Tips for Selecting the appropriate Nutrient Analyser

Flow injection analysis first appeared in the 1970’s and has evolved into a larger group of automatic chemical analysers. The current technologies in this group are:

Flow Injection Analysis (FIA)

Segmented Flow Analysis (FIA)

Discrete Analysers


Different Technologies.

Flow Injection Analysis (FIA) as a basic description involves specific analyte colour reagents being pumped through a detector able to detect different optical densities.  Into this flow a small accurate volume of sample is injected into the flow and mixes with the reagents and moves through the reaction coil and detector.

Segmented Flow Analysis (SFA) evolved from Flow Injection Analysis by creating sample partions in the stream by injecting bubbles between the samples. The partitioning bubbles meant less diffusion of the sample and a more concentrated ‘peak’ with less sample being injected.

Discrete Analysers are the more recent technology with the sample being ‘partioned’ into its own cuvette with reactants as a discrete or individual reaction.

Discrete Analysers can be either direct or indirect read instruments.

The direct reading discrete analyzer transfers via the robotic arm the sample and reagents direct to the cuvette where the optical density will be read.

The indirect reading Discrete Analyser initially transfers the sample and reagents to an intermediate reaction cuvette where the colour development progress’. Once the sample colour has saturated in the reaction cuvette, it is pumped through a common  flow-through cell for all samples where the optical density is measured.


Advantages and Disadvantages

Flow Injection Analysis (FIA)

  1. Able to attain very low detection limits by using long path-length cells, up to 50mm, giving up to 5x improvement in measurement levels.
  2. Use of dialysis system allows separation of difficult matrix as in soil samples.
  3. Fluidics need to be run for some time to stabilize before starting system.
  4. Each analyte to be analysed will require a separate fluidic path module to be added to the system.
  5. Ideal for large numbers of samples, greater than 150 per day, but can be expensive for large numbers of analytes on each sample.
  6. RSD’s dependent on condition of pump pulsations.


Discrete Analyser (DA)

  1. Very flexible with extra methods being able to be added or subtracted from a run.
  2. Fast start up, no fluidics to prime, minimal operator time.
  3. Flexible use of multiple reagents, calibrants and extractants.
  4. Detection levels not as good as FIA as swap out path-length cell not available
  5. Easy diagnostic testing.
  6. Low cost per sample to operate.