly validated automated chemistry methods in existence, with validated methods for hundreds of analytes in water, wastewater, soil extracts, plant tissue digests, and industrial process streams.
In practice, a peristaltic pump draws sample from a sampler tray, mixes it with one or more reagent streams, and pushes the combined flow through coiled glass or PTFE tubing where the chemistry reaction develops. An air segmentor introduces bubbles at regular intervals. After the reaction is complete, a debubbler removes the air before the stream passes through a detector, typically a photometric flow cell.
SFA is suited to routine, high-volume batch work where the same analyte must be measured in many samples per run. Throughputs of 20 to 90 analyses per hour per channel are typical depending on the method. Multi-channel configurations allow the same sample stream to be split and analysed for multiple parameters simultaneously.
The FS3700 Chemistry Analyser from OI Analytical supports SFA alongside Flow Injection Analysis (FIA) and variants including iSFA (improved segmentation for low-carry over at high sample rates) and SFIA (segmented flow with multiple channels).
Key Points
- Air bubbles segment the stream to prevent carryover between samples
- Supports 20 to 90 analyses per hour per channel depending on method
- Validated for cyanide, nutrients (ammonia, nitrate, phosphorus), and many other parameters
- Multi-channel setups allow simultaneous multi-parameter analysis from one sample stream
- Decades of validated methods in ISO, ASTM, and EPA frameworks
Relevant Standards
- ASTM D6888 / OIA-1677 (available/WAD cyanide, ligand exchange, gas diffusion, amperometric detection)
- ISO 11732 (ammonia/ammonium)
- ISO 15923 (general principle)
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Frequently Asked Questions
What is the difference between SFA and FIA?
Segmented Flow Analysis uses regular air bubbles to divide the stream into discrete slugs, which reduces carryover and improves mixing. Flow Injection Analysis uses no air — instead, a precise plug of sample is injected into a flowing reagent stream and the system relies on controlled dispersion and tight timing. SFA generally provides better precision for batch work; FIA is often faster for single-analyte monitoring.
Is SFA suitable for cyanide analysis at mining sites?
Yes. Methods such as OIA-1677 and ASTM D6888 (available/WAD cyanide by ligand exchange) are routinely run on SFA platforms. The FS3700 supports these at throughputs up to 60 samples per hour, making it practical for the sample volumes typical at mine site laboratories.